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RECORDED SIMULTANEOUSLY AT SEVEN M NTAIN. I. STATIONS .... Py means of a station network built wp in the Uetterstain Mountains ı.orthern Alps) ...

58- 645 C) AFCRC-TNReport Technical DES BEHAVIOUR OF ATMOSPHERIC ELECTRIC MAG NTAIN RECORDED SIMULTANEOUSLY AT SEVEN M STATIONS BETWEEN 700 AND 3000 METR S ABOVE SEALEVEL

I

4RESULTS OF ANALYSIS OF THE FINE AND THE DISTURBED i

WEATHER DATA, WITH SPECIAL ATTENT:ON BEING GIVEN TO PRECIPITATION AND ITS NITRATE AND NITRITE ION CONTENTS

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TSL-121-2/65

DATE PROCESSED' PROCESSOR:

'

y

TZC HNICAL

RIPORT

DMATIOUR OF A•!KSP]rC EILECTRIC MANrITUD• RECORDED SDIMUIMA2I•StLY AT SIU• MOUiMAIU STATIOCS BETWEED RUUIWS OF ANALYSIS OF TH

700 AND 3000 mum

ABOVE SALKIL.

FINE AND THE DISTURBED WEiTHER DATA,

SPECIAL ATENTIOIN BEING GIVE

TO PRECIPITATICN AND ITS NITRATE

ITRT

I0

Reinhold

WITH AND

CONTETS

R o i te r

July 1958

Cotr. t No. A? 61 (514)

- 949

The "[email protected] reported in this document has boon sponsored in pe•rt

by the

Geophysics Reeearch Directorato of the Air Force Cambridge Research Center, AIR RZSEANCR AND DEMLWf COWAND, under Contract No.

Al 61 (514) - 949

Contractors Adr"es Dr. Reinhold

UNITED STATES

AIR FORCE,

through the Buropean Office,

R e 1 t o r

farchant, Oberbayern,

ARDC* Germany

Table of Contents Page No. Acknowled~Anments 1. Introduction

I 2

2.* Recordine Instruments 3. The Station Network 4. The behaviour of atmospheric electric mimwitudes, observed simiultaneousl-y at'different alt itudes. during yrecipitationE 4.1. Behaviour of atmom~vheric electric am.Awitudee on typicl dews surve~ed with help of synolptio qhaxtds 4.1.1. Shower precipitation

4 5

4.1.2. Non-ehowery precipit-tion 4.1.2-.1 Light precipitation out of Altoetratum or Nimboetratus 401.2.2. Reavy' or sontinuous precipitation out of Nimbostratus 4.1.2.3. Periodical variations of the foreign field during precipitations *ose 41.2.1. SpeWcia 4.2, Results of the statistical

-

syuoytic ,--,-aions

4.2.1. Survey on total iiusiberu 4.2.2. Snow showers and rain showes, 4.2.3. lfon-showery precipitation; importance of the mielting process 4.2.4. Strength and sign of the potential gradient at different aIlt tudes during rain or snow 4.2.5. Strength and sign of the potential gradient below Altostratus with or without precipitation falling out of this 4.2.6. Influence of type and also of the snow cry'stals on the strength of the foreign field during snow-fall1 4.2.7. Relation between lability legree of the stratification and frequency of the si,:i reversals of the foreign field during precipitation

8 8 24 24 24

34 34 55 55 55 5S 60

62

64 65

S. The behaviour of the foreimm field durin.a driftins snow

72

6. Suni of the potential gradient below and nearZ thunderclouds

75

S~vand conclusions for sections 4A. S, and 6

80

Page N~o. 64

7*. Obsorvatlms~ made duariM Poehm 7.1. The behaviour of atmospheric electric Malitudes at diffe et altItudge Gurinz foehi 1.?. Varitions of the natu~ral neiAlqtivit-y ig the akr duar-IA southErn winds over the Alne

84 90

8. Dqhaviwq of atomoenhrlo *lectrip namitDAdem at station ZBaOvitse. obsorve4 Swh this*Station ent*Er int2 or comes out or f&Z 0.1. XpjliJ.w- ex *6eOf the wbsa2§M eocuMLrd. when ta tion Zuts~nte'at the toi- of clowt sheete in an inversion IsZer 6.2. Indiviftal examI2e 4f the uhenomena ococtrnlA when pJtation Zulevitse Ls at the bass 2f Altota~t 8.3. Statistloal ewialution of the data obttAine when station Ziagent29 Is at the too of cloud sheet. In an inversion la~r

105

end SIX eeorh a~rxent at 9. bea~viou Of 90tentAl "1ient different Saltvtudes in the mmeeno of b"nrervigns. eeoecirally of euah with sheet olqoud. within the area, of the station potwork

107

92 92 9

10.. QaeCtric codciiy LbM 11

fte4 between 700 and IM0 a nealevejjjJnluevAso of convetlon gd sothernwinds

nla*o h-ntrl;~cciiyo the air on the atr Peric electric pAq~itiades at different levels

12. Thunderstorm forecasts with muherloerecordiana Concusions of sat io 11

III

Crrrlat

aon *et-e

th*b

etr

Inrdcineodocemcl r140.

-14.3.-Results

121 124

131 sAr

rquny

14. Relations between the contents ofnirt

lie

dptie

lsi

135 139

III

Page No.

14.3.

139

Results 14.3.1.

of a diffe"enoe in

Influesno

altitude

Y03'

of about 1100 a (3600 feet) on and N02' 14.-3.2.

139

in precipitation

Cotparison of

02 # and N10

in

precipi-

tatlan with omtents in dew or riwq both oollected in the valley 14.-3-3.

precipitattone and artlfiqlal both collected in the valley 14.3.4.

140

Influence of point discharge near the ground on the NO ' and So 2I contents in dew or rise

141

Influence of the lability energy in the 700 - 5W0 ub lyer on the 90O '1a d NO2 contents of precipitation

collected In

the valley

143

14.3.5. Influenoe of the frequency of sign reversale of the foreign tield on the N01 ad so2' in 14.3.6. 14.4,

collected 145

Tabular survey of results

View points on the oriKin of nitrate In Preolotptious

14#5.

15,

contente of prec-pitations

the valley

146 and nitrite

14.4.1.

Sources of atm6spberio nitrogen oxide and nitrogen dioxide (N02)

14.4.2.

Reactiona of nitroten oxidea and nitrogen dioxides with water

Disous•ion

(NO)

and conclusione

151 152 153

Mean diurnal variations of the atmoepheric electric qM

itudes per month or seasop at each station during

156

fine weather 16.

151

Comparison of the fine weather behaviour of the atmospheric electric meamnitud.e with water va.prur resMsurs. & Lw-value,

tempersture R ferenoe s

and potential equivalent

158 160

Iv

Py means of a station network built wp in the Uetterstain Mountains continuous recordings

ý.orthern Alps),

cr.rriod out during all

of atmospheric electric elo=ents were The seven stations are

seasons and weather conditions.

situated at different altitudes between 700 and 3000 a a&bae sealovel,

their

horizontal distances being relatively small.

The potential rradient was recorded at each of the stations, current of four of them.

the air earth and the

point discharge carrent, 9pherics,

Besides,

rumber of positive and negative small ions were recordpA at moe of the stations. The positive and negative conductivity of the air was measured through several to time in

hours at each station from ties trate Ion contents

and ni-

The nitrite

o weathqer.

f

as well as the p% value o? each precipitation were determin-

ed; the samples wore colleoted separately for each precipitation or, in oa*@e

of longer precipitation,

stations,

if

for several hours,

and that at on' of the valley

possible simultaneously also at a neighborinug peak station.

Meteorologioal

obsev.,ations wore nade at all

two of

the sta.ires.Portunately

the stations are housed at observatories st the German Weather Bervios, e us with their observation rerilts

are supptl

the

station Parohant,

where are our "hoadquarters"

almost the whole station network,

sad,

if

needed,

which

recordas

at

and which comands a view of

the meteorological obsiervations

include ope-

o1*1 observations on cloud development and precipitatlon, types. The obtained data and observations were evaluated extensively.

The avers-

go diurnal variations of the atmospheric electric elecmwts per month or season at the different stations in

fine weather were used as s bass for the study of

bad weather phenomena. Since the stations are a sort of step-ladder through mor

than 2000 a of atmosphere,

the network is

especially

fit

for .raMLalug

cloud and preuipitation problem simultaneously at different altitudes. evalutation of the records,

In

the.

relations between meteorological and

themrforoe

acoompanying atmo spheric electric phenomena were lookolYand found out for instance with respect to space ohrge

at

shoeet

ae"

banmdsriea,

of sign revere&lo of the atmspberie eleetrie elements at during =stable

stratifloatlonia

sign and @L-z rever-als in precipitation

with the melting sons level being J,.t derstore

within the station network,

etc. Thun-

problems were approaabhd by ezamining snow crywjtal friction and break-

ing and their electrio&l effects snow,

frequency

Wifferent altitudes

at the different stations during drifting

and further by gathering experieaoe with respect tlo test thunderstorm

v

forecasts based on ephorice recording* and to the corrolaticn between thunder. storm occurrence and sun flares. The nitrate and nitrite contents of precipitation proved to be indicatory of atmospheric electric coalitions at such altitudee,

too,

where t-wre are no recording stations. Besides the eventual

function of thene contaainant3

in tne process of cloud electrification

in

considered. For all the aitoorelogical eand atmoaheric electricsituaticns dealt with

sing!* exanples are described and illustratea by recoraing exa-ples showing the records of the seven stations cne above th.ie other on one figure ("s yn-

optic cnArts"I.

?eyond this, the results of the nw ricý! and otatistical

analy3is of the [email protected];krlc electric recording c-urves are Fiven in a great numzber of graphic representaticns.

Acknowledgements The research reported in this document was &&de possible in part through support end sponsorship extended by the Geophysies Research Directorate of the Air Force Cambridge Research Center, ARDC, tSkP, un,±er Contract 1? 61 (514)-949 throug~h the European Office, ADEC. Valuable assistance is due tklso to the Geruar. Weather Service (Deutacher Wett~rdier.st) ruid tý' several Mo-.nt&ain Railway Com;pnies; we wish to express cur gratitude to the following organizations and their nuasroums assistants: Doutscher WatterdienAto Vettaramt Ehinchen (Direktort Dr. R. ARflflOLD) Inatrumenteneat Sild (Leader: Diplom-Lngeniirur L. WOLLIA) Bergwetterwarte Zugapitze (Ueadert Diplo~a-Meteorco1oge L.WMN1, .HERSS) Diploa-M~toorologe Vetteresttion Ga-mierh (Leaders Oberinspektor 1I.JURISCH) Dayariache Zugspitxbahn iktle.gesellechaft (Direktars Diplon-Ingenieur

R. scwIor) Tiroler Z~ugopitzbahn AktIengesellschr'ft (Direktor: Inge-niour W.PAINIK) Wankba.hn Aktlengoseilac'.at 'Techn.Ler-dcr: Diplosingenitur H.KIRSCHBAUER) Furthermore we wish to express our thanks to the following firmai Aligemoine Electrizithtegosellschaft A.G. (AMi) Perlin-Vest Calor-Emag A.G. Ratingeri bei DUsseldorf Hj~rtmann wid Braumn A.C. Frankfurt Sieumes und Halake A.G.,

/

main

linchen

ia are indebted in many respects also to the following scientific institute&& Max Planck Inatitut fUr Silikatfornobung, Berlin-Dahles (Dozent Dr. L.HOLZAPMZ) Institut fitr Technisoheo Ilektronik der Technischen Hochschule Elnohen (Professor Dr. xDOLL)

has made possible the nmewrical. evaluation of the fine weather records by granting a subsidy (Sachbei-

The Y)I)FSCHE 7ORSCHUNG 3ZflMC:{ir hilfe).-

-

The research was carried out in co-operation with Mrs . Mirian RL1T-ZR.

1. Introduction In Technical Report A? 61 (514)-732-C

we dealt with the first part of our

studies an atmospheric electricity supported by the Geophysics Research Direc torate of the US Air Force Ca:-bridge Research Center, ARDC. This Report covered r. period of two years, during which the station network was completed ard messurin~g instruents were proved; furthermore, we endeavoured to obtain a prelimin&-. ry ins ight into the mawifold forms of atmospheric electric phenomena, the mnultiplicity of which appears clearly, if the connections with meteorological pro-. cesses are cot.--idered. It was nece3sary, within theoa, first two years, to obtnaln Treer and survey, to classify all the diverse single Fphenozena, and to arrange them according to types. This classifying and finding out of types was carried out by means of asynoptic charts", which contain all the recorcls and observations of one day from all the stations. A more or less large number of single [email protected] were given to describe and establish the single types. 11owver, already in the period covered by our first Technical Report, mumerical evaluations of the single cases were started, which were intended to be followed by a statistical t~reatment of the data. The scope, as to the methods, of the second investigation period, covering the two years 28 June 1956 till 27 June I95

and described in this report, was

a) to continue the recording work and the observ tions as completely as; poessible, in order to Increase the fundamental material; b) to establish and apply statistical evaluation methods; c) to carry act additional complementary investigationste up for sm

In order to make

deficiencies and to complete the whole.

The*e points can be detailed am folloesa a)The station network, consisting of seven stations situated at different altitudes, and the instruments used as yet (see section 2 and 3) were kept on; additional atmospheric electric and meteorologioal recordings were started at station Farchant (see below Point 3); see, Table 1. b) As a base for the statistical evaluations of the records we used, on the one, hand, the synoptic charts; 310 such oharts are in our archives till nowl they were made for all days which, owing to their weather conditions, could throw light upon relationships not yet unlerutood. oni the other hand, &"E

recording day was entered into a card index, which enables us to

classify systematically the individual cases and to discriminate betw*eo the different ypoe.. a) With regard to the measurements added under Contract AT 61 (510)-949, we have to mention the precipitation analyses for nitrate and nitrite

-3ions and for the p% - value. These analyses were carried out sytoematical ly and may aomplete the insight into the atnospheric electric processes, especially into those which take place during the formation of rrecipi-

tation. Besides,

station Farchant was enlarged considerably by adding the con-

tinuous registration of air earth current, point discl.rge current, meteorological amagitudes (temperature, relative huzidity, wind velocity) and of the number of positive and negbtive small ions (by means of an instr-ment lont from the Institut fUr Technische Elektronik der Technische, Hochschule Winch-.). T.oe scintific objects of the investigation carried out under Contract ALF F1 (514)-949 are outlined by the following pointso a) behaviour of atmospheric electric magnitudes, studied simaltaneoualy at different altitudes in the range 700 - 3000 a above sealevel, during all types of precipitation; b) electric phenomena during drifting snow; c) behaviour of atmospheric electric magnitudee below and near thunderclouds: d) behaviour of atmospheric electric magnitudes during foohal e) atmospheric electric processes observed at mountain stations when immerging into or coming out of fog; f) electric charges on sheet clouds; g) values of electric conductivity of the air at different altitudes and their dependence on convection, wind direction, atmospheric radioactivity, etc.; r., ,j

trial thunderstorm forecasts by means of spherics records; influence of sm

flares on the frequency of thunderstorms and spherios

pulses k) correlations between nitrate and nitrite conoentratioc and p. value in precipitation, and precipitation type, atmosphtric unstability, and etmospheric electric processes. For some of these studies it

was necessary to know exactly the behaviour

of the atmospheric electric magnitudes at the different levels in fine weather, i.e. the monthly and seasonal meas of their dJurnal variations recorded on fine weather days. Although this part of the numerical evaluations was not one of the main subjectd of the work, we could not do without it; It was made possible SCRAPT. We wish to express through a subsidy of the DEJCEN YNSCHUROSX our thanks for this esential help.

-4-

In the course of the two years covered by this Report, clear that our station network, at different altitudes,

is

method*), c.•ronoue

I.e.

for investigating the behavi-

nagnitudes during precipitation.

Our synoptic

the uniform and simaltaneous comparative evaluation of the syn-

records and observations

tore and in

became quite

being a step-ladder of seven stations situated

specially appropriate

cur of atmospheric electric

it

some other respects.

of all In

the stations,

this

Report,

proved to be suitable

therefore,

the results

from the precipitation studies shall be described with more details

obtained than the

others. It

is the purpose of this

Vound now,

Report to give an insight,

into the atmospheric electric

tudes during different meteorological being taken that the result:c cases,

which Is

more pro -

phonomena observed at different alticonditions and influences,

great care

.-o.ld not only be demonstrated by individual

but expressed quantitatively after

a statistical

evaluation of many

Casne. On the other hand,

it

could not be the purpose of this

and discuss theories for the correlations i.atur*.

found,

Report

to develop

nor to give the existing lite-

Some theoretical studies were already begunl we are intending to carry

them through in

the future, and also to collect further experience and to com-

plete the picture by continuous recording and observations.

I.

RecordJin

Instruments

The Instruments used are described (514)-732-C.

The equipment,

vestigations

carried tout,

a)

purpose,

except the followings

the member of positive and negative small ions

ontinumoasly since October 1957. The apparatus used for this

ale already mentioned,

was lent by the Institut

nik der Technischen Hochachule Minchon; institute

it

applied in

instrument described by WhIslsen und Creutzbora (see

,.dded.

Lar•hs.t,

f¶Ir Toohnische Elektro-

was developed and built by this

*ccording to the same principle am is

b) At

th, recording

WNaleisen

(1957)

also the registration of the point discharge

A "oint at about 6 m above the ground,

made of ctainless

nurpose.

az

recorded by an electronic potentiometer recorder (see

Is

recording results

The point discharge current,

passe,

).

current was

steel (V4U),

,:ced for tni, ifiter,

61

nov proved to be suitable for the in-

was not changed essentially

At station farohant,

hits been recorded

which till

in dotal1 in Technical Report Al

through a simple

we refer to section 14.

+) for more details on this method see Report A? 61 (514)-732-C

below). For

is

-5c) Since fall 1957,

at Farohant the atmospheric electric data (potential

gradient, air earth current,

small ions both siAp,

point discharge current)

have been recorded by mans of an electronic potentiometer recorder (Siemens & Haleke,

Hartmann & Braun).

?alske.

It

Is possible,

To got this intrument as a loan of the firm Siemens &

with this twelve-channel dotted-line recorder,

cord 12 different elements on the seae shoot, being 4 seconds, each ulement. .rfate

thus, if

to re-

the distance of the single points

12 different elements are recorded,

48 seconds for

This electronic potentioneter recorder proved to be very appro-

for our work.

For recording eanmples see figure 1o0.

d) Since January 1957, we habe been able, through a grant of the Allgentine ElectrlcItatagesellsohaft

(AM)

Berlin,

wind velocity, zenith brightness,

to record continuously at Farchant

relative humidity, and temperature with one

point recarder on one sheet. So the comparison of meteorologloal and atmospheric electric curves is made very easy.

3. The Station Network The localities and the number of the stations for the atmospheric electric recordings have not been changed since our Technical Report A.? 61 nevertheless,

(514)-732-C;

for the direct understanding of the statements and results pre-

wented in the following,

it

seeme

useful so give a short survey of the stations

once more. In table 1,

names with *.brevations of the stations are given, further

their altitudes above sea level,

type and beginning of the respective reoordings,

and their geographical situations. In

table 2, we present the relative situations of the stations,

i.e. their

horisontal and vertical distances. Fig. I is

a simple map of the shape of the region and the situation of the

stations. The highest mountain rengse,

extending nearly in

weat-west direction,

is

called VrEWTEINWGIIRCI (Vetterstein Nountains),

is

the ZUQSPrTZZ. The Wetteretain Mountains as well &a Caraisch and our "head-

quartersO Parchant are situated in the nort hers [email protected]

the highest peak of which

4)

CL

a.z

C.

a

-

0 2;

f4-3

3.z

C~C

a

*0... ic

. W

0CL-

.d

.4

0

cc3

0

4

-a

7-

Table 2 Name of the station

Difference in altitude between station and

horizontal distance from

Zugspitzo Peak (Z) Wank Peak (W) feet

Farchant

7514 ;624

()9.0 (50

1.501

(z (w) j6432 ()2.42

varmisch ___

miles

7.

7410

.99 (1

3528

_____

Eibsee

z (w) (z (Z) (z)

Oberno~os

5630

(Z)

2.06

Piffelriss

4530

(Z)

0.93 (Z)

3890

(2)9.01

__________

S N

3

The station network

(Z)L-

19 KM

SMKES

-8a-

4, The behaviour of atmoepleric electric Ksaltudes., observed a~maltepeously at different altitudes, during precipitation

of 01tmoseric elecotric Maltudes on typinga dazqsuerveyed with the hel-p of sZnoptio charts

4.1, Bobshgvio

klthough we shall give a statistical evaluation of the results in section 4.2o and although in Technical Report AF 61 (514)-732-C a numaber of individual Instances have been presented already, it seem" not to be advisable, in this Teo?-aiica.l Report# to omit such individual instance&, whether with respect to precipitation nor to all1 the other problema; there are some reasonst a) Further instructive example* have been collected thes* two yeare. They shall not be withheld from the reader. b) EVery statistical evaluation Is based on simplifyin~g and schematizing procedured applied when observed facts or curvea are translated into significant numbers. With all carefulness It Is within one's discretion to choose the means and methods. T'herefore, we want the reader himself to have the opportunity, by means of the individual cases and originj4 [email protected] of chocking If the elaborated and concentrated results, wich will be given later-ca, represent the circumstances satisfactorily, If essential details are omitted, or If quite different viewpoints could he found with respect to the evaluation. We have still to point to a fact, which must be always considered when looking at our records and their evaluations, in our equipment, the air earth current to always measured with aerials, the aross section of which is so small, that the precipitation charges falling down on the aerial have no significant Influence on the rvcorded values. Thus, during precipitation,, the orgcipitatigg current does not contribute to the measured current, This must be taken into &count, when ou~r results are compared with thode of other investigators (e.g. Chalmers (1956), who m6asures the total current including the precipitation current). In view of our*method it Is not surprising that, in otecordse ohtaimed during precipitation, nearly always current and potenia.l gradient show the same sign* It is nct necessary, therefore, to view the behaviour of current unkd potential gradient separately in our evaluations of records which are obtained durinig precipitation. 40.19 Shover grecipitation

To begin with, let us deal with some examples of light separated showers,, -rer.c-itqd by the rigures 2 - 6. Seldom we find during shower precipitation

-9-

Notes to the

S y n o p t

I c

C h a r

t s

All curves are to be read from right to left. dataaregivenin T i m e

Central

European

- K=). [email protected] of time marks

(CR

one

Monthly means of I and calculated for each of fine weather

At the left

continuous

he

auines

earth current

recorded air

i

houlr.

3 recorded potential gradient i

Time

1

i

light dashed lines

hour a

days

margin in

large circles:

1

abbreviations of the stations (so: tables I and 2 and figure 1)

Below the curveo

**geoG, 1

&uf stations Z and Fo

5•/6;

6/8;

0 7/8;

cloud amount

O0/6,

and species of the cluids abbreviated.

Type and duration of precipitation., are entered in

*

drizzle

Vshower

Intensitiest

snow

*

graup- l

A

rein and snow Smnled

thunderstorm

fog

=strong

istj, etc.

the respective records as followsn

0 rain

-

fog,

=trb.

drifting fog

0 -

(J)disantu 9

thunderstorm

O0 moderate

4* drifting

mist

slightl

hail

I - moderatel

mis*

snow t - strong

F

-10

-

-4aUS

g~~~~

l

M

R

T T

IIL

"LU

-T7

@

---

--

Jill i-4-L

At-a.

A-

on a~~., 87

Fi gre 2 Light aoparatte'

showero

r.

26~~~~=

WZ:

4

6

2

E

A~ 22

M

14

I Wv

~

Jf4.72.

T

w.r P f SolEy

0E obam"I:

m

V

E

I"

0

FS"W VSA

.

i.

we~a--a

Als

Figure. Lihtspaaedsavr

3~

-il

91

7-7-

I.T

TIf

itsf

ad M.

0,

Li~~

El Gei~

:0'*R 0060 F)re

1w

77i *

Ox

..

a

a

ow

0

fbwlf wab70m 4

"W___aAlm"

144

fjf

mw*

Figuria 4 Light separated showers

-

?4 A2

MEZ56

13-

W

V2

8

-jr

Zug***

lo

Z96 ~

A70

~MY.

.

A _

(A min~yw

I

(g

_

E-~f

W

R'

&hm _

_

_

_

_

_

_

-W

_

PD'r9

efmfm

t

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Lif-rýt shower orocipitation with thi.ndcruotov

Ce

15-

-

the sign of the potential gradient to be predominantly the same at all levels (Figure 2).

In much more cases the curve shapea of all

3, 12-14 h; Fit-ure 4 and 6).

other duringe the seae stower (Figure a fact that,

during shower,

levels differ from each Farther,

the transition of the precioitations

it

is

from the solid

into the liqu.d state and vice versa has no influence on the shape of the recorded.curve (Figures slight showers, dient. is

2,3,4).

Studying these and other examples,

especially at station 7ugspitze,

At peek stations for instance,

we notice that

cause a negative potential gra-

a predominantly negative foieign field+)

euperimposed upon the fine weather potential gradient

the "mature stage" of a cumulus cloud is

beginning.

even then already,

when

There 3re many observations

'see below) which show that Auch a negative foreign field exists already before precipitation fal.ing out of the cumulus cloud arrives at the station. Fowever, we &re not able to decide whether formed in

the cloud and is

in

th.ese

cases precipitation

hovering because of anabatic winds,

are great field strengths built up already before (VonLegut In

and Moore (1958)1

Figure

Moore,

has tsen already or whether there

zhe fornation of precipitation

Vonnegut and Botka (1958))

.

5, we see an example of negative foreign fields recorded at

station Zugspitze below Cumulus congestus clouds with the rain being very slight in

each case of negative notch. Already these very slight "showers"

typical alteration of the curve shape with heights rain at high levels,

being quite unsystematical

of light shower precipitations. other phenomenon,

"of the

negative values during the

finally positive ones at low levels.

of the potential gradient,

By the way,

exhibit the

in

Such sign reversals general,

are typical

they must not be confused with an

from which they differ essentially& with the sign reversals

foreign field in

non-showery precipitation , occurring when the phyuical,

state is changed (see sections 4.1.2, 4.2.3.,

4.2.4.).

Light thundery showers do not differ essentially from light nrn-thundery showers

(Figure 6 / Figure 4).

Heavy showers (Figure

7)

differ from light showers only by greater positive

and negative amplitudes of the foreigkn field. of the reosrds at the different stations

is

A corre oadenoe of the course

only seldom observed during heavy

shnwere.

+) "Foreign field" mea,|s precipitationas it

that additional potential

or cloud-charges,

would be in

fine wea

her

is

gradient which,

caused by

superimposed upon the potential gradient

-16

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The variations of the foreign field have especially a-, and,

great amplitudes and

very rapid and frequent during and after cold front pa8ss!Vs (Figures 8 -

12)9

without cold front, also in the case of ocontinuous great unstability of

the atmosphere (Fisue 13).

Alroeady from the individual examples presented we

see that obviously the frequency of the sign reversals of the foreign field 'a the higher, fNrther it

the greater is

the atmospheric lability.

has been observed that, at high altitudes,

t'.e sign reversals of the foreign field is (see

PigureO 13 , which gives an extroe In

eeample).

this section we have to mention a ftrther phenomenon,

statistical

evaluations becomes less menifoet:

stratum Is formed, stratum,

the frequemoy of

somewhat loss than at lower levels

which more and more becomes

If,

( Tigure 11,

19 - 22 h).

The first

by upolide motions,

Alto-

thicker and turns into Wimbo-

the potential gradient at all stations is

far below the fine weather value,

which in the

deorease*

during this process

a long while before precipitation comes down precipitation out of such a Altostratus or

Nimboetratus cloud forued by upelide notion arrives at all stations in a negative potential gradient (V'igure

11,

13,

"hak type of precipitation In falling,

1a.3O).

!t makes no difference,

whether snow, or graujel, or rain etc.

21 - 22 hl Figure 12,

15 h; Figure

4-

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4.1.2. Na-ehewey 4.1.2.1.

Ireolitation Light precipitation out nf Altostratus or Nimbostratus

Lot us begin with individual oases of light precipitation, first such cr.zt of kltostratus. Here the same is true [email protected] was said above about preopi-tation out of Altostratus (see here Figures 14 - 16). The potential gradient is predominantly negative, where precipitation out of Altostratus arrives at the station# whether it be rain or snow. There are also exoeptions, of Oourse (Figure 17)t negative potential gradient at the lower levels in rain, but positive potential gradient in simultanooms *now falling out of Altostratus higher up. Wo point especially also to Figure 141 At 21.00 there were only single drops or trails of precipitation above the station. Nearly always, also iA suoh case* only nogative potential gradient is observed

thus even when

the precipitation doesn't touch upon the ground at the station, but is hovering about It. During light non-showery precipitation out of Cumlus or Nimbostratus clouds we find predominantly positive foreign field at a station where snow is falling, and a negative one at a station where rain or wet snow is falling (Figures 18 - 20). 4.1.2.2. Heavy or continuous precipitation out of Nimbostratus This last statement of section 4.1.2.1.

is true also for heavy or con-

tinuous precipitation out of Nimbostratus. The case of rain at all the stations Is demonstrated in Figure 21, the case of snow at alle the stations in Figure 22. In rain, negative foreign field is by far predominatingl single thin positive points occurring are seldom. In snow. positive foreign field is nredomi-r.tir.g. With respect to snow, however, we have to make a complementary statement, it has been ascertained again and again, without exception, that the base of Nimbostratus carries negative charge, independent of whether snow Is falling, or rain. In cases of no precipitation, therefore, the potential gradient is much lower below the Nimbostratus cloud than in fine weather, mostly between slightly positive and slightly negative. Where there is rain, the "negativity" Is Inoroasedl where there is snow, the positive foreign field caused by the snow-fall Is in competition at stations below the cloud base with the negative foreign field caused by the cloud base. This mean*, that the potential gradient mostly exceeds the fine

wheathor value during dense snow

fall, but Usually reumains below the fine weather value during very slight

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34

-

Figure 22 especilly at stations Parohant and Gar-

misoh, If

falling, only at part of the stations,

snow is

It.er sta1inns, a' lower atmospheric

hirlher up,

there Is

"fioors",

field is prepondoibintly positive at the stations with snow,

then ti% foresig

tut proeorderantly negative at the lower station. where it roe 23 - 27).

while at the

raln at ti,* same time,

VTie is

is

raining (Pigu-

Independent of the height where the transition from

snow ir~to rain takes place, for nastanos whether (at higher levels) between 1isupitze and Wank, or (in the valley) btat *tbsiee n and Parohant. It is in.apendert also of whether

part of the sta'.inis ta within the cloud or not.

The conditions are the seame,

If

change

tg

from snow to rain, and vice but also, at one or more

takes place not only with regard to space,

versa,

Individual stations, with regard to times as field is

ýrepondormantly positive,

!l.,•ures

20 - 31).

Lng an there Is snow,

*s preponderantly negatlve

it

during rain,

the iroing

Periodica& variations of the foreign field curing

4.1.2.3.

precipitat ions In

Figures 52 - 55 we [email protected]* examples

n..aoey that during quiet,

of a case found relatively seldom,

uniform nonshowery precipitation there are sign re-

veraals of the foreign field whioh are not connected with or not caused by a zhane

in &it physical state of the precipitation. These reversals Of

of the

foreign field are nearly rhythotao&l,

Reviewirng synoptically the rec¢rdu of a)

the almost rhytha•oal.

alternating almost regularly.

l1 the stations,

regular weverwala

field are recorded at every station, good temporal

we find t,&o typ.es

of the sips of the toreign

partly even w ih a relatively

g from station to station

ooinoidenoe exitino

(right hand side of Figure 3?2 Ftuzre b

hi* si•p

15);

the reversals are recorded oaly at the valley sta'.ions and tean't show anjy rolatiomhip with the records of the higier stations (right

4.1.2.4. itial iy, b-.!

we

ave to 8m

zovortiesee **mid

I deas.

'4; 4re FICure

hand side of F?4

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t iA

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F mow Figure

28

At at *tjon Zugvpitzot rain is transformed into eno.

F&te

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-48-

more or lees

a) Oucasioasaly,

rapid and frequemt variations of the

for,@iwa field are found durin3 unlfzra rain; espeoially

oftem they take place

within the area of negative values (Figure 36),

,nrves have a tendevoy also t2, poeitive values (Figure in# that this pheoaon

is

the stations exhibit the sa of

tec si•rl.

Thus, in

al

stationns ttoe.

.)tly

37).

sot limited to onlyfstatton, curve oharaoterp

seldom the It

is trik-

but that all

although the variations

differ from sash other in

the frequency.

cases there must be a more than' local cause.

b) Very seld a ve find &A inverse behaviour of the foreign field during non-enowery preoipitstiui, noe-fall Ridfeo. is), at the sa&

oontinuously negative values .,n (Figure 38, statiins Wank and

or positive values during rain, time at amer stations (Figure

c) Very seldom

with negative values possible

39).

it haopens that the transition of rain into enow do*e

not oause a reversal field,

e.g.

(althoW not out of Altoetratuel)

fr%

the negative to the positive sign of the foreign

and vloe versa (provided

ts not Lltootratue).

conditions arp non-ehowery and the cloud

In Figure 40 we see

Waisk and Z~gpltzo positive

that at the stations Riffolriso,

foreign field exists during snow-fall,

at the lovar stations aberwooe,

Kibse0,

earmisch,

and driasle, high positive values are reoordod, the

following transition into snow.

while

and ?archarl during rain toi, snich remain after

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5'4

Table Closd

type

Prooipitation

3 type

Type and number of ase (observed

uniform gaow

sngw

@table

uniform rain

uniform anow Altoetratu mlting snos

Iouniform

rain

Piabostratus

below trails of preoipitation

........

1

toreign field shove sign reversales ... foreign field shows no siag

(upelide olouds); stable etrati fioat ion

reveoealas

.

rain showers ss Istational snow showers Clouds

Stbl ltMaw g Itat is"

ow•de tm ne

mpol fle

n140 eaboes, dulrLng or 0il411111 o

b I fvw-410 flold

110

......... 5

positive fiold, negative foreign foreign field,

.10 165

variations of for.field parallel at more than 2 stational ...... . .-

.16

positive forelgn field, negative foreign field:

53

foreign field shows esgn reversals . foreign field shows no sign reverealas positive f~rre•

3

0 ..

fields

negative foreign fields poaitive foreign fields negative for*ign field,

oheotto oourse of for. field at all stational

un~stable•

1

poeltive foreign fields 177 negative foreign fields.. 11 stational

ml*tia

or Altoesratua being transformed

1 9'S)

variations p ar a.llel at ofntorforfield # than 2

Plalbo st ratu s;

stratification

,S * 1956 +

4 7

.57

2 15

1ý0

variations c,F for.feld parallel at aorv than 2 46 vuriatione of for.field antIPM1a*lel at more them statiors foroe!p field shows tl

4 0

reersalse

foreign field egatveoe ""@Ia• reversals onely mesative for.fteld at setati.n| z""PISee

i

positive foe4p field$ mp0t41w 4p fe•pl. fields

3, 2

4.2. Results of the etatistioal - synojtic evaluations 4.,.

Survey on total numbere

In table 3 a %.urve# it riven,

wi.IcL wAs obtained by nvuboring the cases

of the different typee of potential gradient behaviour during the respactive precipitation and cloud types. For this, our oard index (eeo Intruduction) was used, which now comprises the years 1955,

1956, and 1957.

4.2.2. Snow showers and rain showers For every station ard every precipitation, rate rain or snow period, we oalouated by meane

i.e.

for every oohercnt sepa-

of the "synoptic charts",

during what peroentage of the total pr*cipitat~on duration there was positive foreign field. The total duratiorn of such a precipitatioc period was concidered 10.

Further,

the numbers of sign reversale oi tha foreign field per hour

*ere determined for thi, same precipitation pariods. The fine weather value of the respective hour wd month (see section 15) was the base for the calculation of these two mansitudes; the foreign field Is asv•ed

to be positive,

where the

potential gradient is above the light dashed line entered in the synoptic charts for each station and representing the aversav daily variation per monthi) (see 1957,

foot-note page 15). All our synoptic charts of the years 1955,

1Q6 end

i.e. a total of 310 *ynoptiq charts, were evaluated I!, this manner.

Data ottained dur~ng an excursion to the Zugapit.platt in 1955 (see Technical Report AF 61 (514)-732-C)

were also included.

Then for eaoh of tne stations the arithmetic means of the magnitudes were calculated over all precipitation p#eriode.of the

years, i.e. over the number

of re-ording hours entered at the right hand aergln ox the following figures. In the firures of section 4.2.2. atud 4.2.3., the mean poroenla" 9ef the preolpitation duration, which have positive foreign fight, always ar-idesignated by 1% poeitive* -nd reoressnted by blaok columm,, while the mean numbers of the sign revereale of the foreign field per heur a-e doeegnated by "ohiaes p,ýo. and repreeented ';y white colume. In Figure 41,

the result for rain sh were is gIven aynoptinally for r.ll

st.ations. Th* foreig

fleld dtLring rain shower is positive for U) - 4• 4 )f

the precipitation Juration,

depending oa the stetioi.. The

umber of its sign

reversale per hour it betwees 2. and ý. The IlrKest frequencies of sig. revereals are fowW at %he valley statione. Nrrisg esoe-shwer

(PtFiur* 42),

of the total precipitation diration,

the forvign field to peettive in 40 - 5 k peroeontage which is Set coas•derstaly

Later thm the vaite ftted fer rain ehower. The •uer ) in fine weather

of the reversals po.

VM jrý

AlaWRECIWWO6

HOURS

ME=104

2000

2177 240

-

1000 -

w~j

D'I

.3

244

2 i

Figu&re 41 Foreign

icild and itc sign rsvpr~ials du~ring rain shower

I v

ADMW

~SEA ".~r

N00 RECOR01,,

c;HOUJPS

TO,,

CAM qW1

-

-------

__________ ---

Foreign~ field aji4

Ita otai rversals

1iuriri4

m' momhotvar

1

- 57 -

hour durkng snow shower i1 almost the same as during rain shower (2.2 -

2-7).

Neither in rain shower nor in snow shower an Influence of the altitude of the station on the positive foreign fleld is If

found.

we do not discriminate between the altitudes of the stations,

but

between three atm~spheric "floors" chosen according to the physical state of *he -rec'pitation,

thus

a) snow shower zone b, melting zonc, versa,

wý.ere tUe tranrixtion from snrld to liquid state, or vice

taxes place;

rere showery snow can be mixed with showery rain,

c) rain shower zone, then we obtain Figure 43s

the transition from the snow shower zoe to the

r.elting zone involves a light decrease of tVe positive foreign field peroenta-

ge to s value which is sign reversals

is

the

iame as in the rai

somewhat grate-

in

shower zone. The frequency of

the moltin

zone than in

the two other

zones.

AGORECORDG HOURS

\_

J29

VKf28 -,4"

FA~r*!9qn field a,'

its

~~r~rs5hrn

ahoper in the I~tree "it~

4,2,3. IUg-hoeh

y preo.

A quite different pictuet

itattloaz imuorteroe of tne seltlua

results from se analogous inves•igation of

non-showe"7 precipitatiOns.

During uniform rain (PFegre 44) the positive foreign field peroenta4g

is

only a - 12 %, and the number of s~gn reversals of the for*len field per hour 0.7 - 1.2 . Thus, both magnitudes are smaller than in the case of ralia shower. During uniform snow (Figure 45) the range of the frequencies of sign reversals is about the sam sa during urlform rain, but the positive foreign field percentage

is mob higher than during uniform rain (80 - 90 %).

If we agnla discriminate betweem a) same of umiform anow b) melting sone, whatre the transitaio versa, takes

from solid to liquid statle, or vioe

liae; here snow aea be nixed with rain,

o) some of uniform rain, then we obtain Figure 46. It differs fAwdamentally from ?lour* 43.

In the owre

of son-showery preoipitation*), the melting precess, as to suggested by this Figure 46, to ceupled sith those processes whloh esause the sign revoeial of the forsie

field. If another same were eoupled with those processes,

oolumn of the melting sone would be the same am for ency,

the black

or the someVfor rain,

and not in the middle of the sequ•sOe. We note further that the e-t7 reversals are more frequent in the melting zone than In the snow and the rain sons. There is a simple reason for thist the transition from the rain "floor" to t1,q snow "floor", or viae versa,

involves at least one sign resersal, and these sig

reversals always are added to the sign reversals ooourrir• in too melting zone by other reasons. Beyond this, ia the melting [email protected] eo.reversal* are more probable,

than In the Wo othr'

zones,

6!Ano0

-=-•chnges .. f the p,.,yioal

utats

of the preoipitation are relstivq'y probabhli here. In the ano* eone, sign reversals are sore frequant than In the rain zone,

but auob loes

frequent than

duriL• stw•wre.

16

.CI'WL r* slgibtl) aJr*44

in

tres os..

of eb•bor

preeiy4tstlia

S4A EWLT~~ O0Cf

imAR1

HUR

JJ~G~Tj21

2000

-

WANt(

"M"3 rof

420

soe

__0__

0

Figure 44 Foreign field .a4 its *.on

reversals duaring aco-aokiory rain

*

A8OO17I

SEA LEWk

OURS

~~~O

1O000 araft±

&Alf_

Vorto f1014 aeai Its stjei

__

__3

ul~jfrm-skyw*Iy wa~S 61,09

-60-

NOOF RECORaWG HOURS

331

12M

*

%pe.,,e

,0

iO

U

IWA

10o 2

3

Figure 46 Foreign field and its sign reversals during non-showery precipitation in the three main precipitation zones

4.2.4.

SLre*Axth and sign of the potential ivradient at different altitu4ee durLng rain or snow

For each station,

this analysis was carried out as follows (Figure 47)t

a) For each hour of uniform snow (number of recordi:ag hours entered at the right hand margin of Figure 47 ann marked with "* "), we calculated, what percentage of the fine weather potential gradient (,Lnd conduction current) of this hour and the respective month (see section 15) the jctual potential gradient E (conduction current i) is on the average, the reipoctive fine weather value alway* being iO00. For instanoes

if, the actual con.ýjction cur-ent equals the fine weather oonduotion current of the same hour, the percentage is+1001 ori if

it

is twice the veespetive

fine weather value,

the percentage

iesQOO or, if it is sero, also the percentage is zero. The arithoetic mean of all the potential gradient (conduction current) pereentages is entered in Figure 47 as black (white) colum, and that for each station. All the seven values are far above +100 f. The potential

61

-

-

gradiemt peroentages deorease with increasing altitudo ( oompare oootlom 4.2.6.).

W•lt of the uniform snow cases oould be evaluat-

About

ed syutematioally in this manner. The rest showed so high positive values, thet the devitations surpassed the record sheet breadth;

it hat to

be omitted. Consequently we may assume, that aotuallj the mean peroontages are even higher. b) The soam

oaloulation wae made for uniform rain (number of recording houra

entered at the left margin of Figure 47 and marked with results give lees informatinn, sinoe the range of

4

"

").

Them.

ligtt rain" osnnot

be defined exactly. During strong uniform rain-falls, ou the other hand, usually the breadth of the record sheot was surpeae tation days had to be omitted.

, u- hoee precipi-

If all cases of ýýniform rain were inolu-

ded, the negative mean percentage,

oonsequent:lyj womld be Still more ne-

gative. The differences of the peroentwige

frin ae rtion to stat;.on, are

here only smell.

HEIGHT STATION: A80VE SEA LEVEL 3000-

O OF RECOka'NG FhL/RS

ZUWSPTYUE- 52.

l

*

210

2C,^C

66*

t4 K

3 L'1"97

I-

so 50

RIS

CgTR1.4fXI 60e

46*

-

70o0 -. 'IBSEE -771 e

i43

~37

5 0

FA~I~VT1' 100

10

0

010

I0

*

4

a25* 20

Figure 47 Strength and slgn of the potential gradient at different altitudes during non-obvery rain or snow

00

-

O•I

300 %

-

4

62 -

sig

-Streng~hand

oT' the potential gradient below Altomtrntue

with or without procitation falling out of this Here

we recall, to begin with, that precipitation oUt of

very7 slight. In Figure 48 and 49, fine weather

Oh

is

for each station the mean strene-.1 of the

potentinl gradient below Aloutratu-, e0,

Altostrntus

in terme of percentage.,

Is desonatrat-

o ;entiril gradient being 100 % (end represented by the

vertical deahad lines). The nalculation of the arithmetic meant was sade an described in section 4.2.4. The same analysis was carried out for the conduction w-rent. If there is snow-fall at statio Zugepitzs (Figure 48), t1e p, tontial gradient (conduction cwrrent) nevertbeless is lower than in fine weather. It is about the eau

as in the case of the station being 1e•aov Altostratus with-

out precipitation. However, where there Is rain out of Altostrxtus (Fig•re 48), the values are clearly lower than in the came of the stati. n being below Altootratur without rain (Figura 49). This inveetigation amgan chow" that below Altoetratus the potential gradient is lower then it wuld be in ,eme section A.1.2.1.).

fine weather

Hence we say conclude that the base -f the cloud sheet

ca.rriea negative spasm charge. If eolid precipitation particle* are falling through the Altoetratus, cloud drnplete, which doubtleve carry negative charges, fretsa upon the procipitatica e.rticles at the cloua base. This will prevent the poeitive values of the for•'ign fied, wAie.h are uotal in all tUe other c¢ese ci iam-ehowery precipitatinn, appearVig also in snow fcllinx oeve-al rseorns, w'y thie

out of Altostratus. There can

be

w_-3hin~em Aoeon't tork 3n the case of Nimbostratus,

the base of which carries negative chazget a) Altostratus mostly is only of small thickness. Consequently, the precipitation particle.

formed An it

have still very nmall falling velo-

cities, vrh

tbk.y ar-4.vi at 'he oal",d be-e. Thuethoy have relatively such time available there for picking up nega' 1ve charges. b) The Bies

of A]tostratue, in oontra•2a1tinotlon to that of Mimnbotratue, Ie suLrp and definite. So the negative space char"- density there will

be expecially high. Therefore relatively many negative charge. of freesing-un cloAd droplets are conveyed to %he surfac

of the preoipi.

tation particles just in the last moments of their fall through the cloud, so that the compensation by poeittie cloud droplets freesing on the pteoipitation particles is small. +

t

oornradatinctiaon to the on•i4tione

in Niabcetrutur

-

-

Ei. OW ALTOSTRATUS WITH PR'UCIPITATION

HEIGHT STAT

AO OF" RCORtU'NG hOMX/

ABOVE SEA LEVEL

3000,

63

,

ZJSPITZE.

N

20

m PLAT!

2F

33 2,

OBER__M ZJ_•un

32

0A~1

4•-

I

FAPCp?1NTI

E 0

700

200

400 %

300

Figure 48 Strength and sign of the potential gradient below Altostratus with precipitation falling out of this HEIGHT STATION:

ABOVE

ISEA LEVEL

I BELOW

½::

AL TOSTRATUS

AOOF RL

*"'! .' .'

ý-OROWN 6H DURS•

68

30COC- ZLIGSPITZEE

PIATT

2000•-

WANK 0•TRM 7000L-

33

-

1 3? 27

EI1BSEE

0

IbC

200

300

Figure 49 Strength and sign of the potential gradient belew Altostratus without preoipi1,tion fmaling out of it

400 %

- 64 -

4.2.6. Influence of type and mine of the snow orystale on the strenirth of tie foreign field durIng snow-fall kl,•e*4y Li Technioal Report AF 61 (514)0-72-C

we reported a preliminary

investigation which showed that on the Zugspitte the foreign field in snowfall depends on size end osystal type. This result could now be oonfirmed with a maoh greater number of obeervations. Figure 50 gives, oentagea,

"man yues

in term of per-

obtained for station Zugapitte. The number of snow crystal

obeervatf.ono+) ar.' indicated on the top of each colum.

The

OO

% level

signi-

fies die potential gradient as it wo4ld be, at the hour of the respective observation, in fine weather. The figure ehow* cleoaly that tne potential gredient during snow fall is the greater, the greater Is the diameter (i.e. extent In the largest dimensioq of the snow oryutalu to'raing the snow fall (flakes are ver7 seldom at station Zugspitze). Nurthar, the praotial gradient Is higher in the o"e of flat (e.K.

plate or star shaped) or~ttale than in the case uf

neodle shaped crystals. Perhaps it

[email protected] allowed to Infer from these observations

that thi falling velocity of the precipitation particles It of importance, and so that the foreign field is the stronger, the smaller is the fea•ing velocity of the precipitation pfrtioles. Besides,

Ficure 47 (section 4.2-4.),

*

tV:As view could be oorrotorated by

In falling down, the single snow irystals, which

FI.Ar SOW C STALS

224 OBSERVATIONS 1955

LI NEED.F S

300

1957

• D CIR-STALS

19C %

2

60 O0

(I-

11-2

2-3

3-4

DIAMETER OF SNOW CRYSTALS IN

>4 rpyy

Figurre 50 +)They were made by the observatory ZVgepitse of the oermin Weather Servloe aooordIng to the directions of the U000.

-

65

-

are usual at station Zu~ppitze, more and more combine to form smell flakes and at "sat, arriving in the valley, large flakes. ¶ e latter fall such more Plowly than single crystals, and, indeed, the foreir-' field durino @saw fall is the

stronger the more we go to lower levels.

4.2.7. Relation between lability degree of the stratification and frequency of the mixn reversals of the foreian filid durine precipitation Already by a comparison of Figure 43 with Figure 46 we see that there must be a corelation between tha lability (-unstability) degree of the atmosphere during precipitation and the frequency of sign reversals of the foreign field. Beyond this, it was attempted to grasp this correlation quantitatively. For this purpose, we used the radio Pond* ascent data of the flknich-Hies Airport. The temperature data were entered in the "STMV

Diagram Paperu (observed lapse

rate). The courossof the respctive dry adiabatic an

me:st sAiabatio were de-

termined in the well known smaner. Then the area between 500 ab level line, moist adiabatic, observed lapee rate, and 700 ab line was measured with planimeter. The value thus obtainetd in square centimetres is a relative value for the lability energy between 700 and 5,00 ub. When it

is positive, tbe stratifi-

cation is unstable. These evaluations were made for both radiosonde ascents of each day. Here we have su insert that the radio sonde data are obtained in the free atmosphere, whereas in the region of our station network,

i.e. at a distance of 100 km from Mun~ch-Riem and in the mountains not far from the northern border of the Alps, the actual unatability can be somewhat different from the unstability existing in the free, atmosphere above Uunicli. E.g. we have to consider that in many cases during slightly stable stratification of the free atmosphere there will be already unstable stratification in the mountains, since here the air in the lower atmosphere obtains additional energy by the insolation of slopin

surfaos%.

Figures 5;

-

56 show the correlation which is obtainedl for each of the

stations (Garmisch and Farchant be'.ng united to "valley"), if the frequency of the sign reversals of the foreign field during precii4tation (all kinds) is plotted against the simultaneous relative value of the lability energy between 500 and 700 mb. The etratifioation above our station net, a" mentioned above, is not exactly given by the radio sonde data of Manich-Ries, so we cannot expect the two magnitudes compared to show a very close connection. Hlowever, it is evident that the frequency of sigu reversais increases with increasing

- 66 -

~

STATIO: ZuGSiftrZE-

-

6

I956195

0

o-s

ILg

NEGA Tlb'E

TV

20 i 1? 8 4. 0 LAr ENERGY (RELArI(E m4LUE)

4

8 -

Figura 51 Lailtysergy

between 500 an~d 700 mb v. sign rever-

male of the fora~.g

field during prec.,pitatiozns, Station zueupitto

-

67

-

1 STATIO: WANK

S

135.$7

'C

2".. 20

16

LA

I

12

0

ENEA Vir T V

L~IE

VALE)

SIO -,?E m

Figure 52 t•bility energy between 5M and 700 llb v. sign revi rsale of the foreign field durln• preolpitational Stat ion

Wank

-68-

",~

I9S6 .195

STATION: RIFFELRISS

4

fog

to

soi"r

NEGATr/VE I

i

I

I

PJTIVE I

I

I

Is " 12 "8 0 LAkITY E(ERGV (RELATIVE VALUE) ?Le-d

8 M - 70 #As

53

lability eneoty between 500 mj.d 700 ab v. sign rovermato ýýf the for41i field during prooipitationaI Stetionm Rif'felrieI

69 -

-

10

•,_9

i

9

e9

* %



.

*





o8

0

,

* .

0

00 K-

:..

I!

*-

"

'



*

... .

00

0*

s**0

*I•

8o

0, 1"

Lm

NEGA TIVE' 20

16

12

POSITI VE 0

4

0

LABILITY ENERGY iRELATIVE VALUE)

Lability onargy between 5tO and ca ls

of the, foroeign, field Litati,)ri

lurinX ubersooo

W.?ab v.

5&( - 700 mb

sign rovor-

,r0nlpitattones

I STArio~i

ISMSE #1957

10-

o

K S

Q SS

*al

tS

fS*qw.1

STAION

VALLEY

957,

Ln

10.

4

-0,1

q

*

20

LSILT

is * *

14

bltt

8

ENERG tro

5

35

5

*

0

4

(RLAV 9

*

VAUE 9.

1.

00

S

- 70

- 72 -

unstabillty. 'an imp•ir-tnee.

differences from station to statioa or* ol;

Ts fV'Uo!wizA

ow

s*2sight end of no

be gatbCred from the figurost

If the nmaber of sign rqnerrals per hour is more than I,

it

is very pro-

bable that the stratification of the *tmocphore It unstable between 700 And 5(•) ub.

the fact being taken into acco%mt that a slight negative labllity ener-

gy of the free atmoaphero mostly signifies unatability above •zr r.-uon. tne ather hand,

"he nimber of sign reTersals ps4.our is k.eea thar. 0.8,

assume t!at, with high probability, posesility to aiply this Piz*

the stratification Is stable.

If,

on

s way

es:-6es the

criterion in the meteorologi.al T-ractics,

the

tiestigation is of lnterst also for atmoepheric electricity, because it yieldec. a sort of quantitative rule s'cording to whicfl

%he more or less claotic sign

-eweraals of the foreign field, occurring for instance especially during shower; 4ctually are coupled with the degree of tw-bulacoe. This function.l connection a independent of the orographic conditions and altitudi of the station, it rlects facts of general Importance.

thus

As to the meteorological practice, the results could be used to find out, at a reather station which has no radio sonds and with the help of simple k-cton*;ial gradient recording, if the stratification conditions are changing in the course of a precipitation.

5. The behaviour cf the fcrsaa field during driftin

ancw.

Processes of snow and Ioe crystal friction, of charge septaration by break ing of snow And Ice crystals. etc., are of general interest foir the explanation of tha.nderstorm ale. tricity. Since within our station net drifting snow i. partly changes the electrical conditi•nas

relatively Tr*quent, which

in the nsi-hbourhaod of the rtations

corviderably, a systematical evaluation of the records was carried out wit)' reoDeot to drifting snow. The evaluation was based on t.he observaticn,

that from tha mountain rid-

gee snow and ioe zrystals are whirled aloft many hundreds of metres. This causees Prticles of different Li1es to be separated from each other by th4 wind. The large fragments

iom•

fall b&ao

to the t-rouM,

to týs neigtbourhood of the

place fror where they hat been whirled upi the small fragments, according to circ n•tar.oes, car, wsnder along with the strong wtnd current many kilosetres. In the ermluationý therefore, we 1.-Ato consider above all the wind diro-tion above the Wetteratein Wountains L"ý he geographical elevation of the etatinne. In Figure 57 a little map is added, which gives the main ridges of the Wetter-

No

hK

Mjat S.iio

R

,

74

-

stetrIn Emtais,

-

with station Zuappitse (Z).

Rspeoialy from these ridges the

snow to abIrled up (compare Figaro Q). If tie wind is oomiAq from southern diroctions, the

large fingmente whir57 immiiately

led up at th* -. rthsra ri4je shvun ir. the small ma~p of ?1gure

fall ioack to the slope just north of this ridge, widis e tuially clouds of the small fragments azeocarried away by the wind ov-lr stations kiffalr-'ev (R), bSit&* (E), If,

and xometimes also Obersoce

(0).

the wind ccnew from northern~ dlrectioas. snow to

on the ot'-.r Hand,

vhlrlgd up nea~r the station3, the lsr~rs rertirled. soon fall tack in 'the fle!#hbourhood of the place shere they had boon whirled up, and a certain a*,aatot. of paLrticles of differsnt siz#A takes ;lacei but the smnall patrticles crigiat in~g at E, 0, or I cz.;iot te carr.!*Ie

avar the wall formed by the rýg

of the Zugpitze, and a seppration of the differart kindp cf those particles which are whirled ur at station Z -:ould oal: inf.utnee the atuos,~haric electric codý-Ions at statinns attuatod to the south of Z (which Jomlt exist). are included whire,

In F±ire- 5"7,all ct.Ae a) there TA" fine

esoth~rn anid

b) drifting snow w~t

',baerved at the mountain ridge, and

c) at one or more cf the, stations in question (E, or 0, or R) the pove-ntial grsa-iont had not tha fine weather value. The ftguxe demonstrattc that the foreign fie-ld at sattions 0, K, and R i positive

it

during southern

-toetly is nongrtivo.

vtncds

in noasily allicases,

wh.ile during v'~rthern rindi

T1his seant that the clovets of tiny z~xticles fliyn~g

over the station* predofimazitir.#ly carry R-Mat-t-T# chsarpea, ard that, or. ths3 other '.i'vd,

the 1a1M

~ r~.The

:articles whlrlad up nleer t*-e stations carr- Zea~til*

pesitive f-r9e4n fiolds caused by positive crystal clouds flyirg

aloft with the cr.uth vwtni cflen could býj cbest-fed even at i'tati.=r.a -;rsiach ,-d Fierchar~t,

i.e. at a cz.atanre of FAt least 6.

te 4et'.eý-e1-in Mouithins. hevrs t.e sal &;e±, .aaving

their poptý,Y

a-iles fr:). the. --six, ridge of

cryeal.6e prorarIly toure al-ready w-rap-

chr;7*t on t.-e nuclei ,)f

aix (:urrer;,.. For

re~ir4 exasplens 5cc eactton 1,heresultc.'

tfhcin tL es±at-i.iint that,

If icoi

~-Yyntals

are lzroi-,*n.

i'nail1 splfnters carry pos)itiye c-sr~fsv, a&r( Ihe lergor residues neaiecharrw.'

1s 1:. ajrvsdMfst Vjti-' the

Xc~iýAer &rid 5iranar~ (19',5). at ý"zffl.

It

hr.I:etxp#r-4wsntx of Kur- '199t, an **@us t,

be Ii~r~tt5nt for the theory of thuneer-

- 75-

6. Sign o.

Ohe polZential gradient below and nfar thundercloudB

In Teohni-ai Report AT 6' (514)-732-C,

we deouded from Individual inatane-

as that below the bass of thunderclouds the foreign field predC.Atne.tly is negatIve,

b,tt that it

is positive below a far extending

'irrus ncthuA. This st,-

tement 'e in agreement mith the gener&lly accepted view cn 'no struoure of thundercloule. Including all the thunderstorwa of 3 years Ach ocnured at a hiFh

Table 4,

cf the foreigr- field as it wes

level station, gives an acoount of the behavitou. recorded at the respective station. [email protected] 4 Position of the station with regard to tý" -I,,ud part

noIntain. sta•io): within or b~ielew the bake of the lthebai oftheforeign stttioen below suni-an Ciz-xrus no•ua -aounte&n etation bolcw A-itocuza•us ,1la0•onitus or 0s301abus mountain statitn within or below the base of the Iuicnlznbi or below Cirr-s notihu

oe ees,

type an- number of cases (observed 1955 + 1956 + 1957)

ore Ign. field predoidnantly poxitive, 4 field predominantly negatives 31 foreIgn f oreign foreign feo ign

field predominantly positive, 27 field predominantly negative, 21 field predominantly positives 0 field prodomAnantly negatives 16

cwaotio course of foreign field,

44

that iz 44 cale. tie co'. so of the foreign field was chaotic, so

that :t wa&simpossible to ciecirmins-

t~e d!fferent parts of the thundercloue.

Epecially in heavy procipitation we oftcn fizd a chaotic course of the foreign fteld in and below the thundvrcloud -.s

and in the neighbourhood of the cloud.

The records then are similar to t-oe duzing showers. Ir Figue'e

58 - 60 again 1ixdiv•dual caswe are given. They deunnotrmte anew

that prediominartly a pceltile fo.'-ign field exists below Cirrus nothus, tha t this cloud part carrisa positive charges. that at the hig.

From

Figure 59,

i.e.

further, we learn

level svations the negative sign of the fore.gn field is pre-

dominantly below the base of the thundercloud. , e-tatisticl analytin of the cases oLtaine. codonseue

till

now yielded the results

in Figures 61 and 61. The moaning of the oolnxmo

cribed in section 4.?.2.,

Is the same as des-

only instead of precipitation periods we ha"

hpve

?erioda where the station is beliw the aloud part Ineioated at ths top of the figure.

76

-

1

AE' 6'

14

A1*a-4" -

V

Okh

A

-

X

3

4-uý-i

A

X

~&

ID

S PC

*igG Ok

It

TIT

W

Aid s

(i'Nk* Z

®R4M

w

!C'!!-'

4

Z6

z

vfl

23. 780

W

&M*70A

M

N

&,065mA

4W

0

i-

Wef&,ter*, -N.v'z

Figure 58 iPositive foreiimr

field below Cirruas nothus

-

77

-

_

JO,

-

S

_M~m

20

00d Liue5 oreii. Posiive feldbelo

ngativ fild and foregn baa.~ h~ ~~ 'foek

Cirjajnaiu

Sito~mu beow C onyaueiz ~~^-krn

1ik.airi

- 78 -

1-+-+ -4a

Aw1_e8) . IS

_1 a

ti•T! At,,.:: aa-L La U

'

*ai

S

,

4'

AbeO

A1ur6

forqm~~,vvn ftl 1-fP)osmman0Itiv fOrigN aiel

(Fo~ltUea

eo t~tmntu below *mm~ nt~a

-

0,-

-

SrAT~.• SNFPG*/T ABOVE

BELOW

79 -

NIOF'RECORONVG HOURS

Cb - NOTHUS

SEA LEVFL

300

ZLIGSpVT

------------

-

__

___

_it

2000 WANK R

I

s 17

-a

ESE

_

_

17

_

13

2,

0o

o

60

2

1

3

I 9c

0oo

Figuire 61 Foreign field and its

H EIGHr STArlot: ABOVE SEA LEVE-L

BELOW RASE

sigr reversals below Cirrus nothus

.7F

NQOF RECOROMG HOURS

Cb

PLA TT

tiO

Cerfr.

-

-

%

,

0.o,,.40s -

60

.o

ch&uhf Ah Figure 62

Foreign field and its sign reverALu telow Cumulonimbus baae

---- -- -

17

1oo

At first lot ua 1ook at ths stations Zugepitze and. Zu~apittplattt notbas the foreign field Is positive during about 80

voelow CI.-ris

the tir'e, below the Cumu.omnibnn base it

-

90

% of'

is positive during only 20$ of the

time. If we look at the other stations, the value Is about 60 % elholw Cirrus noturs, anid abbut 30 - 50 %below the Cumulonimbus bmaL*, the decreane and increase with height between the valley and 30CM a above sealevel the [email protected] are Influetacad in ruah a mannior that, at the low level stations, it Is no luger possible to lraW reliably an i~nferonce from the record as tc the actual cloue, charge. Therefore records, wich one obtaines only at low levels, cannot yield any satisfaotory resulte with respect to tn* investigation of the thaindercoeud structure. Further we lenin from Figure 62 that the frequency of the sig;1 reversals of tne fireigri field below a Cumaulonimbus base is such greater at lowev lcmele than at higher levels. Fr.om this we nave again to inIX~r thatt the low level rea-'e~ don't enable us to &scertain the temporal and, what is the consoatuenoe, the epatIal charge conditions in the jloud. Thus electrical proceesee are occurring at the lower level.,

which mask the true picture of the

cocnditions in the Cuiuminiu~s cloud. Prnobably the processes in question are con eaoled on the one hand with the pr~cipit*Lion, and en. the other hand with space charges near the ground, whl