An Introduction to Atmospheric Radiation - K.N. Liou, Academic Press. •
Atmospheric Science: An Introductory Survey –J.M. Wallce and P.V. Hobbs,.
Academic ...
Lecture-2
Objectives • Clouds and the energy cycle • Electromagnetic radiation • Concepts of Scattering and absorption
Reference books • An Introduction to Atmospheric Radiation - K.N. Liou, Academic Press. • Atmospheric Science: An Introductory Survey –J.M. Wallce and P.V. Hobbs, Academic Press
Clouds and the energy cycle
High Clouds
Low Clouds
Deep Convective Clouds
5
6
7
Vertical profiles of cloud droplet size distribution observed in continental and maritime clouds
9
4000 June 15
Height above CB (m)
3500
June 16
3000
June 22
2500 2000 1500 1000 500 0
(d) 0
5
10 Reff (m)
15
A cloud with a greater number of small droplets has more reflective surface area than a cloud of the same volume with fewer large droplets. Therefore, aerosols increase the reflective surface area of the cloud by acting as condensation nuclei. This is the first indirect effect, or Twomey Effect.
Same volume, more surface area
Clouds precipitate when droplets collide and coalesce. If droplet size is smaller because of increased aerosols, then the clouds will not precipitate as much. If the cloud does not precipitate, then it retains its water, lasts longer, and becomes larger and more reflective. This is the second indirect effect.
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Detecting and Quantifying AIE Cloud
Aerosol
(CDNC, LWC, re ff )
(number conc., CCN) At constant LWC
Changes in cloud parameters (CDNC, reff ) as a function of changes in CCN and its proxies
_ d ln re d ln Na
d ln Nc d ln Na CCN proxies
7000
Cloud droplet Reff, Size distribution, LWC
Height, m
6000
5000
H
4000
3000
HW(g/m3) CDP_LWC[g/m3]
2000 0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
-3
HW (gm )
Updraft
Aerosol, CCN Cycle below cloud base
3.5
3.0 8000
June 16, 2009
7000
Hyderabad
6000
2.0
5000
1.5
Altitude, m
-3
CDP LWC (g/m )
2.5
1.0
0.5
4000 3000 2000
CDP LWC=1.06*HW LWC+0.03 R=0.92, N=515, P
