Head in a Cloud

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Ice Crystals and their Formations

April 23rd, 2008 by bcote1 · 1 Comment

From the young child trying to figure out why there are no two snowflakes that look exactly the same to the scientist who attempts to answer such questions, ice has been a fascination to anyone who has seen it. The physics behind the delicate shapes has been a great source of study. Such historical figures as Yohannes Kepler and René Descartes have helped to advance this field of research. It is strange to think that such a small thing as a snowflake can bring about such incredible science as was evident in the article “Snow and Ice Crystals” by Yoshinori Furukawa and John S. Wettlaufer from the journal Physics Today (December 2007). [Read more →]

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“Growth of Cloud Droplets by Turbulent Collision–Coalescence”

April 16th, 2008 by Karissa Sanford · No Comments

To help better explain the gap between theoretical and observed precipitation droplet growth times, Xue et al. attempted to quantify the effects of turbulent motions on collision and coalescence. In “Growth of Cloud Droplets by Turbulent Collision-Coalescence” from the February 2008 Journal of the Atmospheric Sciences, several different model parameterizations for collision kernels were compared in attempt to more accurately portray the time span of droplet growth. Prior to this study, numerous attempts had been made to overcome this deficiency. At first, most used a qualitative approach. When others tried a quantitative approach, they failed to take into account things such as the gravitational force in addition to turbulence, and fell short.

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The Influence of Changes in Cloud Cover on Recent Surface Temperature Trends in the Arctic

April 4th, 2008 by cgdenver · 1 Comment

Atmospheric circulation and the global energy budget are largely influenced by surface temperature. Thompson and Wallace (1998) showed that the Arctic Oscillation (AO) is the principal component of the Northern Hemisphere sea level pressure poleward of 20°N and Thompson et al (2000) showed that the AO accounts for as much as 50% of the winter warming over Eurasia due to warm air advection. Rigor et al (2000) showed that the AO accounts for 74% of the warming over the eastern Arctic Ocean and 14% of the cooling over the western Arctic during the winter.

Surface temperature changes are also related to sea ice cover. Cavalieri et al (2003) showed a decrease of total Arctic sea ice extent of about 36000 km/yr from 1979-2002. Studies shown by Parkinson et al (1999) and Parkinson and Cavalieri (2002) show similar results. Sea ice becomes important in a discussion of surface temperature because of a high albedo and associated feedback effects. Decreasing sea ice cover creates larger areas of open water and the varying atmospheric circulation changes moisture advection into the Arctic. Wang and Key (2005) show trends that the Arctic has become cloudier in spring and summer but less cloudy in winter. Trends in cloud amount have an impact on trends of surface temperature. Yinghui Liu, Jeffrey R. Key, and Xuanji Wang quantify the influence of changes in Arctic cloud cover on the surface temperature trend in their Journal of Climate article “The Influence of Changes in Cloud Cover on Recent Surface Temperature Trends in the Arctic” Volume 21 Issue 4 (February 2008).

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Pollution may increase summertime rainfall

March 31st, 2008 by obrien · 1 Comment

In the article “Midweek increase in U.S. summer rain and storm heights suggests air pollution invigorates rainstorms” printed in the Journal of Geophysical Research, Bell et al. make a strong case that air pollution plays a role in changing both precipitation coverage and intensity during summer afternoon thunderstorms. Pollution aerosols act to delay precipitation in a building thunderstorm, which allows the clouds to develop to a higher altitude. When cloud droplets reach these higher, and colder, altitudes they can freeze thereby releasing latent heat and strengthening the updrafts. This can delay the start of precipitation and the development of downdrafts with can allow the cloud to continue to grow. These processes are stronger in a moist, unstable atmosphere so the precipitation changes are best observed over the southeast U.S. Interestingly there is a weakened correlation between pollution and rainfall over the southwest U.S. and some research shows that the increase in convection due to pollution is less in drier conditions and pollution may even inhibit convection in drier climates.
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Effects of Absorbing Aerosols on Cloud Absorption and Forcing

March 25th, 2008 by rplath · No Comments

It would be assumed that in the exploration of the albedo and forcing ratios of pure clouds, one would attain values equal to 1.0. This being the case, how would an observer go about explaining an albedo ranging from .7 to .8 or a cloud forcing ratio consisting of 1.5? These two aberrations have been discussed and observed throughout the duration of multiple studies. Solar absorbing aerosols within cloud droplets have been the accused perpetrators of these results since 1969, yet, no finite conclusion has been accepted. Carynelisa Erlick and Dana Schlesinger study the effect of supermicron dust and soot particles in the American Meteorology Society Journal article entitled “Another Look at the Influence of Absorbing Aerosols in Drops on Cloud Absorption: Large Aerosols.” The purpose of this study is to uncover whether of not absorbing aerosols are really to blame for lower cloud albedos and heightened forcing ratios (the difference between the radiation budget for cloudy and clear days).

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