Hail, defined as precipitation of balls or irregular lumps of ice produced by storm clouds, forms when liquid drops freeze at altitudes above a threshold called the "freezing level height". If drops cannot be formed above the freezing level, precipitation will remain in a liquid state. To determine whether precipitation trends in hail have changed on regional scales, Xie et al. study an extensive data set of more than 753 stations over China, compiled by China's National Meteorological Information Center. To ensure a continuous data record, the authors choose 523 stations with complete observations from 1960 to 2005. For each year, the authors calculate the average "annual hail days" (AHD), which is the average amount of days each year when hail occurred at each station. Analysis reveals that while there is no trend in the mean AHD from 1960 to early 1980, China's AHD reduces thereafter from about 2 days to less than 1 day each year. The authors expect that this drop in hail precipitation is due to a rising trend in freezing level height.
Trends in hail in China during 1960?
Baoguo Xie and Qinghong Zhang: Department of Atmospheric Science, School of Physics, Beijing, China;
Yuqing Wang: Department of Meteorology and International Pacific Research Center, University of Hawai'i at Manoa, Honolulu, Hawaii, U.S.A.
Geophysical Research Letters (GRL) paper 10.1029/2008GL034067, 2008; http://dx.doi.org/10.1029/2008GL034067
3. Mapping Venus's winds
Venus's lower atmosphere is dominated by cloud and haze layers that span 30?? kilometers (19-43 miles) in altitude. The rudimentary structure within these layers has been measured by numerous spacecraft and ground-based telescopes, which found strong flows directed westward along lines of latitude
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American Geophysical Union