Weekly Report for the Week of May 5, 2008
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CODE 613 LABORATORY FOR ATMOSPHERES
Papers Published
Munchak, S. J., and A. Tokay (613.1/JCET), 2008: Retrieval of raindrop size distribution from simulated dual frequency radar measurements. J. Appl. Meteor. Climatology, 47, 223-239.
Tokay, A. (JCET/613.1), P. G. Bashor, E. Habib, and T. Kasparis, 2008: Raindrop size distribution measurements in tropical cyclones. Mon. Wea. Rev., 136, 1669-1685.
Marshak, A. (613.2), Wen, G., Coakley, J., Jr., Remer, L. (613.2), Loeb, N. G., Cahalan, R. F. (613.2), A simple model for the cloud adjacency effect and the apparent bluing of aerosols near clouds, J. Geophys. Res., 113, D14S17, doi:10.1029/2007JD009196, 2008
Kotchenova, S. Y.; Vermote, E. F.; Levy, R.; Lyapustin, A., Radiative transfer codes for atmospheric correction and aerosol retrieval: intercomparison study, App. Opt., 47(13), pp. 2215-2226, 2008.
Papers Accepted
Habib, E., C. G. Malakpet, A. Tokay (613.1/JCET), and P. A. Kucera, 2008: Sensitivity of streamflow simulations to temporal variability and estimation of Z-R relationships. J. Hydrological Eng. (accepted for publication).
Papers Submitted
Tokay, A. (613.1/JCET), P. Hartmann, A. Battaglia, K. S. Gage, W. L. Clark, and C. R. Williams, 2008: A field study of reflectivity and Z-R relations using vertically pointing radars and disdrometers. J. Atmos. Oceanic Technol., (submitted).
News Items
For the 4th time in 6 years, NASA's Earth Observatory (responsible NASA official; L. Remer (613.2); Webmaster G. Halusa (613.2/SSAI)), won a People's Voice Webby Award. Competing in the Science category, the Earth Observatory bested the likes of Nature and the Jet Propulsion Laboratory. The Earth Observatory team would like to thank the amazing scientists and staff who make our work possible.
Satellite Data Links Increased Hurricane Rainfall to Expansion of Warm Pool in the North Atlantic
Using satellite data, Lau (613) et al. (2008) found a significant correlation between the increased hurricane/tropical cyclone (TC) contribution to extreme rain events and the expansion of the warm pool. This image illustrates such a correlation. In the upper panel, blue lines show the TC-rain contribution to the top 10% (T10) extreme rain and the orange lines show the evolution of the warm pool area in the North Atlantic Ocean (20oW–90oW, 10oN–40oN) for the TC season (July–November, JASON) from 1979 to 2005. Here, we define warm pool as a region of sea surface temperature (SST) warmer than 28oC. The year-to-year percentage changes are shown in thin lines, and the 5-year running means in thick lines. Rainfall data are from GPCP and TRMM, and SST data are from the Hadley Center.
The fractional contribution of TC-rain shows a pronounced upward trend, indicating a nearly doubling in TC contribution to extreme rain amount from the pre-1992 to the post-1992 periods. The long-term variation tracks well the percentage increase in the area of the warm pool during the data period. The expansion of the warm pool in the North Atlantic is further depicted in the two lower panels, showing average SST patterns for JASON of the first half (1979–1991) and the second half (1993–2005) time periods, respectively. The extent of the warm pool in the second time period is about 20% more than that of the first time period.
Also found in the same study is a slower rate of expansion of the warm pool and a less significant trend in TC contribution to extreme rain in the western North Pacific compared to those of the North Atlantic.
More details can be found in the paper "Have Tropical Cyclones Been Feeding More Extreme Rainfall" recently submitted to the Journal of Geophysical Research by William Lau, Yaping Zhou, and H.-T. Wu. Please contact the authors directly for the manuscript.
Seminars
Freezing of Supercooled Water Droplets
Alexander Kostinski
Michigan Tech
Abstract
Supercooled water is a metastable thermodynamic state and, therefore, the associated phase transition (to ice) must be irreversible. Has this irreversibility been properly addressed? Does it really matter to an atmospheric scientist? I'll argue No and Yes, respectively.
We use measured temperature-dependent heat capacities of supercooled water and ice to calculate the ice-(metastable) water entropy difference and to estimate a lower bound on the amount of latent heat, liberated by the freezing droplets. The calculation is compared with tabulated values of the latent heat of fusion with surprising results. Based on a novel physical picture of the freezing process, we suggest a simple estimate for the effective latent heat, suitable for heat budget calculations of glaciating clouds. In addition, we arrive at a quadratic dependence on supercooling for the irreversible contribution to heat exchange during the freezing process. Implications for optical properties of the "hurriedly made ice" will also be discussed.
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