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January 2001

Jim Hurrell receives AMS Meisinger Award

Jim Hurrell. (Photos by Carlye Calvin.)

At the American Meteorological Society's 81st annual meeting in Albuquerque later this month, Jim Hurrell (CGD) will receive the 2001 Clarence Leroy Meisinger Award, one of the highest honors granted by the AMS. The award is presented each year to a scientist whose research achievement "is at least in part aerological [pertaining to all levels of the atmosphere] in character and concerns the observation, theory, and modeling of atmospheric motion on all scales."

Jim joined NCAR in 1990 as a visiting scientist and became a Scientist III in CGD's Climate Analysis Section in 1998. His research interests include analysis and diagnosis of observed climate variability and the role of anthropogenic climate change. Jim has written extensively on the North Atlantic Oscillation and on discrepancies in global temperatures measured by surface stations and by satellites. He has contributed to the Intergovernmental Panel on Climate Change (IPCC) assessments and is actively involved in the international research program on Climate Variability and Predictability (CLIVAR); Jim serves on the U.S. CLIVAR Scientific Steering Committee and is a cochair of the U.S. CLIVAR Atlantic Implementation Panel. The author or coauthor of more than 30 peer-reviewed papers, Jim received the NCAR Outstanding Publication Award in 1997. Jim completed his bachelor's degree in mathematics and earth science at the University of Indianapolis and his master's and doctoral degrees in atmospheric science at Purdue University.

Two other Meisinger Award winners have come from NCAR in the last five years: Clara Deser (1999) and Chin-Hoh Moeng (1997).

Next month's Science Briefing will include more news from the AMS meeting, including another major honor: the Cleveland Abbe Award, which is going to Rit Carbone (MMM).

Fuel for tropical thunderstorms on the increase

Andrew Gettelman.

A new study of weather over the last 40 years points toward an increase in the convective energy that fuels tropical showers and thunderstorms. The shift, perhaps a sign of global climate change, also shows up in a simulation of the same period from the NCAR Climate System Model (CSM).

Andrew Gettelman, an ASP postdoctoral researcher based in CGD, discovered the shift while analyzing data collected daily from surface weather stations and radiosondes (weather balloons) across the tropics. Working with Dian Seidel (formerly Dian Gaffen, of NOAA), Matt Wheeler (formerly ASP, now at Australia's Bureau of Meteorology Research Center), and Rebecca Ross (NOAA), Andrew chose 19 stations that had solid long-term records between 1958 and 1998.

The group adjusted the long-term record for consistency between older, human-operated surface stations and newer automated ones. They then used the data to calculate a simplified version of the index known as convective available potential energy, or CAPE. Large values of CAPE indicates that the near-ground atmosphere is relatively warm and/or moist while upper levels are relatively cool. This set-up leads to more intense showers and thunderstorms if and when they form.

"Several stations show evidence of long-term increases in CAPE, particularly in the western Pacific Ocean," says Andrew. Nine of the 19 stations had consistent and homogenous records. Of these, 8 stations had increasing CAPE over 40 years and only one station had a decrease in CAPE. Most of the CAPE increases appear to be related to increased surface moisture rather than a steepened temperature drop with height.

The long-term observations are backed up by a CSM simulation of 20th-century climate. The model output reveals a general increase in CAPE averaged monthly across the tropics for the 1958-98 period. However, the modeled CAPE showed a smaller overall increase than the observational data when the latter was averaged monthly in similar fashion.

Convection is hard to portray accurately in global climate models, so the fact that the model produced realistic CAPE is important, says Andrew. "In order to get the precipitation right, you've got to get the CAPE right. It's a critical tool for making sure that climate models can actually simulate changes in the atmosphere." The bottom line, according to Andrew, is that "the model is able to broadly represent the changes in CAPE observed in the tropical atmosphere, but it may not get the magnitude or the spatial details of the changes correct." Since a rise in CAPE implies increased energy transport and perhaps increased rainfall in the tropics, "CAPE may be a sensitive indicator of global climate change."


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Last revised: Mon Jan 22 15:24:15 MST 2001