HR: 1340h
AN: A53B-0899    [Abstracts]
TI: Reliability of ECMWF reanalysis temperatures and climate change on the Tibetan Plateau
AU: * Serreze, M C
EM: serreze@nsidc.org
AF: CIRES/National Snow and Ice Data Center, University of Colorado 449 UCB, Boulder, CO 80309-0449 United States
AU: Frauenfeld, O W
EM: oliverf@kryos.colorado.edu
AF: CIRES/National Snow and Ice Data Center, University of Colorado 449 UCB, Boulder, CO 80309-0449 United States
AU: Zhang, T
EM: tzhang@nsidc.org
AF: CIRES/National Snow and Ice Data Center, University of Colorado 449 UCB, Boulder, CO 80309-0449 United States
AU: Zhang, T
EM: tzhang@nsidc.org
AF: Institute of Plateau Meteorology, China Meteorological Administration, Chengdu, 610000 China
AB: A significant limiting factor in assessing climate variability over the Tibetan Plateau (TP) is the sparse network of meteorological stations. A potentially valuable source of continuous long-term data for this region is provided by atmospheric reanalyses, such as the European Center for Medium Range Weather Forecasts ERA-40 effort. Here the quality of ERA-40 depictions of 2-m air temperature over the TP is examined. Evaluations rely on a data set of surface air temperatures for 161 stations obtained from the Institute of Plateau Meteorology at Chengdu, China Meteorological Administration. Our focus is on monthly temperature means and time series for ERA-40 grid cells within which there are at least four stations. This provides for reasonable grid cell estimates of temperature through averaging the station values. As assessed from means over the time series of common data coverage (September 1957-December 2000), ERA-40 temperatures are consistently low, by as much as $7\deg$C. Low biases are also present for individual months. However, correlations between monthly grid cell time series are quite high, indicating that ERA-40 captures interannual variability well. Furthermore, the temperature biases are almost entirely due to differences between the elevation of the ERA-40 grid cells and the average of the station elevations. The ERA-40 system does assimilate surface temperature observations from SYNOP reports. Efforts are underway to determine the extent to which these data are being used over the topographically complex TP, which bears on the applicability of our findings to the very data sparse western part of the plateau. Nonetheless, ERA-40 temperatures provide a surprisingly accurate depiction of temperature variability on the TP and can therefore be reliably used in climate studies, such as assessments of long-term variability in the Asian monsoon system. Interestingly, while the station data indicate a long-term upward trend in plateau temperatures, no trend is evident in the ERA-40 time series. This could reflect shortcomings in the ERA-40 reanalysis related to temporal changes in the amount and quality of assimilation data. However, since meteorological stations are located in low-lying populated areas whereas ERA-40 more reliably provides averaged plateau-wide temperatures, it could also suggest that reported climate change on the TP is due to urbanization and land use change in the vicinity of populated regions.
DE: 3322 Land/atmosphere interactions
DE: 3329 Mesoscale meteorology
DE: 3309 Climatology (1620)
DE: 1803 Anthropogenic effects
DE: 1610 Atmosphere (0315, 0325)
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting