HR: 14:45h
AN: GC52A-05    [PDF]
TI: Continental Summer Dryness in the New GFDL Climate Model
AU: * Findell, K L
EM: klf@gfdl.noaa.gov
AF: Geophysical Fluid Dynamics Lab, Princeton University, P.O. Box 308, Princeton, NJ 08542 United States
AU: Delworth, T L
EM: td@gfdl.noaa.gov
AF: Geophysical Fluid Dynamics Lab, Princeton University, P.O. Box 308, Princeton, NJ 08542 United States
AB: In this work, we revisit the question of continental summer drying in a doubled-CO2 environment using the latest version of the Geophysical Fluid Dynamics Labs (GFDL) model of the atmosphere and land surface coupled to a mixed layer (slab) ocean. Two highly significant differences between this new model and earlier GFDL models are the increased resolution (2.5$\deg$ longitude x 2.0$\deg$ latitude and 17 vertical levels vs. 3.75$\deg$ longitude x 2.25$\deg$ latitude and 14 vertical levels for the previous model), and the inclusion of both a diurnal cycle and a seasonal cycle (the earlier models only had the latter). Results from these earlier models showed, among other things, an increase in wintertime rainfall over most mid-latitude continental regions when CO2 is doubled, an earlier snowmelt season and onset of springtime evaporation, and a higher ratio of evaporation to precipitation in summer. These factors led to large-scale increases in soil moisture in winter and decreases in summer in mid-latitudes in the doubled-CO2 experiment. The new model shows similar results, and the processes discussed above are important in this model as well. In addition, we find that changes in atmospheric circulation are playing an important role in regional hydrologic changes, particularly in Western Europe. Additional experiments have been run to isolate the feedback from the land surface from the role of the atmospheric changes caused by the doubling of CO2. These simulations show that the CO2 impacts alone explain the majority of the results, while the land surface feedbacks serve to strengthen the observed signals. Experiments to isolate the role of the CO2-induced changes to the sea surface temperature on the atmospheric circulation are currently underway.
DE: 1600 GLOBAL CHANGE (New category)
DE: 1620 Climate dynamics (3309)
DE: 1866 Soil moisture
DE: 3309 Climatology (1620)
SC: Global Climate Change [GC]
MN: 2003 Fall Meeting