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Harry T. Ochs III and C. S. Yao

Abstract

The numerical methods necessary for the application of moment-conserving techniques to the study of warm rain microphysical processes in an Eulerian mass coordinate are described. When this technique is applied to simulations of condensation, collection and breakup the total drop distribution is divided into a number of Eulerian categories and three quantities pertaining to the drops within each category are retained between integration time steps. These three numbers are related to the drop concentration, the mean drop size and the standard deviation about this mean size. These techniques serve to minimize numerical spreading which would otherwise lead to the premature development of precipitation sized particles in a detailed microphysical simulation.

A picewise linear mass coordinate in conjunction with the moment-conserving techniques. allows conservation of cloud condensation nuclei and water mass to within computer truncation error. Methods for tracing the nuclei mass through the condensation, collection and breakup processes in saturated and sub-saturated air are developed.

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T. Yao, Howard J. Freeland, and Lawrence A. Mysak

Abstract

Six current-meter mooring were deployed in a line approximately 600 km in length along the continental shelf of British Columbia. Analysis of the low frequency (periods exceeding a day) fluctuations in current for the winter 1981–82 period is discussed. Alongshore currents off Vancouver Island are mutually correlated with time lag less than a day. The region of mutual correlation does not extend north of Vancouver Island, across Queen Charlotte Sound. Coherence is observed between currents south and north of Queen Charlotte Sound only in a frequency band where there is mutual coherence with local wind. A comparison is made between observation and free coastal-trapped wave theory. Off northern Vancouver Island, where the shelf is narrower than off southern Vancouver Island, there is increased vertical shear, a feature of the second coastal-trapped wave mode. A consistency test is applied using the cross spectral matrix of alongshore components of velocity. In the dominant energy-containing frequency bands (periods ≳10 days), the structure of alongshore currents off Vancouver Island is consistent with the two lowest free coastal-trapped wave modes locked in phase.

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Jing Gao, V. Masson-Delmotte, T. Yao, L. Tian, C. Risi, and G. Hoffmann

Abstract

Measurements of precipitation isotopic composition have been conducted on a daily basis for 1 yr at Bomi, in the southeast Tibetan Plateau, an area affected by the interaction of the southwest monsoon, the westerlies, and Tibetan high pressure systems, as well as at Lhasa, situated west of Bomi. The measured isotope signals are analyzed both on an event basis and on a seasonal scale using available meteorological information and airmass trajectories. The processes driving daily and seasonal isotopic variability are investigated using multidecadal climate simulations forced by twentieth-century boundary conditions and conducted with two different isotopic atmospheric general circulation models [the isotopic version of the Laboratoire de Météorologie Dynamique GCM (LMDZiso) and the ECHAM4iso model]. Both models use specific nudging techniques to mimic observed atmospheric circulation fields. The models simulate a wet and cold bias on the Tibetan Plateau together with a dry bias in its southern part. A zoomed LMDZ simulation conducted with ~50-km local spatial resolution dramatically improves the simulation of isotopic compositions of precipitation on the Tibetan Plateau. Simulated water isotope fields are compared with new data and with previous observations, and regional differences in moisture origins are analyzed using back-trajectories. Here, the focus is on relationships between the water isotopes and climate variables on an event and seasonal scale and in terms of spatial and altitudinal isotopic gradients. Enhancing the spatial resolution is crucial for improving the simulation of the precipitation isotopic composition.

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Gavin A. Schmidt, Reto Ruedy, James E. Hansen, Igor Aleinov, Nadine Bell, Mike Bauer, Susanne Bauer, Brian Cairns, Vittorio Canuto, Ye Cheng, Anthony Del Genio, Greg Faluvegi, Andrew D. Friend, Tim M. Hall, Yongyun Hu, Max Kelley, Nancy Y. Kiang, Dorothy Koch, Andy A. Lacis, Jean Lerner, Ken K. Lo, Ron L. Miller, Larissa Nazarenko, Valdar Oinas, Jan Perlwitz, Judith Perlwitz, David Rind, Anastasia Romanou, Gary L. Russell, Makiko Sato, Drew T. Shindell, Peter H. Stone, Shan Sun, Nick Tausnev, Duane Thresher, and Mao-Sung Yao

Abstract

A full description of the ModelE version of the Goddard Institute for Space Studies (GISS) atmospheric general circulation model (GCM) and results are presented for present-day climate simulations (ca. 1979). This version is a complete rewrite of previous models incorporating numerous improvements in basic physics, the stratospheric circulation, and forcing fields. Notable changes include the following: the model top is now above the stratopause, the number of vertical layers has increased, a new cloud microphysical scheme is used, vegetation biophysics now incorporates a sensitivity to humidity, atmospheric turbulence is calculated over the whole column, and new land snow and lake schemes are introduced. The performance of the model using three configurations with different horizontal and vertical resolutions is compared to quality-controlled in situ data, remotely sensed and reanalysis products. Overall, significant improvements over previous models are seen, particularly in upper-atmosphere temperatures and winds, cloud heights, precipitation, and sea level pressure. Data–model comparisons continue, however, to highlight persistent problems in the marine stratocumulus regions.

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