11-15 December 1995
From atmospheric tides rolling dozens of miles above the earth to ice sheets ranging across Antarctica, a vast range of phenomena is studied by scientists at the National Center for Atmospheric Research (NCAR), based in Boulder, Colorado. New findings will be presented by NCAR scientists at the fall meeting of the America Geophysical Union December 11-15 in San Francisco. Below is a sampling. Consult the AGU meeting guide for more details and a map of meeting rooms. Times below are the session starting times. NCAR is operated by the University Corporation for Atmospheric Research under sponsorship of the National Science Foundation.
Western U.S. surface hydrology is directly influenced by topography. Sharp, elevation-dependent precipitation gradients result in large differences over short horizontal distances. A three-year regional simulation (1989-92) was conducted with the NCAR regional climate model at a 50-kilometer resolution. The model includes a surface physics/soil hydrology package. Emphasized in this analysis, which compares model results with available observations, are the relations between elevation and latitude in precipitation, snow water equivalents, and runoff.
The authors study the effect of changes in daily and interannual variability of temperature and precipitation on wheat yields simulated by the Clouds and Earth's Radiant Energy System (CERES)- Wheat model. For Topeka, Kansas, where soil moisture does not limit wheat growth, mean yield decreased as precipitation variability increased, while the yields increased at Goodland, where soil moisture limits growth. Changes in daily and interannual variability of temperature result in significant changes in the mean and variability of simulated wheat yields.
As greenhouse warming occurs in the next century, changes in the mass balance of Greenland and Antarctica will probably accelerate and significantly affect global sea level. Only a few general circulation models have focused on this problem. Two runs of the Global Environmental and Ecological Simulation of Interactive Systems (GENESIS) global climate model were used to predict mass balance for present and doubled atmospheric carbon dioxide (CO2). The model is well suited for ice sheet mass-balance studies because of its fine resolution, corrections for topography distortions and meltwater refreezing, and realistic precipitation and mass balances for present-day Greenland and Antarctica. Results indicate that, in a doubled-CO2 scenario, net ablation dominates on Greenland while accumulation dominates on Antarctica. Corresponding effects on sea level would be 1.1 millimeter/year due to Greenland and -1.9 mm/year due to Antarctica.
Reconstructions of Campanian climate based on geologic data describe the age as warm, with little or no high-latitude seasonal sea ice. High sea levels caused extensive epicontinental and shallow shelf seas. Very low thermal gradients existed in the oceans and on land. GENESIS version 2.0 and EVE (Equilibrium Vegetation Ecology) models are applied to simulate Campanian climate and vegetation. Given the low Campanian meridional thermal gradient, the resulting poleward ocean heat transport has maximum values of about 1.7 x 1015 and 2.7 x 1015 watts at 25 degrees north and south, respectively. High-latitude forests helped limit seasonal ice formation.
Atmospheric tides have an important influence on the structure and dynamics of the earth's mesosphere and thermosphere. These global oscillations transfer heat and momentum to these regions from the lower atmosphere. The NCAR thermosphere-ionosphere-mesosphere- electrodynamics general circulation model (TIME-GCM) is used to study the propagation of the migrating diurnal and semidiurnal tide for both equinox and solstice conditions. TIME-GCM simulations show that, if the diurnal tide penetrates the atomic oxygen layer near 97 kilometers, then it significantly alters the atomic oxygen distribution at low latitudes. Also discussed are variations depicted in other chemical species and the resulting impact on the structure of the upper mesosphere and lower thermosphere.
The Interdisciplinary Climate Systems section of NCAR and the Fiske Planetarium have recently installed a high-resolution video projector and Internet-connected workstation in the planetarium dome. This equipment is being used to enhance many existing educational programs and products. Presented here are initial results of the synergy between hypermedia, multimedia, and the planetarium environment. Included are a hypermedia presentation of global climate model results and live use of the World Wide Web to enhance traditional education presentations.