Climate and Global Dynamics Division
|NCAR | UCAR | NSF | ASR 98|
CGD Significant Accomplishments
| For the
first time climate change experiments have been carried out with a fully coupled climate
model that employs no flux adjustments and shows no surface climate drift. These
simulations also included interactive chemical effects that have previously been ignored
A system for forecasting aerosols has been developed by members of the CGD Climate Modeling Section (William Collins, Philip Rasch, and Brian Eaton) and the Atmospheric Chemistry Division (Boris Khattatov, Jean-Francois Lamarque, and Charles Zender). The system, the first of its kind, combines a chemical transport model and an assimilation of satellite aerosol retrievals. The model simulates the three-dimensional distribution of atmospheric aerosols. The forecast system was used to plan aircraft missions during the recent Indian Ocean Experiment (INDOEX). The CGD scientists are extending the methodology to produce global aerosol analyses (See Figures, 34 K). For more information, click here.
Recent analyses of the global carbon cycle suggest a significant role for terrestrial uptake of CO2 in the overall budget. Analyses of atmospheric CO2 have persistently suggested that this terrestrial uptake is largest in the Northern Hemisphere, and spatial analyses suggest that the U.S. may play a disproportionate role.
The VEMAP Data Group at NCAR, in collaboration with the Geophysical Statistics Project
at NCAR and Chris Daly (Oregon State University), developed the model input climate data
sets for the conterminous U.S. required for Phase 2 of the Vegetation/Ecosystem Modeling
and Analysis Project (VEMAP). These consist of (1) a historical (1895-1993) gridded
time series of monthly and generated daily climate (minimum and maximum temperature,
precipitation, solar radiation, and humidity; and (2) a companion set of transient climate
change scenarios based on coupled atmosphere-ocean general circulation model experiments.
Taken together, these data sets provide the climate variables that most directly
influence ecosystems, captured at a spatial scale of variability fine enough to contain
meaningful variation for biological and hydrological systems. These data are being used by
the U.S. National Assessment and are publicly available.
With Ronald Errico (Global Dynamics Section, GDS) and Joseph Tribbia (GDS), David Baumhefner (GDS) has demonstrated that ensemble mean forecasts improved with more accurate estimation of ensemble forecast uncertainty. The skill of the ensemble means increased with increasing model resolution, which coincides with the progressive increase in predictability error growth (PEG), lowest for T42 to highest for T106.
Using an ensemble of the Community Climate Model 3 (CCM3) integrations, Grant Branstator (GDS) has estimated that there is a 90% probability that CCM3's PNA response to El Niņo is too weak.
A new formulation for horizontal viscosity has been implemented in both the full-depth and upper ocean components, based on having different coefficients in the zonal and meridional directions. By far the largest benefit of this new viscosity is that the equatorial current system in the tropical Pacific Ocean now compares very well with observations. A manuscript documenting this improvement by William Large (Oceanography Section, OS), Gokhan Danabasoglu (OS), James McWilliams (OS/University of California, Los Angeles), Peter Gent (OS), and Frank Bryan (OS) has been submitted to the Journal of Physical Oceanography.
A manuscript entitled "What sets the mean transport through Drake Passage," by Peter Gent (OS), William Large (OS), and Frank Bryan (OS) has been submitted to the Journal of Geophysical Research. The manuscript is an analysis of twelve experiments using the CSM ocean component alone, coupled to a sea-ice model, and in fully coupled CSM mode. The conclusion is that the transport is set mostly by the zonal wind stress or meridional Ekman transport and by the strength of the thermohaline circulation off the Antarctic shelf. This conclusion is not in agreement with previous hypotheses for what governs Drake Passage transport. It is shown that the transport is definitely not set by the curl of the wind stress at the latitude of Cape Horn.
Three simulations (22K) of the 21st century have been performed using a modified version of CSM. This version used a fully interactive sulfur chemistry model, and stratospheric ozone concentrations were scaled by the projected amount of reactive stratospheric chlorine. The first simulation assumed a business-as-usual increase in carbon dioxide concentration. The second simulation assumed that emission of carbon dioxide would stabilize, such that carbon dioxide concentration would reach its peak just after 2100. The third simulation was carried out as a part of the Intergovernmental Panel on Climate Change's (IPCC) Third Assessment Report.
The NCAR Paleoclimate Group has improved the PaleoCSM (a low-resolution version of CSM) and performed multi-century, fully-coupled simulations for present-day, pre-industrial times, and the mid-Holocene (4000 BC). Annual-average, global surface temperatures are 1.3ēC cooler in the pre-industrial simulation compared to the present-day simulation with the largest cooling in the middle- and high-latitude oceans in regions of sea-ice formation. Ice areas are 10% greater in both polar regions in the pre-industrial run. Increased summer and early fall insolation at northern middle latitudes during the mid-Holocene leads to delayed sea-ice formation during the fall and a 5% decrease of sea ice annually compared to pre-industrial times.
Clara Deser and collaborators have tested aspects of the Latif-Barnett and Gu and Philander hypotheses in a series of four publications. In particular, they show evidence that the North Pacific oceanic gyre circulation responded (with a delay of 4-5 yrs) to a recent decadal--scale change in wind stress curl in a manner consistent with Sverdrup theory, confirming the first part of the Latif--Barnett hypothesis. To learn more click here.
Aiguo Dai, with Kevin Trenberth and Tom Karl (National Climatic Data Center) explored how the diurnal range of surface air temperature (DTR) is affected by clouds, soil moisture, precipitation and water vapor. The DTR has decreased worldwide during the last 4-5 decades and changes in cloud cover are often cited as one of the likely causes. To learn more click here.
Tom Wigley, at the request of the Pew Center on Global Climate produced a comprehensive review of the climate change issue entitled "The science of climate change: global and U.S. perspectives" (obtainable free through www.pewclimate.org). It considers: observed changes in climate, including the issue of temperature trend differences between the surface and the lower troposphere and the problem of detecting an anthropogenic climate change signal in the observations; future greenhouse gas and sulfur dioxide emissions scenarios and concentration projections, and their global-mean temperature and sea level consequences; changes in temperature and precipitation patterns over the United States; and changes in other climate variables and in the frequency of extreme events. For more information click here.