Surface Energy Balance of the NCEP MRF and NCEP–NCAR Reanalysis in Antarctic Latitudes during FROST*

Abstract

The surface energy budget in Antarctic latitudes is evaluated for the medium-range numerical weather forecasts produced by the National Centers for Environmental Prediction (NCEP) and for the NCEP-National Center for Atmospheric Research reanalysis project during the winter, spring, and summer special observing periods (SOPs) of the Antarctic First Regional Observing Study of Troposphere project. A significant change in the energy balance resulted from an extensive model update beginning with the forecasts initialized on 11 January 1995 during the summer SOP. Both the forecasts and the reanalysis include significant errors in the surface energy balance over Antarctica. The errors often tend to cancel and thus produce reasonable surface temperature fields. General errors include downward longwave radiation about 30-50 W m Ϫ2 too small. Lower than observed cloudiness contributes to this error and to excessive downward shortwave radiation at the surface. The model albedo over Antarctica, about 75%, is lower than that derived from observations, about 81%. During the polar day, errors in net longwave and net shortwave radiation tend to cancel. The energy balance over Antarctica in the reanalysis is, in general, degraded from that of the forecasts.Seasonal characteristics of the surface energy balance include cooling over East Antarctica and slight warming over West Antarctica during NCEP forecasts for the winter SOP. Wintertime surface warming by downward sensible heat flux is larger than observations by 21-36 W m Ϫ2 and tends to balance the excessive longwave cooling at the surface. During the spring SOP, forecast sensible heat flux produces an excessive heating contribution by about 20 W m Ϫ2 . Latent heat flux during the Antarctic winter for the reanalysis is at least an order of magnitude larger than the very small observed values.

Antarctic temperature at orbital timescales controlled by local summer duration

“…SCAM contains the vertical radiation, cloud and surface-process physics of the NCAR Community Atmospheric Model but spans only a single lateral grid box, here made to coincide with the Dome F ice-core site. We specify a sensible heat-flux convergence of 100 W m −2 and a latent heat-flux convergence of 50 W m −2 , consistent with the annual average convergences over Antarctica found in the NCEP/NCAR reanalysis 43 (but which are uncertain 44 ). The latent and sensible heat convergences are distributed so as to generate uniform warming within the troposphere.…”

Cloud Cover over the South Pole from Visual Observations, Satellite Retrievals, and Surface-Based Infrared Radiation Measurements

“…Data collected at the South Pole are not only of climatological interest to the Antarctic community, but are also useful in evaluating the output of weather and climate forecast models as well as satellite retrievals of climate variables (e.g., Briegleb and Bromwich 1998;Hines et al 1999;Pavolonis and Key 2003;Guo et al 2003;Pavolonis et al 2004;Hines et al 2004). In addition, understanding the behavior of clouds and their properties is important for understanding Antarctic climate.…”

“…Lubin et al (1998) found that changing the specified phase and particle size for Antarctic clouds in the National Center for Atmospheric Research (NCAR) Community Climate Model Version 2 (CCM2) caused significant changes in the atmospheric circulation of the Southern Hemisphere. Other studies have revealed that current cloud parameterizations limit the success of Antarctic climate and weather simulations (Hines et al 1999(Hines et al , 2004. The problems associated with these parameterizations are due in part to the lack of adequate ground-truth data.…”

“…Hines et al (2004) estimated LNCRF ϭ 1 W m Ϫ2 for 1986-88 at the South Pole using the surface radiation dataset compiled by Dutton et al (1989). Rather than attempting to identify all clear scenes within a month, Hines et al (2004) chose the lowest values of LDF and LUF that occurred with the month (LDF min , LUF min ) and assigned those values to LDF clear and LUF clear . For LNCRF computed using the method of Hines et al (2004) we will use the symbol LNCRF*.…”

Spectral and Broadband Longwave Downwelling Radiative Fluxes, Cloud Radiative Forcing, and Fractional Cloud Cover over the South Pole

“…FCC has been identified as an important and poorly predicted parameter in forecasts of Antarctic climate (Hines et al 1999(Hines et al , 2004. It is important for closing the surface heat budget (Pavolonis and Key 2003), but recent efforts have been relatively unsuccessful at estimating the magnitude of any one component of the radiative surface heat budget, probably in large part because of poor knowledge of FCC.…”