*    ISLSCP - Near Surface Meteorology

The bulk of the near-surface meteorological products on the CD were extracted from the ECMWF operational forecast analysis archive.

The data set consists of time-series of meteorological variables at 6-hourly intervals (0000Z, 0600Z, 1200Z, 1800Z) and monthly 6-hourly averages of these and many other diagnostic and prognostic variables.

The meteorological variables that are required to force land-atmosphere models with resolved diurnal cycles were extracted from this stream: surface pressure, air temperature, dew point, and wind speed (magnitude). It was also desired to have incident shortwave and longwave radiation fluxes and precipitation rates, preferably broken into large-scale and convective components, at the same 6-hourly temporal resolution.

However, the ECMWF output did not contain precipitation rates, and their radiation flux estimates were thought to be biased due to a systematic underestimation of cloud cover by the model version used to generate these products. To fill the gap, the NASA GSFC team generated hybrid radiation products: the time-series of ECMWF estimates of surface shortwave and longwave fluxes were used to divide up the NASA LaRC satellite-based monthly radiation fluxes into 6-hourly intervals. This resulted in the synthesis of 6-hourly incident shortwave and longwave fluxes that add up to match the NASA LaRC monthly means.

A similar procedure was used at NMC by Mitchell to generate 6-hourly estimates of precipitation. Six-hourly total and convective precipitation fields from the 4DDA-based NMC Reanalysis Project (Kalnay and Jenne, 1991) were used to partition the observed monthly GPCP precipitation products into 6-hourly time series of estimated total and convective precipitation, wherein the total precipitation added up to match the GPCP monthly totals. In this procedure, a screening was applied, based on the FGGE daily rainfall data, following Liston et al. (1993), to better reproduce the observed frequency of measurable daily rainfall. All of this effort has resulted in a temporally and spatially consistent meteorological forcings data set with a 6-hourly timestep. These quantities, and some others that were held on the ECMWF record at 6- hourly resolution, were processed to provide monthly 6-hourly mean products and statistics. Of particular interest are the ECMWF- generated estimates of the surface radiation and heat fluxes.

These fields were generated from a variety of sources (see the documentation) and are not recommended as initialization or boundary condition fields for current modelers. For example, the ECMWF snow-free albedo field is based on the products of Dorman and Sellers (1989), which are thought to be less accurate than the satellite-data based products. All the ECMWF fields were converted from grid cell corner point values to values representative of the entire (ECMWF) grid cell; these were then converted to the ISLSCP 1° x 1° grid and the land/sea mask was applied. In summary, a combination of products from operational meteorological agencies (ECMWF and NMC); satellite-data based radiation estimates (NASA LaRC); and global surface rain gauge analyses (GPCP) have been used to generate time- series of the required near-surface model forcings for the period 1987-1988 at a 6-hourly time resolution. These are supported by a range of ancillary time- averaged quantities that may be useful for forcing models that run on a monthly timestep.

Documentation available on CD-rom (volume1)

This data is available on Volumes 2 to 5.