Variables from the NCEP/NCAR Reanalysis The Analysis Archive In this section we will list the variables that are in the different data files from the NCEP/NCAR reanalysis. All of these fields are output each six hours. The model used for the NCEP/NCAR Reanalysis is a T62 sigma coordinate system (resolution 208 Km). There are 28 levels. The analyses are done directly in the sigma coordinate system (there is no interpolating back and forth between pressure and sigma, as in many previous methods). 1. Data volume each year from reanalysis. The following table gives an approximate volume for selected main files in the reanalysis output. File Mbytes Type of data per Year pgb.f00 2533 Analysis stack, pressure coord., 2.50 resol. grb2d 1989 Fluxes in synop sort, Gaussian grid grbsanl 4909 Sigma analyses, Gaussian grid ipvanl 1462 Analyses on theta, derived from sanl (synop sort) - 2972 Forecast data, an 8-day forecast each 5-days grib 269 Monthly means and variances ---Time sorts follow--- prs 2152 Analyses in time sort, pressure levels 2D 2606 Flux and surface fields in time sort (Gaussian, lat-lon) theta 1971 Analyses on theta in time sort 2. Data in pressure coordinates, 17 levels, 2.50 resol. (140 fields). All of these upper air and other fields are output at 2.5° resolution in a global grid (144 x 73 points). a. Data for each of 17 levels (1000-10mb), 105 fields Height, Temperature, Relative Humidity (8 levels), U wind, V wind, absolute vorticity, vertical velocity (12 levels). b. Terms at the surface Pressure at model sfc Lifted index MSL pressure elevation (constant) Precipitable water c. Data for the lowest sigma level (about 40m height): Temperature, Potential temperature, RH, U wind, V wind, Vertical velocity. d. Data in the lowest 30h Pa layer: Temperature, RH, U and V winds e. Tropopause data: Temperature, Pressure, U wind, V wind, vertical speed shear f. Maximum wind level: Temperature, Pressure, U wind, V wind. g. Humidity of layers RH in three sigma layers (overlapping layers) RH of total atmosphere 3. Time series file of the 2.50 pressure data (113 fields). This dataset (prs file) is 15% smaller in volume than the synoptic sort file (pgb.f00). This has the same data (but in time sort). However, it includes only fields on pressure surfaces. For example, it leaves out the tropopause data, the surface fields, and some other data. 4. Output on Model Levels (sigma), 174 fields. These data are output on the global Gaussian grid (192 x 94 points). The data on 28 model levels are: Temperature Relative Vorticity Sp. Humidity Divergence U wind V wind At the surface, there are 6 variables, including pressure and elevation. The total number of fields in the file of model level data are (28 x 6) plus 6. 5. Grb2d file: Two-dimensional diagnostic file ("flux fields"), 69 fields The following variables are output from the model each 6-hours. These are all on the Gaussian grid (192 x 94). These are all from the forecast model. Fields such as temperature, pressure and wind are instantaneous values at the end of the 6-hr forecast. Other data such as precipitation, radiation, etc. are averages over a six hour period. There are also specified fields (ice concentration, land-sea mask, and surface roughness). a. Surface terms: Pressure at model sfc temp at 2m Potential evap rate spec humidity 2m Latent heat flux max, min temp 2m Sensible heat flux u, v wind at 10m Temp at sfc (skin temp) b. Water terms: Convective precip Total precip rate Runoff Water equiv. of accumulated snow c. Soil terms: ground heat flux soil moisture (2 lyrs) temp of soil (3 lyrs) d. Cloud Data (19 fields): 1) Cloud cover (%) for low, middle and high clouds 2) Temperature at top of low, middle, and high clouds 3) Pressure at top and base of low, middle and high clouds 4) Nearby model level of top and base of low, middle, and high clouds 5) Cloud work function Note: Item 4 isn't really necessary, because item 3 has more precise information. e. Radiation (11 fields) up and down S Wave at sfc up and down L Wave at sfc up and down S Wave at top up L Wave at top Beam and diffuse down S Wave at sfc Near IR, beam & diffuse at sfc f. Radiation, for clouds and clear sky Cloud forcing radiation Clear sky radiation net LW top down LW sfc net LW sfc down SW sfc net LW for column up SW sfc net SW top up SW top net SW sfc up LW top net SW for column g. Miscellaneous Momentum flux, 2 components gravity wave stress, 2 components Note: It would be desirable if fields such as 10m winds and 2m temperature would also be derived from the analysis stack at time equals zero so that they would be consistent with the output of upper air analysis data (in sigma and pressure coordinates). However, as it happened, this is not the case as yet; the only version is now at the end of the 6-hour forecasts. 6. Isentropic coordinate output (89 fields). These fields are derived from model coordinate data and output on the global lat-lon (144 x 73) grid. Data are given for 11 isentropic surfaces. The variables on each of the 11 levels are given below. The number of fields are 8 x 11 plus 1 for potential temp at the model surface. Temperature Potential vorticity U and V wind Montgomery stream function Relative humidity Brunt-Vaisala frequency squared Pressure vertical velocity Note: the isentropic surfaces (K) are: 650, 550, 450, 400, 350, 330, 315, 300, 290, 280, 270. 7. The 2D file: flux and surface fields in time sort. Note that this file has more volume than grb2d. The reason is that this contains some of the other fields that might have gone into the prs file. Most of these fields are on Gaussian grid. The ones that could have been in the prs file are 2.5° lat-lon grids. 8. Data on the yearly CD-ROMs. Please see Appendix C of the March 1996 BAMS paper for a list of variables. a. A brief summary follows: Height, temp, U, V at 850, 500, 200, 100, 50 20 mb (2/day) Heights at 1000, 850, 700, 500, 300 mb (2/day) Also vertical motion, precipitable water, humidity b. Once Daily fields: Net short wave, long wave fluxes, down shortwave at sfc, precip, snow, latent, sensible fluxes, etc. c. Miscellaneous data: Monthly cross section, monthly means variances, covariances, observed OLR, display software, and documentation. 9. Output of monthly mean data, and statistics. These data are described in the Mar 1996 BAMS paper. 10. The CD-ROM with Bull. AMS (Mar 1996). This issue of BAMS had a major paper about the NCEP/NCAR Reanalysis and it has a free Reanalysis CD-ROM. The CD had monthly data for 13 years (1982-1994). It also had selections of daily data for 1993. Note that the year 1985 had been rerun, and there had been a trouble with winds near the pole on early versions of 2.5° data. The CD has the latest (and correct) version of the data. Written September 1996. The Forecast Archive for Reanalysis During reanalysis, an 8-day forecast is made each five days. The first ones each year are made on January 1, 6, 11, etc. There is output for each 12-hours during the forecast run. Data are given in pressure coordinates (2.5° resolution), and the flux fields are given (on Gaussian grid). 1. Data in pressure coordinates, 16 levels, 2.5 resolution, 128 fields. All of these upper air and other fields are output at 2.5 resolution on a global grid (144 x 73 points). a. Data for each of 16 levels (1000 - 10mb), 98 fields Height, temperature, RH (7 levels), U wind, V wind, absolute vorticity, vertical velocity (11 levels) b. Terms at the surface Pressure at model sfc lifted index MSL pressure Best (4-lyr) lifted index Precipitable water Pressure tendency c. Data in lowest 30 mb layer: Temperature, RH, U and V winds d. Tropopause data: Pressure, temperature, U wind, V wind, vertical speed shear e. Maximum wind level: Pressure, temperature, U wind, V wind f. Humidity of layers RH of three sigma layers (overlapping layers) RH of total atmosphere Note: the 16 pressure levels are: 1000, 925, 850, 700, 500, 400, 300, 250, 200, 150, 100, 70, 50, 30, 20, 10 mb. Note that 600mb is not included here. 2. Flux fields in the forecast model output, on Gaussian Grid, 43 fields. These fields are output each 12-hours from the 8-day forecast. These are on the Gaussian grid (192 x 94). a. Surface terms (10 fields) Pressure at model sfc temp at 2m Potential evap rate spec. humidity 2m Sensible heat flux max, min temp 2m Latent heat flux U, V wind at 10m b. Water terms 1) Convective precip 2) Total precip rate 3) Runoff 4) Water equiv. of accumulated snow c. Soil terms 1) ground heat flux 2) Soil moisture content d. Cloud Data (13 fields) 1) Cloud cover (%) for low, middle, and high clouds 2) Temperature at top of low, middle, and high clouds 3) Pressure at top and base of low, middle, and high clouds 4) Cloud work function (for column) e. Radiation (7 fields) 1) Up and down, s-wave at surface 2) Up and down, long-wave at surface 3) Up, long-wave at top 4) Up, s-wave at top 5) Surface albedo f. Misc. Momentum flux, 2 components (neg of sfc stress) Gravity wave stress, 2 components