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1. Are the CFSR data from the CISL RDA identical to the data available from NCDC/NOMADS?
No. As of this writing (July 2011), the following differences exist:
• "00" files: At NCEP's request, we do not distribute any "00" files. These are not true analyses (they are output from the first model timestep ~3 minutes after initialization) and should not be used that way.
• ipvhnl, ipvlnl files: NCEP inadvertently included analyses of surface temperatures in these files. These grids have very large and unrealistic values for the temperatures and should not be used. They have been removed from the CISL RDA files.
• ocnh01, ocnh02, ocnh03, ocnh04 files: NCEP labeled all of the levels for the 'Geometric depth below sea surface' grids as the '0C' isotherm level, but they should be the 2.5C, 5.0C, 10.0C, 15.0C, 20.0C, 25.0C, and 28.0C levels. This problem has been fixed in the CISL RDA files.
• ocnf01, ocnf02, ocnf03 files: NCEP labeled all of the levels for the 'Geometric depth below sea surface' grids as the '0C' isotherm level, but they should be the 2.5C, 5.0C, 10.0C, 15.0C, 20.0C, 25.0C, and 28.0C levels. This problem has been fixed in the CISL RDA files.


2. I am having trouble using subsets of the surface data in WRF. Specifically, ungrib.exe complains about the soil layers. How can I get the subsets to work with WRF?
In a GRIB2 message, the value of a vertical level is packed using a combination of a scale factor and a scaled value, and the GRIB2 standard specifies that the units must be meters. For CFSR, NCEP always uses "2" as the scale factor so that they can pack a scaled value that is in units of centimeters. Our subsetting code uses the minimum necessary scaled value and then sets the scale factor accordingly. So a scale factor/scaled value of 2/200 from NCEP and 0/2 in our subsets both resolve to a level value of 2 meters. However, ungrib.exe is coded to look just at the scaled value for the level and it ignores the scale factor. Until the WRF group fixes this problem, you will need to use a modified version of Vtable.CFSR:

GRIB1| Level| From |  To  | metgrid  | metgrid | metgrid                                 |GRIB2|GRIB2|GRIB2|GRIB2
Param| Type |Level1|Level2| Name     | Units   | Description                             |Discp|Catgy|Param|Level
-----+------+------+------+----------+---------+-----------------------------------------+-----------------------
  11 | 100  |   *  |      | TT       | K       | Temperature                             |  0  |  0  |  0  | 100 
  33 | 100  |   *  |      | UU       | m s-1   | U                                       |  0  |  2  |  2  | 100 
  34 | 100  |   *  |      | VV       | m s-1   | V                                       |  0  |  2  |  3  | 100 
  52 | 100  |   *  |      | RH       | %       | Relative Humidity                       |  0  |  1  |  1  | 100 
   7 | 100  |   *  |      | HGT      | m       | Height                                  |  0  |  3  |  5  | 100 
  11 | 105  |   2  |      | TT       | K       | Temperature       at 2 m                |  0  |  0  |  0  | 103 
  51 | 105  |   2  |      | SPECHUMD | kg kg-1 |                                         |  0  |  1  |  0  | 103 
     | 105  |   2  |      | RH       | %       | Relative Humidity at 2 m                |  0  |  1  |  1  | 103 
  33 | 105  |  10  |      | UU       | m s-1   | U                 at 10 m               |  0  |  2  |  2  | 103 
  34 | 105  |  10  |      | VV       | m s-1   | V                 at 10 m               |  0  |  2  |  3  | 103 
   1 |   1  |   0  |      | PSFC     | Pa      | Surface Pressure                        |  0  |  3  |  0  |   1 
   2 | 102  |   0  |      | PMSL     | Pa      | Sea-level Pressure                      |  0  |  3  |  1  | 101 
 144 | 112  |   0  |   1  | SM000010 | fraction| Soil Moist 0-10 cm below grn layer (Up) |  2  |  0  | 192 | 106 
 144 | 112  |   1  |   4  | SM010040 | fraction| Soil Moist 10-40 cm below grn layer     |  2  |  0  | 192 | 106 
 144 | 112  |   4  |   1  | SM040100 | fraction| Soil Moist 40-100 cm below grn layer    |  2  |  0  | 192 | 106 
 144 | 112  |   1  |   2  | SM100200 | fraction| Soil Moist 100-200 cm below gr layer    |  2  |  0  | 192 | 106 
  11 | 112  |   0  |   1  | ST000010 | K       | T 0-10 cm below ground layer (Upper)    |  0  |  0  |  0  | 106 
  11 | 112  |   1  |   4  | ST010040 | K       | T 10-40 cm below ground layer (Upper)   |  0  |  0  |  0  | 106 
  11 | 112  |   4  |   1  | ST040100 | K       | T 40-100 cm below ground layer (Upper)  |  0  |  0  |  0  | 106 
  11 | 112  |   1  |   2  | ST100200 | K       | T 100-200 cm below ground layer (Bottom)|  0  |  0  |  0  | 106 
  91 |   1  |   0  |      | SEAICE   | proprtn | Ice flag                                | 10  |  2  |  0  |   1 
  81 |   1  |   0  |      | LANDSEA  | proprtn | Land/Sea flag (1=land, 0 or 2=sea)      |  2  |  0  |  0  |   1 
   7 |   1  |   0  |      | SOILHGT  | m       | Terrain field of source analysis        |  0  |  3  |  5  |   1 
  11 |   1  |   0  |      | SKINTEMP | K       | Skin temperature (can use for SST also) |  0  |  0  |  0  |   1 
  65 |   1  |   0  |      | SNOW     | kg m-2  | Water equivalent snow depth             |  0  |  1  | 13  |   1 
-----+------+------+------+----------+---------+-----------------------------------------+-----------------------

Please note that this modified table only applies to subsets of data that you receive from us. If you are using CFSR data from whole file downloads, you will need to use the unmodified version of Vtable.CFSR.


3. What are the different products and what do they mean?
The following products are available in the 6-hourly CFSR dataset:
• Analysis: This is an instantaneous analysis of the observations of a parameter at a given initialization (reference) time.
• n-hour Forecast: This is an instantaneous forecast of a parameter at n hours after the initialization (reference) time.
• n-hour Accumulation (initial+x to initial+y): This is an n-hour accumulation for a parameter over the period starting at x hours after the initialization (reference) time and ending at y hours after the initialization time.
• n-hour Average (initial+x to initial+y): This is an n-hour average for a parameter over the period starting at x hours after the initialization (reference) time and ending at y hours after the initialization time.
• n-hour Period (initial+x to initial+y): This is an n-hour value, usually an extreme (e.g. maximum or minimum temperature) for a parameter over the period starting at x hours after the initialization (reference) time and ending at y hours after the initialization time.


4. I asked for the 1-hour Forecasts and I expected to get hourly data but I only got data at 6-hour intervals. Why?
CFSR is only initialized four times per day (00Z, 06Z, 12Z, and 18Z), so any given product is only available 4 times per day, or at 6-hour intervals. If you want hourly data, you need to combine from each of the four daily intializations 1) the analyses plus the 1- through 5-hour forecasts for parameters that are analyzed, or 2) the 1- through 6-hour forecasts for parameters that are only available as forecasts. Alternatively, you can check the CFSR Selected Hourly Timeseries Products dataset (ds093.1) to see if an hourly time series has already been assembled for the parameter/level(s) that you want.


5. Why are all values for Convective gravity wave drag zonal acceleration zeroes?
Response from NCEP: Convective gravity wave drag (CGWD) was not introduced in the CFSR forecast model that creates the background guess, but only in the forecast model that makes the 45-day sub seasonal and 9-month seasonal runs. The differences between these two models are given in the CFSv2 paper. So even though there was an output slot for the CGWD fields in the diab files for CFSR, they would all be zero.


6. Where is the surface height (orography) field in CFSR?
The orography field is stored in the grid for parameter: 'Geopotential height', level: 'Ground or water surface', and product: 'Analysis'.
NOTE:  This field does not exist in the derived products (time series and monthly means) since the field does not change with time. Instead, you will find it in the full 6-hourly dataset.


7. Where is Sea Surface Temperature (SST) in CFSR? Where is Skin Temperature?
CFSR does not label SST and skin temperature grids differently than temperature grids on other levels. Select the parameter 'Temperature' and the level 'Ground or water surface' to obtain the SST/skin temperature grids, and then use the land/sea mask to determine whether a gridpoint is over water (SST) or land (skin temperature).


8. Where is the land/sea mask in CFSR?
The land/sea mask is stored in the grid for parameter 'Land cover'. Values of '1' indicate land and '0' indicate water.
Note: There is no land/sea mask data in the hourly time series dataset (because the mask does not change with time). You will need to obtain the land/sea mask from the main 6-hourly products dataset.


9. Is relative humidity with respect to water or ice?
Relative humidity is computed as follows:
• with respect to water when temperature is > 273 deg K
• with respect to ice when temperature is < 253 deg K
• a blend of ice and water in between


10. How are the cloud levels (low, middle, high, entire atmosphere) defined?
For 45N to 45S latitude, the low cloud layer is surface to 650 mbar, the middle cloud layer is 650 mbar to 400 mbar, and the high cloud layer is 400 mbar and above. Outside of 45N to 45S, the top of the low cloud layer varies linearly to 750 mbar at the poles, and the bottom of the high cloud layer varies linearly to 500 mbar at the poles. The maximum-random vertical overlapping method used by CFSR means that cloud amounts in the low, middle, and high layers are evaluated independently, and cloud amount in the entire atmosphere layer will be close to but not necessarily exactly equal to the sum of the low, middle, and high layer cloud amounts.


11. How are the cloud fields computed?
See this document for some information on how clouds are parameterized in CFSR.


12. For directional parameters (e.g. downward heat flux, upward longwave radiation, etc.), what do the positive and negative values mean?
Positive values are in the direction of flow and negative values are in the direction opposite the flow. So for downward heat flux, a positive value means heat flow in the downward direction and a negative value means heat flow in the upward direction. For upward longwave radiation, a positive value means longwave flow in the upward direction and a negative value means longwave flow in the downward direction.


13. How can the individual one-hour averages be computed?
You can compute the one-hour average (X) ending at hour N by using the N-hour average (a) and the (N-1)-hour average (b) as follows:
X = N*a - (N-1)*b

So if you want the 1-hour Average for the period initial+3 to initial+4 (X), you would use the 4-hour Average (initial+0 to initial+4) as (a) and the 3-hour Average (initial+0 to initial+3) as (b) as follows:
X = 4*a - 3*b
.


14. How can the individual one-hour accumulations be computed?
You can compute the one-hour accumulation (X) ending at hour N by using the N-hour accumulation (a) and the (N-1)-hour accumulation (b) as follows:
X = a - b

So if you want the 1-hour Accumulation for the period initial+3 to initial+4 (X), you would use the 4-hour Accumulation (initial+0 to initial+4) as (a) and the 3-hour Accumulation (initial+0 to initial+3) as (b).


15. Why do I get negative values when I compute one-hour values?
NCEP has provided this response: "Assumption of round-off error is a possible cause contributing to the negative values (in the model, timing weight is in seconds during accumulation and radiation is called every hour). There are other issues that may also cause the values going under: such as the model timing synchronization mechanics involving the start/end process of time-average accumulators, the sequence of executing model radiation, clouds, other physics, and model dynamics processes, as well as writing out model output results. If one is sure that there is no error in the formulations being used, consider putting a zero floor value in the application."


16. What are the latitudes of the gridpoints on the 0.3-degree Gaussian grid?
89.7610, 89.4514, 89.1399, 88.8281, 88.5161, 88.2040, 87.8919, 87.5797, 87.2675, 86.9554, 86.6432, 86.3310, 86.0188, 85.7066, 85.3944, 85.0821, 84.7699, 84.4577, 84.1455, 83.8333, 83.5211, 83.2088, 82.8966, 82.5844, 82.2722, 81.9600, 81.6477, 81.3355, 81.0233, 80.7111, 80.3988, 80.0866, 79.7744, 79.4622, 79.1499, 78.8377, 78.5255, 78.2133, 77.9010, 77.5888, 77.2766, 76.9643, 76.6521, 76.3399, 76.0277, 75.7154, 75.4032, 75.0910, 74.7788, 74.4665, 74.1543, 73.8421, 73.5298, 73.2176, 72.9054, 72.5932, 72.2809, 71.9687, 71.6565, 71.3443, 71.0320, 70.7198, 70.4076, 70.0953, 69.7831, 69.4709, 69.1587, 68.8464, 68.5342, 68.2220, 67.9097, 67.5975, 67.2853, 66.9731, 66.6608, 66.3486, 66.0364, 65.7242, 65.4119, 65.0997, 64.7875, 64.4752, 64.1630, 63.8508, 63.5386, 63.2263, 62.9141, 62.6019, 62.2896, 61.9774, 61.6652, 61.3530, 61.0407, 60.7285, 60.4163, 60.1040, 59.7918, 59.4796, 59.1674, 58.8551, 58.5429, 58.2307, 57.9184, 57.6062, 57.2940, 56.9818, 56.6695, 56.3573, 56.0451, 55.7328, 55.4206, 55.1084, 54.7962, 54.4839, 54.1717, 53.8595, 53.5472, 53.2350, 52.9228, 52.6106, 52.2983, 51.9861, 51.6739, 51.3616, 51.0494, 50.7372, 50.4250, 50.1127, 49.8005, 49.4883, 49.1760, 48.8638, 48.5516, 48.2394, 47.9271, 47.6149, 47.3027, 46.9904, 46.6782, 46.3660, 46.0538, 45.7415, 45.4293, 45.1171, 44.8048, 44.4926, 44.1804, 43.8681, 43.5559, 43.2437, 42.9315, 42.6192, 42.3070, 41.9948, 41.6825, 41.3703, 41.0581, 40.7459, 40.4336, 40.1214, 39.8092, 39.4969, 39.1847, 38.8725, 38.5603, 38.2480, 37.9358, 37.6236, 37.3113, 36.9991, 36.6869, 36.3747, 36.0624, 35.7502, 35.4380, 35.1257, 34.8135, 34.5013, 34.1891, 33.8768, 33.5646, 33.2524, 32.9401, 32.6279, 32.3157, 32.0035, 31.6912, 31.3790, 31.0668, 30.7545, 30.4423, 30.1301, 29.8179, 29.5056, 29.1934, 28.8812, 28.5689, 28.2567, 27.9445, 27.6323, 27.3200, 27.0078, 26.6956, 26.3833, 26.0711, 25.7589, 25.4467, 25.1344, 24.8222, 24.5100, 24.1977, 23.8855, 23.5733, 23.2610, 22.9488, 22.6366, 22.3244, 22.0121, 21.6999, 21.3877, 21.0754, 20.7632, 20.4510, 20.1388, 19.8265, 19.5143, 19.2021, 18.8898, 18.5776, 18.2654, 17.9532, 17.6409, 17.3287, 17.0165, 16.7042, 16.3920, 16.0798, 15.7676, 15.4553, 15.1431, 14.8309, 14.5186, 14.2064, 13.8942, 13.5820, 13.2697, 12.9575, 12.6453, 12.3330, 12.0208, 11.7086, 11.3964, 11.0841, 10.7719, 10.4597, 10.1474, 9.8352, 9.5230, 9.2108, 8.8985, 8.5863, 8.2741, 7.9618, 7.6496, 7.3374, 7.0251, 6.7129, 6.4007, 6.0885, 5.7762, 5.4640, 5.1518, 4.8395, 4.5273, 4.2151, 3.9029, 3.5906, 3.2784, 2.9662, 2.6539, 2.3417, 2.0295, 1.7173, 1.4050, 1.0928, 0.7806, 0.4683, 0.1561, -0.1561, -0.4683, -0.7806, -1.0928, -1.4050, -1.7173, -2.0295, -2.3417, -2.6539, -2.9662, -3.2784, -3.5906, -3.9029, -4.2151, -4.5273, -4.8395, -5.1518, -5.4640, -5.7762, -6.0885, -6.4007, -6.7129, -7.0251, -7.3374, -7.6496, -7.9618, -8.2741, -8.5863, -8.8985, -9.2108, -9.5230, -9.8352, -10.1474, -10.4597, -10.7719, -11.0841, -11.3964, -11.7086, -12.0208, -12.3330, -12.6453, -12.9575, -13.2697, -13.5820, -13.8942, -14.2064, -14.5186, -14.8309, -15.1431, -15.4553, -15.7676, -16.0798, -16.3920, -16.7042, -17.0165, -17.3287, -17.6409, -17.9532, -18.2654, -18.5776, -18.8898, -19.2021, -19.5143, -19.8265, -20.1388, -20.4510, -20.7632, -21.0754, -21.3877, -21.6999, -22.0121, -22.3244, -22.6366, -22.9488, -23.2610, -23.5733, -23.8855, -24.1977, -24.5100, -24.8222, -25.1344, -25.4467, -25.7589, -26.0711, -26.3833, -26.6956, -27.0078, -27.3200, -27.6323, -27.9445, -28.2567, -28.5689, -28.8812, -29.1934, -29.5056, -29.8179, -30.1301, -30.4423, -30.7545, -31.0668, -31.3790, -31.6912, -32.0035, -32.3157, -32.6279, -32.9401, -33.2524, -33.5646, -33.8768, -34.1891, -34.5013, -34.8135, -35.1257, -35.4380, -35.7502, -36.0624, -36.3747, -36.6869, -36.9991, -37.3113, -37.6236, -37.9358, -38.2480, -38.5603, -38.8725, -39.1847, -39.4969, -39.8092, -40.1214, -40.4336, -40.7459, -41.0581, -41.3703, -41.6825, -41.9948, -42.3070, -42.6192, -42.9315, -43.2437, -43.5559, -43.8681, -44.1804, -44.4926, -44.8048, -45.1171, -45.4293, -45.7415, -46.0538, -46.3660, -46.6782, -46.9904, -47.3027, -47.6149, -47.9271, -48.2394, -48.5516, -48.8638, -49.1760, -49.4883, -49.8005, -50.1127, -50.4250, -50.7372, -51.0494, -51.3616, -51.6739, -51.9861, -52.2983, -52.6106, -52.9228, -53.2350, -53.5472, -53.8595, -54.1717, -54.4839, -54.7962, -55.1084, -55.4206, -55.7328, -56.0451, -56.3573, -56.6695, -56.9818, -57.2940, -57.6062, -57.9184, -58.2307, -58.5429, -58.8551, -59.1674, -59.4796, -59.7918, -60.1040, -60.4163, -60.7285, -61.0407, -61.3530, -61.6652, -61.9774, -62.2896, -62.6019, -62.9141, -63.2263, -63.5386, -63.8508, -64.1630, -64.4752, -64.7875, -65.0997, -65.4119, -65.7242, -66.0364, -66.3486, -66.6608, -66.9731, -67.2853, -67.5975, -67.9097, -68.2220, -68.5342, -68.8464, -69.1587, -69.4709, -69.7831, -70.0953, -70.4076, -70.7198, -71.0320, -71.3443, -71.6565, -71.9687, -72.2809, -72.5932, -72.9054, -73.2176, -73.5298, -73.8421, -74.1543, -74.4665, -74.7788, -75.0910, -75.4032, -75.7154, -76.0277, -76.3399, -76.6521, -76.9643, -77.2766, -77.5888, -77.9010, -78.2133, -78.5255, -78.8377, -79.1499, -79.4622, -79.7744, -80.0866, -80.3988, -80.7111, -81.0233, -81.3355, -81.6477, -81.9600, -82.2722, -82.5844, -82.8966, -83.2088, -83.5211, -83.8333, -84.1455, -84.4577, -84.7699, -85.0821, -85.3944, -85.7066, -86.0188, -86.3310, -86.6432, -86.9554, -87.2675, -87.5797, -87.8919, -88.2040, -88.5161, -88.8281, -89.1399, -89.4514, -89.7610


17. What are the definitions for the different vegetation type values?
The following table provides definitions for the vegetation type values (SiB-1) found in the CFSR grids:

Value	Description
1	Broadleaf-evergreen trees (tropical forest)
2	Broadleaf-deciduous trees
3	Broadleaf and needleleaf trees (mixed forest)
4	Needleaf-evergreen trees
5	Needleaf-deciduous trees (larch)
6	Broadleaf trees with groundcover (savanna)
7	Groundcover only (perennial)
8	Broadleaf shrubs with perennial groundcover
9	Broadleaf shrubs with bare soil
10	Dwarf trees and shrubs with groundcover (tundra)
11	Bare soil
12	Cultivations (same as for type 7)
13	Glacial (same as for type 11)



18. What are the definitions for the different soil type values?
The following table provides definitions for the soil type values (Zobler 1986) found in the CFSR grids:

Value	Description
1	Coarse texture, loamy sand, 0.82 quartz content
2	Medium texture, silty clay loam, 0.10 quartz content
3	Fine texture, light clay, 0.25 quartz content
4	Coarse-medium texture, sandy loam, 0.60 quartz content
5	Coarse-fine texture, sandy clay, 0.52 quartz content
6	Medium-fine texture, clay loam, 0.35 quartz content
7	Coarse-medium-fine texture, sandy clay loam, 0.60 quartz content
8	Organic texture, 0.40 quartz content
9	Glacial land ice, loamy sand, 0.82 quartz content



19. What are the definitions for the different soil slope type values?
The following table provides definitions for the soil slope type values (Zobler 1986) found in the CFSR grids:

Value	Percent Slope
1	0-8
2	8-30
3	> 30
4	0-30
5	0-8; > 30
6	8-30; > 30
7	0-8; 8-30; > 30
9	Glacial land ice
blank	Water



20. Why do the WRF parameter selection presets default to the 6-hour Forecasts instead of the Analyses?
Most WRF users want to use both the pressure-level and surface data to force the model, but CFSR does not analyze many of the surface parameters (e.g. - 2m temperature, 10m winds). They are only available as forecasts. The WRF group does not recommend mixing analyses and forecasts. The next question is then "Why not the 1-hour Forecasts?". Because of the WRF's internal clock, timings of some events may occur on a "6-hour" clock (e.g. - when the sun is up, etc.), so to stay consistent with the internal clock, the WRF group recommends using the 6-hour forecasts.


21. What is "Hybrid Level 1"?
Hybrid Level 1 is a terrain-following pressure level that is near the surface of the Earth. To find the pressure (in Pa) at any gridpoint on Hybrid Level 1, you will also need to know the surface pressure at that gridpoint. The formula is:
P_hybl1 = 0.99467117 * P_sfc


22. What are the pressure values at the 65 model levels?
The Climate Forecast System uses a hybrid vertical coordinate that is defined by:
P_k = A_k + B_k*P_sfc
where P_k is the pressure at level k, and P_sfc is the surface pressure
The values of A_k and B_k (units are Pa) are given in the following table:

k	A	B
0	0.0	1.0
1	0.0	0.99467117	(This is Hybrid Level 1)
2	0.57499999	0.99862660
3	5.7410002	0.98174226
4	21.516001	0.97386760
5	55.712002	0.96482760
6	116.89900	0.95443410
7	214.01500	0.94249105
8	356.22299	0.92879730
9	552.71997	0.91315103
10	812.48901	0.89535499
11	1143.9880	0.87522358
12	1554.7889	0.85259068
13	2051.1499	0.82731885
14	2637.5530	0.79930973
15	3316.2170	0.76851469
16	4086.6140	0.73494524
17	4945.0288	0.69868290
18	5884.2061	0.65988702
19	6893.1172	0.61879963
20	7956.9082	0.57574666
21	9057.0508	0.53113484
22	10171.712	0.48544332
23	11276.348	0.43921080
24	12344.490	0.39301825
25	13348.671	0.34746850
26	14261.435	0.30316412
27	15056.342	0.26068544
28	15708.893	0.22057019
29	16197.315	0.18329623
30	16503.145	0.14926878
31	16611.604	0.11881219
32	16511.736	0.092166908
33	16197.967	0.069474578
34	15683.489	0.050646842
35	14993.074	0.035441618
36	14154.316	0.023555880
37	13197.065	0.014637120
38	12152.937	0.082940198
39	11054.853	0.041067102
40	9936.6143	0.016359100
41	8832.5371	0.0043106001
42	7777.1499	0.00036969999
43	6804.8740	0.0
44	5937.0498	0.0
45	5167.1460	0.0
46	4485.4932	0.0
47	3883.0520	0.0
48	3351.4600	0.0
49	2883.0381	0.0
50	2470.7881	0.0
51	2108.3660	0.0
52	1790.0510	0.0
53	1510.7111	0.0
54	1265.7520	0.0
55	1051.0800	0.0
56	863.05798	0.0
57	698.45697	0.0
58	554.42401	0.0
59	428.43399	0.0
60	318.26599	0.0
61	221.95799	0.0
62	137.78999	0.0
63	64.247002	0.0
64	0.0	0.0



23. Do the individual data points represent some kind of gridcell average?
CFSR data are gridpoint data, not grid cell data. The values at each point represent the variable at that gridpoint. They are not averages over some larger cell.


24. What is the horizontal datum for the CFSR data?
The Climate Forecast System model assumes that the Earth is a perfect spheroid with a radius of 6371.2 km.


25. Why, when I made a subset request for just the v-component of the wind, did I only get the u-component?
The GRIB2 format allows there to be more than one grid in a GRIB2 message. NCEP has packaged its GRIB2 messages so that both grids for the u- and v-components of the wind are in the same message. Our subsetting software will give you only the GRIB2 messages that you need, but it will not split messages. So even though you ask just for the v-component, you will still get both.

If your GRIB2 decoder is not able to handle messages containing multiple grids, then you will need to find a different decoder.