RAOB Wind Comparison


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RAOBS and MODIS/AVHRR winds are compared daily at 00Z and 12Z for differences in temperature, wind speed, and wind direction. MODIS/AVHRR winds within 150 km of a RAOB station are used in the comparison. The differences between pressure, temperature, wind speed, and wind direction are computed for winds that fall within the distance threshold. These differences are computed by subtracting MODIS/AVHRR winds data from data in each available pressure level of the RAOB sounding from the surface, up to, but not including, 150 mb. RMS speed differences are also computed for each data run along with pressure and speed biases. Weighted averages of these are then computed for each dataset (based on pole, satellite, and band).

NOTE: If either a pressure, temperature, wind speed, or wind direction is missing in the RAOB for a valid pressure level, data from that level is not included. All MODIS winds that are within 2 hours before and 1 hour after the RAOB time are used for the comparison. AVHRR winds are taken within 1 hour after 00Z and within 2 hours before and 1 hour after 12Z. Observations are taken at latitudes greater than 65 degrees for the NP and less than negative 65 degress for the SP.



The first set of plots shows temperature, wind direction, and wind speed vs pressure difference within 200 mb. Each line is a comparison between a MODIS/AVHRR wind and a ROAB sounding.

The second set of plots shows the pressure and speed biases for each pole and satellite. The pressure difference is calculated for each comparison where the speed difference is zero. If the speed difference is zero at more than one point, the closest pressure difference to zero is used. The average pressure difference, or pressure bias, is then obtained using only the pressure differences within 200 mb. The speed difference is calculated in the same way except at points where the pressure difference is zero. The average speed difference, or speed bias, is then obtained using all the speed differences available.



** ** ** ** ** ** **   Data is from Day 226 (Aug 2003) - Day 300   ** ** ** ** ** ** **
  Data starts on Day 229 for AVHRR