Monday, 11 August 2003: 8:30 AM
An evaluation of the radar refractivity retrieval during IHOP_2002
The International H2O Project (IHOP_2002) was designed to sample the three-dimensional time-varying moisture field to better understand convective processes. Numerous research and operational water vapor measuring systems and retrievals were operated in the U.S. Southern Great Plains from 13 May to 25 June 2002. This was done in combination with more traditional observations of wind and temperature. One of the new moisture retrieval algorithms, the radar refractivity retrieval was run on NCARís S-Pol Doppler radar. This technique shows great promise for both research and operational applications. The refractivity signal is derived from the difference in radar signal phase delay between two ground targets measured at a reference time exhibiting no refractivity gradients and a time of meteorological interest. This signal delay difference is due to atmospheric refractivity variations which are caused by changes in pressure, temperature and most strongly, water vapor. During IHOP a field of refractivity measurements was routinely obtained from the S-Pol radar in the Oklahoma panhandle. The nominal retrieval range was approximately 40 km but it extended 60 km toward the northwest due to the more numerous ground targets and more optimal slope of the land. This study will examine the representative horizontal scale and vertical depth of the refractivity retrievals. Comparisons between the refractivity field and fixed and mobile mesonets within refractivity range show a strong correlation between surface moisture and refractivity, as expected from theory. There is a less distinct inverse correlation between surface temperature and refractivity. This suggests that the radar refractivity field is representative of the surface-layer atmospheric refractivity distribution and will be useful for describing the near-surface water vapor field. Comparisons between the refractivity field and low-flying aircraft support these results. Numerous instruments that profile the temperature and moisture structure will be compared with the refractivity field to assess the layer over which refractivity is representative.