1. Water Vapor Intercomparison Workshop, Boulder, 2-3 October 2003 Refractivity During IHOP_2002 Tammy M. Weckwerth (NCAR/ATD), Crystalyne R. Pettet (NCAR/ATD), Frédéric Fabry (McGill University), ShinJu Park (McGill University) and James W. Wilson (NCAR/ATD)

2. Radar Measurements of Refractive Index Target phase: Ф(r) = 2πf t travel (r) = 4πf —— r n c Target phase—phase measured at fixed ground targets Refractive index: n – n o = c d(Ф – Ф o ) —— ———— 4πf dr

3. Radar Measurements of Refractive Index For fixed targets, phase will change as n changes.

4. Radar Measurements of Refractive Index

5. Determining Refractivity Field Calibration file—Calculate phase changes returned from (and between) stationary ground targets at a time of uniform temperature, pressure, and moisture across the field Calibration file—Calculate phase changes returned from (and between) stationary ground targets at a time of uniform temperature, pressure, and moisture across the field Refractivity field—Calculate differences in phase between current time and calibration file. Refractivity field—Calculate differences in phase between current time and calibration file.

6. Water Vapor Intercomparison Workshop, Boulder, 2-3 October 2003 N = Refractivity near the surface N = (n – 1) 10 6 where n is the index of refraction N = f(e, T, P) N changes as air mass properties (moisture and temperature) change For conditions of T = 28ºC, p = 910 mb, q = 7 g kg -1, Δ1ºC = Δ1 N units Δ1 mb = Δ0.3 N units Δ1 g kg -1 = Δ6 N units

8. S-Pol Refractivity Data 24/7 operations from 1450 UTC 13 May 2002 through 1345 UTC 26 June 2002 24/7 operations from 1450 UTC 13 May 2002 through 1345 UTC 26 June 2002 Refractivity scan every 5 min Refractivity scan every 5 min Preliminary data on: Preliminary data on: http://www.atd.ucar.edu/rtf/projects/ihop_2002/ spol/summary/N_quicklook/img_viewer.html

9. warm/dry cool/moist Preliminary data on: http://www.atd.ucar.edu/rtf/projects/ihop_2002/spol/summary/ N_quicklook/img_viewer.html

10. Intercomparisons to Come

11. N = Refractivity N = (n – 1) 10 6 where n is the index of refraction N = 77.6 P / T + 373000 e / T 2 Density term moisture term Refractive Index and Meteorology During warm season, N varies most strongly with water vapor.

12. cool/ moist warm/ dry