Refractivity During IHOP_2002

1. 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. c d(Ф – Фo) —— ———— 4πf dr Refractive index: n – no = Radar Measurements of Refractive Index Target phase—phase measured at fixed ground targets 4πf —— r n c Target phase: Ф(r) = 2πf ttravel(r) =

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 • Refractivity field—Calculate differences in phase between current time and calibration file.

6. N = Refractivity near the surface • N = (n – 1) 106 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 • Refractivity scan every 5 min • 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. Refractive Index and Meteorology N = Refractivity N = (n – 1) 106 where n is the index of refraction N = 77.6 P / T + 373000 e / T2 Density termmoisture term During warm season, N varies most strongly with water vapor.

12. warm/dry cool/moist