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)

Radar Measurements of Refractive Index

Target phase: Ф(r) = 2πf ttravel(r) = 4πf—— r n c

Target phase—phase measured at fixed ground targets

Refractive index: n – no = c d(Ф – Фo) —— ———— 4πf dr

Radar Measurements of Refractive Index

For fixed targets, phase will change as n changes.

Radar Measurements of Refractive Index

Determining Refractivity Field

Calibration file—Calculate phase changes Calibration file—Calculate phase changes returned from (and between) stationary returned from (and between) stationary ground targets at a time of uniform ground targets at a time of uniform temperature, pressure, and moisture across temperature, pressure, and moisture across the fieldthe field

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

Water Vapor Intercomparison Workshop, Boulder, 2-3 October 2003

• N = Refractivity near the surface• N = (n – 1) 106 where n is the index of refractionN = 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

16 18 20 22 24

Time (UTC)

250

260

270

280

290

300

Refr

acti

vit

y

4

5

6

7

8

9

10

20

22

24

26

28

30

32

34

Mix

ing

Rati

o (

g k

g-1)

Mix

ing

Rati

o (

g k

g-1)

Tem

pera

ture

(o C

)

S-Pol Refractivity Data

24/7 operations from 1450 UTC 13 May 2002 24/7 operations from 1450 UTC 13 May 2002 through 1345 UTC 26 June 2002through 1345 UTC 26 June 2002

Refractivity scan every 5 minRefractivity 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

warm/dry cool/moist

Preliminary data on:Preliminary data on:http://www.atd.ucar.edu/rtf/projects/ihop_2002/spol/summary/N_quicklook/img_viewer.html

Intercomparisons to Come

N = Refractivity

N = (n – 1) 106

where n is the index of refraction

N = 77.6 P / T + 373000 e / T2

Density term moisture term

Refractive Index and Meteorology

During warm season, N varies most strongly with water vapor.

cool/moist

warm/dry