Refractivity in the Coastal Atmospheric Boundary Layer

Stephen Burk and Tracy HaackNaval Research Laboratory

Monterey, CA

Refractivity in the Coastal Atmospheric Boundary Layer

Hei

ght

Q

base

top

Strength (M)

Thickness (= top-base)

Modified Refractivity, M

Hei

ght

Potential Temperature &Specific Humidity

COAMPSTM 27km grid

Cook & Burk, 1992, BLM, 58, 151-159.Burk & Thompson, 1997, JAM, 36, 22-31.Haack & Burk, 2001, JAM, 40, 673-687.Burk, Haack, Rogers, & Wagner, 2003, JAM, 349-367.

INDIA

SAUDIARABIA

Wallops 2000EM PropagationField Experiment

from NSWCDD/TR-01/132

COAMPSTM Wallops Island

DTG: 10-12 Apr 2000 Triple nest: 27-9-3 km Vertical: 40 levels

10-m Winds/SLPSST/SLP

DMDZ/THETA

Hei

ght (

m)

x = 3 km

x = 27 km

April 10, 20001200 UTC

April 11, 20001200 UTC

April 12, 20001200 UTC

EDH(m)

RH(%)

T(0C)

U(m/s)

Dots = COAMPSTM forecast values

Ta

IR

Obs from Davidson, NPS

3 am LT10 Apr 2000

Norfolk*

Wallops

COAMPSTM SST and Ground Temperature

*284

297

COAMPSTM Sensible Heat Flux (W/m2);near surface streamlines

11 Apr 2000

3 am LT 3 pm LT

0

0

0

60

20

-20

400

20

60

40

20

0

0

0

0

20

-20

COAMPSTM Evaporation Duct Height (m)11 Apr 2000

3 am LT 3 pm LT

4

6 10

12

24

2

4

8

28

base

top

Strength (M)

Modified Refractivity, M

Hei

ght

hourly fields from 00 UTC 11 Apr-2300 UTC 12 Apr 2000

Animation of two 24h COAMPSTM forecasts of:40m(shaded); 50m streamlines; & dM/dz = 0 isosurface (white)

Horizontal: Evaporation Duct Height (shaded) & StreamlinesVertical: Potential Temperature (shaded & contoured)“Clouds”: Trapping Layer (DMDZ=0 isosurface)

0

1 km

North South

M Crossection

(a)

M CrossectionShaded with dM/dz

(b)

1800 UTC 12 Apr 2000 COAMPSTM

Looking toward SE across Tidewater PeninsulaRed Isosurface dM/dz = 157 M-units/km subrefractionWhite isosurface dM/dz = 0 M-units/km trapping layer

(c)

Mixing Ratio (g/kg), Shaded;Potential Temperature (K),contoured

1800 UTC 12 Apr 2000 COAMPSTM

Duct parameters from COAMPSTM

1800 UTC 12 Apr 2000Wallops Island

Duct Base Height (m) Duct Thickness (m) Duct Strength (M-units)

0

100

200

300

400

500

0

100

200

300

0

3

6

9

12

15

18

Summary

• COAMPSTM forecasts both evaporation ducts and elevated and/or surface based ducts

• To date, most modeling studies of refractivity/propagation have focused on subsidence dominated, strongly capped BL’s (e.g., CA coast in summer; Persian Gulf)

• Intensive Observation Periods of the Wallops-2000 propagation field experiment are addressed here using COAMPSTM at high resolution. Model refractivity will be inserted into propagation codes for comparison with prop measurements.

• New insights into refractivity structure in frontal regions are emerging

• Accurate forecasting of major synoptic features (e.g., frontal boundaries) can be of greater importance than extremely high model resolution in defining local refractive structure/ EM propagation conditions. Mesoscale ensembles may be very useful in this context.