COAMPS ® Ducting Validation Wallops-2000 William Thompson and Tracy Haack Naval Research Laboratory Marine Meteorology Division Monterey, CA COAMPS ® is a registered trademark of the Naval Research Laboratory

Wallops-2000 Experiment April/May 2000 Wallops-2000 Experiment  April/May 2000  NSWCDD Microwave Propagation Measurement System II (MPMS)  NSWCDD Sealion project boat  JHU/APL Chessie Boat  NPS Flux buoy (13 km shore)  JHU/APL Helicopter  SCSC resident AN/Spy-1A radar  NASA Space and Range radar *

COAMPS Non-hydrostatic, compressible equations Physical parameterizations include surface fluxes radiation turbulence microphysics Data assimilation incremental update Diagnostic computation of refractivity and ducting layers Nested domains Wallops 2000 Reanalysis  April/May hr continuous forecasts  36, 12, 4-km resolution  71 levels w/ 20 levels below 1.5 km  Sea Surface temperature analysis preformed at grid resolution  Hourly 2D and 3D forecast fields 36 km 12 km 4 km * 4-km Grid NPS Buoy COAMPS Reanalysis Wallops-2000 Experiment April/May * NPS Buoy

Modified Refractivity (M) and Ducting Properties M = 77.6/T{ P e/T} + z/Re x 1x10 6 where T is temperature in K P is pressure in mb e is vapor pressure in mb z is elevation Re is the radius of the earth A duct exists when M decreases with elevation The strength of the duct is the difference between the relative minimum in M (M m ) and the relative maximum in M The base of the duct is the elevation below M m at which the value of M is equal to M m The thickness of the duct is the difference in elevation between M m and the base of the duct

Height (m) Modified Refractivity (M-units) M = 77.6/T{ P e/T} + z/R e x 10 6 Modified Refractivity (M) and Ducting Properties Duct Thickness M max(local) Duct Base Height M min Z M Duct Strength

Animation of Duct Properties Hourly images of forecast duct strength, duct thickness, and duct base height Shading intervals: –Duct strength: 2 M units –Duct thickness: 20 m –Duct base height: 25 m Forecast from 0000 UTC 1 May to 0000 UTC 2 May 2000

Duct Strength

Duct Thickness

Duct Base Height

Forecast Cross Section of Potential Temperature (K, contours) and Mixing Ratio (g/Kg, shaded) valid 0600 UTC 1 May 2000

Forecast Cross Section of Modified Index of Refraction Valid 0600 UTC 1 May 2000

Forecast Cross Section of Potential Temperature (K, contours) and Mixing Ratio (g/Kg, shaded) valid 2300 UTC 1 May 2000

Forecast Cross Section of Modified Index of Refraction Valid 2300 UTC 1 May 2000

Base HtThickness Strength Frequency NPS % 30km % 60km % 100km % Frequency Duct Base Duct Strength Duct Thickness Duct Property Means and Time Series At NPS Buoy

Time Series at 30 km Duct Thickness Duct Strength Duct Base Frequency

JHU APL Helicopter Profiles 1 May UTC 37.8 o N, 75.4 o W Specific HumidityModified Refractivity

OBS Ducting STATS **** Duct Frequency (%) **** Num OBSMEAN OBSSTD % 48% **** Duct Base Height (m) **** Num OBSMEAN OBSSTD **** Duct Strength (M-units) **** Num OBSMEAN OBSSTD **** Duct Thickness (m) **** Num OBSMEAN OBSSTD MODEL Ducting STATS **** Duct Frequency (%) **** Num CMPMEAN CMPSTD **** Duct Base Height (m) **** Num CMPMEAN CMPSTD **** Duct Strength (M-units) **** Num CMPMEAN CMPSTD **** Duct Thickness (m) **** Num CMPMEAN CMPSTD Ducting Statistics

**** Duct Frequency (%) **** Num CMPMN OBSMN CMPSTD OBSSTD BIAS RMSE **** Duct Base Height (m) **** Num CMPMN OBSMN CMPSTD OBSSTD BIAS RMSE **** Duct Strength (M-units) **** Num CMPMN OBSMN CMPSTD OBSSTD BIAS RMSE **** Duct Thickness (m) **** Num CMPMN OBSMN CMPSTD OBSSTD BIAS RMSE ******Ducting Contingency Table****** Model Ducting Obs Ducting Duct No Duct Total Duct No Duct Total Event freq : Percent correct: Mean Squ Error : Hit Rate : Miss Rate : False alrm Rate: Corct Null Rate: Discrim Score: *both obs and model have duct within depth of obs profile Observed vs Model Ducting Statistics*

Meteorology Validation At NPS Buoy Solid – obs Dashed - model

Conclusions Forecast ducting properties over the week of the experiment varied substantially. Duct location and strength were strongly dependent on the vertical gradient in mixing ratio The onset of ducting in the morning is often missed due to excess moisture above the surface - frequently observed during southerly flow conditions Transitions in ducting are missed or incorrectly timed

Conclusions (continued ) Verification of ducting against the helicopter was hampered by limited sampling times Mean duct properties were in fair agreement but the standard deviations were in poor agreement for duct base height and duct thickness The overall percent correct in duct occurrence was 57% with a false alarm rate of 16% and a correct null rate of 84% Verification of the model at the location of the NPS buoy showed a slight cold bias and relatively good agreement in terms of relative humidity, wind speed and direction, and pressure

Extra Slides

Why is microwave refractivity sensitive to water vapor distribution?* Ducts are frequently associated with large vertical gradient in water vapor In dry air, microwave refractivity is only influenced by atmospheric density At microwave frequencies, the water dipole reorients itself rapidly enough to follow and therefore modify the electromagnetic field At higher frequencies, e. g. visible light, this does not occur Thus, the refractive index of a moist atmosphere is larger for microwaves than for shorter wavelengths * from Haack and Burk (2001)