Differential O2 Absorption Barometric Pressure Radar (DIAR_BAR): Improvements in Tropical Storm Forecasts Qilong Min 1, Bing Lin 2, Yongxiang Hu 2, Wei Gong 1, Steven Harrah 2, Wes Lawrence 3, Dion Fralick 2, 1 State University of New York, Albany, NY 2 NASA Langley Research Center, Hampton, VA 3 Old Dominion University, Norfolk, VA

 Spatial coverage: very limited  Costs: high  Uncertainty: ~1 mb Existing techniques: in-situ drift buoy moored buoy dropsonde No remote sensing technique is available. Sea surface pressure measurements Atmospheric pressure : the primary driving force for atmospheric dynamics and generates wind fields that transport mass, moisture and momentum.

Historical studies Active & passive O 2 A-band instruments active: high stable laser system --- difficult passive: daytime, cloud free, aerosol loading Microwave sounder 25 ~ 75GHz: multiple channels (6) absorption: LW, WV atmospheric and cloud temperature footprints, sea surface reflectivities

Oxygen is uniformly mixed in the atmosphere, and attenuates the transmitted signal – less at lower freq. and more at higher freq. The amount of attenuation is directly related to barometric pressure and altitude. f or 1/  GHz) P Rec Attenuation Calibrated P Rec w/o Attenuation Aircraft/Spacecraft-Based Q-Band (50-56GHz) Radar Measurement Concept

Pr ( ) = P T A e  2 (,  )  0 (, ,  )/(4  R 2 (  )) (1) Pr: radar received power; T: transmittance  ( )  exp (  O  L  V ) = exp (  O O  L L  V V) (2) where O = MP 0 /g, M: mixing ratio; P 0 : sea surface pressure Pr( 1 )/Pr( 2 )=C( 1 )C( 2 ) -1 exp(-2 (  O ( 1 )-  O ( 2 ))M O P O /g). (3) power ratio of two frequency channels at the O 2 -band Similar LW & WV absorption (50~56GHz) Almost the same in footprint & reflectivity P 0  C 0 ( 1, 2 ) + C 1 ( 1, 2 ) log e (P r ( 1 )P r -1 ( 2 )) (4) A very simple near-linear relationship between surface air pressure and radar power ratio of two different frequencies (or differential absorption index) is expected from the O 2 band radar data. Theoretical basis

Radar simulated results Most of the variability is due to global atmospheric profile variations: temperature, water vapor, clouds, etc.

PoC Instrument Development Agilent 8362B Network Analyzer SpaceK Labs 45GHz Up/Down Converter Quinstar 24" Cassegrain Antennas

Ground tests Radar Installed in/on Mobile Radar Lab relatively isolated radar reflector nearly spherical reflector ~300m clear range Projected Beamwidth

Varina-Enon Bridge I-295 South of Richmond, VA Approx. 150’ above James River Ground tests Measure Water NRCS Over Wide Inc. Ang. Support Satellite Design Supported by VDOT

PATAUXENT RIVER NAVAL AIR STATION Flight tests

Observed and simulated Differential absorption

LEO Satellite Instrument COTS & Lab Equip. Demo Concept Operational Design Op. Perf. Assessment Technology Readiness Level from 3 to 7 Global Measurements 15 ~ 22 km 0 – 3 km >220 km Airborne Instrument Proof-of-Concept Instrument Technology Roadmap

Sea level pressure (SLP) assimilation (WRF) “Simulated satellite SLP” using surface pressure measurements during first landing of Katrina Model configuration  Advanced Research WRF (ARW) dynamic solver  CCM3 Radiation  Thompson cloud microphysics and Kain-Fristch convective parameterization  Mellor-Yamada PBL  36 and 12 km horizontal resolution and 28 layers, 261×181 grid mesh  84 -hour simulation CaseAssimilation PatternScale Length Factor CTLNo GaArea GlLowest Pressure GcArea without lowest pressure GbA 2 degree band

Sea level pressure (SLP) assimilation (WRF) e f OBS NCEP-FNL Gl_.25 Gl_1.0 Ga_.25 Ga_1.0 Sea-Level Pressure at 00 UTC August 26, 2005

Sea level pressure (SLP) assimilation (WRF) CTLGl(.25)Ga(1.0) Ga(1.0)-CTLGl(.25)-CTL The assimilation runs symmetrically strengthen the cyclonic flow and enhances the westward and southward mean flow. Due to deepening of the hurricane vortex, the convective heating is enhanced Initial column wind vector (m/s) in the experiments

Ga Hurricane Katrina tracks Single point assimilations have large spread in track when different length scales are used All points assimilations have small spread in track and produce close track and landing position Gl Thick Black soild—best estimate Black dashed—CTL Sensitivity to scale length factor Black –1; Red—0.75; Green—0.5 and Black—0.25

Hurricane Katrina Intensity (84-hour: Gl, Ga, Gc and Gb) Without center pressure, Gc simulates comparable results as Ga, indicating the effect of pressure horizontal distribution in assimilation. Exp (36km) Distance (km) Minimum Pressure (hPa) Maximum Wind (Knot) CTL Ga71726 Gl Gb38628 Gc66927

Summary  The differential O 2 absorption pressure radar will provide the first remote sensing barometric data! The accuracy of instantaneous surface air pressure measurements could be ~4mb. (grid averages: errors  ~1mb)  Lab, ground, and flight tests of current prototype instrument indicate that it works  Next generation radar: operational capability  This effort will lead significant improvements in predictions of hurricane intensities and tracks. This differential O 2 absorption radar technique may dramatically extend the current, limited-point barometric capability over oceans with airborne and spaceborne instruments.