The Contribution of the Microwave Radiometer ADMIRARI to the NASA GPMGround-Validation field experiments

Pablo Saavedra Garfias1 (pablosaa@uni-bonn.de), Alessandro Battaglia2,1 and Clemens Simmer11Meteorological Institute, University of Bonn, Germany

2Department of Physics and Astronomy, University of Leicester, UK

GPM Ground Validation Experiments

The NASA Global Precipitation Measurement(GPM) Ground Validation program (GV) is provid-ing precipitation measurements from ground-basedand airborne instruments in order to support phys-ical validation of retrieval algorithms for GPM coresatellite. The set of instrumentation comprises ofairborne microphysics probe, multi-frequency radarand radiometer observations (GPM core satellite proxy)in addition to ground-based disdrometers and raingauge network. The GPM/GV instrument suite hasbeen deployed to several locations in order to studydifferent precipitation regimes, namely Tropical rainfall,light precipitation, continental convective precipitatingclouds and winter’s solid precipitation. This posteris an overview of the participation of the radiometerADMIRARI at four GPM/GV experiments from March2010 to February 2012.

Microwave Radiometer ADMIRARIThe University of Bonn’s ADvanced MIcrowaveRAdiometro for Rain Identification ADMIRARI hasbeen taking part at the GPM/GV field experimentsas an external contribution to the NASA instrumentsuite. ADMIRARI is a multi-frequency (10.7, 21.0and 36.5 GHz) dual-polarized (H & V) microwavepassive radiometer with scanning capabilities andhas the ability to distinguish the cloud and raincomponent of the liquid water content. Besidesthe passive radiometer, ADMIRARI measures withco-located ancillary instrumetns, i.e. a 24.1 GHzmicro rain radar adn a 902 nm cloud lidar.

Typical ADMIRARI data set comprise of BrightnessTemperature (V & H), Polarizaiton Difference (V - H)and the ancillary active instruments: Reflectivity at24.1 GHz and backscattering factor at 902 nm.

Microwave Radiometer ADMIRARI with thecloud lidar (left) and a rain radar (right) attachedto the scanning pedestal.

Example of data set (22sd Aug 2011) From top to bottom: MRRreflectivity, cloud lider backscattering, radiometer’s brigthnesstemperature and polarization difference.

I.CHUVA - Alcântara, Brazil

CHUVA: Cloud processes of tHe main precipitation systems in Brazil: acontribUtion to cloudresolVing modeling and to the GPM (GlobAl Pre-cipitation Measurement).Duration/Location: March 2010/Centro do Lancamente CLA (lat: 2◦

23’ 8” S, long: -44◦ 22’ 46” W).Objectives: Tropical rain, convective precipitaion, warm rain, 3D radia-tive effects [Battaglia (2011)] (http://gpm.cptec.inpe.br).

Convective warm rain (No Melting layerpresent) on March 20th, 2010. Measure-ments at 30◦ elevation angle. The fig-ures on the left depict ADMIRARI’s timeseries and the X-band radar RHI scans.The graphics on the bottom are the TB-PD space with the data (circles) colored ac-cording to the time after the event starts.Overlapped are iso-lines from simulatedrain and cloud LWP.

II.LPVEx - Parvoo, Finland

LPVEx: Light Precipitation Verification Experiment.Duration/Location: Sept-Oct 2010-Jan 2011/Emäsalo peninsula(lat: 60◦ 12’ 13” N, long: 25◦ 37’ 30” E)Objectives: High latitude precipitation, Light rain, Melting layer, snow-fall (http://lpvex.atmos.colostate.edu/).

One of the aims of ADMIRARI inLPVEx was the study of microwave sig-nature due to melting layer during lightrain. Here a case study (20-Oct-2010) isshowed.ADMIRARI’s azimuth was towardsKUMPULA C-band dual-pol radar(KUM) while it was performing RHIscans over ADMIRARI every 6 min.From those RHI scans it is possible toextract the ADMIRARI FOV for all theradar moments e.g. Z, ZDR, φDP , ρHV .

Melting Layer’s height estimation:• ZH > 10 dBz

• σ(Zdr) > 1.5

• σ(φdp) > 3.5

• elevation angles > 0.5◦

The figure above shows the MRR reflec-tivity (top), the extracted ZH from KUM(middle), the 2DVD rainrate and attenua-tion, at the bottom the ZH from KUM and2DVD DSD comparison. Rightmost panel:an individual profile at 23:45UTC.

From the KUM extracted ADMI-RARI FOV, the following is calcu-lated:• LWC(r) = aZH(r)b

• specific attenuationαν(r)HV = cHVν ZH(r)d

HVν

with ν = {10.7, 21.0 and 36.5GHz}. Two set of parametersa, b, cHVν and dHVν were com-puted using T-matrix simulationsover 1) a widely varying DSDparameters Nw, D0, µ and 2)DSDs collected over four yearsby a Joss-Walvogel JWD dis-drometer in Järvenpää, Finland.

Rain LWP can be estimated from KUM asR_LWP =

∫lwc(r)dr for the layer be-

low the detected ML. The rain LWP ob-tained by ADMIRARI (red) and 1 KUM-theo(blue) 2 KUM-JWD (black) is depicted below:

Total optical thickness:τadmirari = τrain + τcloud + τML + τgases

The cloud component can be esti-mated as follow:

τcloud ≈ 6π νIm{εw(rlidar)}|εw(rlidar) + 2|2

C_LWP

ADMIRARI optical thickness is derived from:

τadmirari = −ln(Tmr − TBνTmr − Tcos

),

Tmr : atmospheric mean radiating temperature,Tcos : MW background cosmic radiation,TBν : ADMIRARI brightness temperatures.

The figure below shows the optical thicknesses for rain (derived fromKUMPULA), cloud and total (derived from ADMIRARI):

LWP studies during snow has been done for the Extended Opservational period, more information:[Lautaportti (2012)].

III.MC3E - Oklahoma, USA

MC3E: Midlatitude Continental Convective Clouds Experiment.Duration/Location: May-June 2011/DOE-ARM Southern GreatPlains (lat: 36◦ 36’ 5” N, long: -97◦ 28’ 52” W)Objectives: Convective cloud systems, Continental mid-latitude pre-cipitation, (http://campaign.arm.gov/mc3e/).

During MC3E several convective system havebeen observed, producing significant attenuationfor MRR and almost saturation for ADMIRARI’s21 and 36.5 GHz.

Since rain drops produce a significant polarization on ADMIRARI’s frequen-cies (as seen in figure on left) the total LWP can be separated into RAIN andCLOUD components. A Bayesian approach is utilized for retrievals of rain,cloud LWP and IWV simultaneously [Saavedra (2011)]:

Ppost(x|yO) =pf (yO|x) ppr(x)∫pf (yO|x) ppr(x) dx

,

IV.GCPEx - Ontario, Canada

GCPEx: GPM Cold-season Precipitation Experiment.Duration/Location: Jan-Feb 2012/EC CARE site (lat: 44◦ 13’ 58” N, long: -79◦ 46’ 54” W)Objectives: Dry/wet Snowfall, LWP presence during snow, frozen precipitation(http://pmm.nasa.gov/GCPEx).

ADMIRARI was measuring mainly at 30◦ elevation fol-lowed by RHI scans from 21 to 60◦ at 330◦ azimuth.Below example of snow event from 30 to 31st January:

Main synergy:• King-City C-band dual-pol radar (WKR), 35km south, every 10

(IOP) or 20 min.• The University of Cologne DPR radiometer (90, 150 H&V GHz)• The NASA D3R with RHI at 330◦ azimuth, during IOP.

Below an example from WKR on Feb. 28th

The NASA D3R RHI Ku-band for the case showed on left:

LWP retrieved according to:

fk = a0(ν) + a1(ν)TBν + a2(ν)TB2ν , with:

k ∈ {LWP, IWV }ν ∈ {21.0, 36.5GHz}

Example of retrieval for Feb. 28th: The figure below, theretrievals are shown for 30◦ elevation. Note how the MRRis not sensitive to snow, on the other hand the cloud lidar(second panel) depicts clearly the snowfall as well as thecloud base.

Total LWP time series (top) for the whole GCPEx observation period, IWV (middle) and Ambient Temperaturefor reference (bottom). Snowfall events are highlighted on green:

References

[Saavedra (2011)] Saavedra P., Battaglia A., Simmer C., 2011, Partitioning of cloud water and rain water content by ground-based observations with the Advanced Mi-crowave Radiometer for Rain Identification (ADMIRARI) in synergy with a micro rain radar. J. Geo. Research., 117,D05203,doi:10.1029/2011JD016382.

[Battaglia (2011)] Battaglia A., Saavedra P., Morales C.A., Simmer C., 2011, Understanding 3D effects in polarized observations with the ground-based ADMIRARI radiome-ter during the CHUVA campaign. J. Geo. Research., 116:D09204,doi:10.1029/2010JD015335.

[Battaglia (2009)] Battaglia A., Saavedra P., Rose T., Simmer C., 2009, Characterization of precipitating clouds by ground-based measurements with the triple-frequencypolarized microwave radiometer ADMIRARI. J. Appl. Met. Clim., 49(3), pp. 394-414.

[Battaglia (2009)] Battaglia A., Saavedra P., Rose T., Simmer C., 2009, Rain observations by a multi-frequency dual polarized radiometer. IEEE Geo. Rem. Sens. Lett., 6(2),354-358.

[Lautaportti (2012)] Lautaportti S., Moisseev D., Saavedra P., Battaglia A., Chandraseker V., 2012, Dual-polarization radar and microwave radiometer observations of winterprecipitation during LPVEx. MIC_201 Ext. Abst., ERAD 2012, Toulouse-France.

[ADMIRARI WEB] http://www2.meteo.uni-bonn.de/admirari

[List of Publications] http://www2.meteo.uni-bonn.de/admirari/admirari_publications.html

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Acknowledges

The ADMIRARI project is funded by the Deutche Forschungsgemeinschaft (DFG) under grant SI 606/17-1. Special thanks toNASA GPM/GV for funding the participation in the CHUVA campaign in 2010 and the transportation from Canada to CSU-CHILL Co. USA in 2012. To the Brazilian institutions CPTEC and CLA and all their staff in Alcantara during CHUVA.The transportation and participation to the LPVEx campaign was possible due to a grant from VAISALA. Many thanks to theFMI and University of Helsinki staff for the full support during the LPVEx in Finland.Authors thank to DOE ARM for hosting the radiometer during MC3E and all the staff at Great South Plan ARM Facility fortheir continuous support, as well the McGill University crew in MC3E for the cooperation.The successful participation at GCPEx in Canada has been only possible due to the continuous support from the EC CARE sitestaff. Finally special thanks to the staff of technicians at the University of Bonn.