Validation of estimation of precipitationbyDPR-GPM,using in situdata over the

peruviansAndesElver Villalobos1,2, Yamina S.2, Steven Chávez2

1Geophysical institute of Perú, 2National university of San Marcos2nd WRCP Summer School on Climate Model Development, 22-31 January 2018 SP, Brasil

IntroductionThe measurement of reflectivity factor (Z) by radar remote sensing is of great interest, because Rain Rate (R) is determined from Z. However, thesesestimates present uncertainty, because, the satellite using value of Z at a height near at surface, and considers the values of Z constant. The measurementsof R y Z proposed by Dual-frequency Pre- cipitation Radar (DPR) onboard the Global Precipitation Measurement (GPM), they are comparison andvalidate with in situ date fo the optical disdrometer, mira35C radar in Ka band, likewise, for validate was used the filter paper technique where it wasobtained the Drop Size Distribution (DSD).We used the linear regression method between R and Z, to find the paramters a and b of the empirical relationship R = aZb proposed by Marshalland Palmer (1948). As a result we obtained the values of a and b for the stratiform rainfall: Ku band a=0.020 and b=0.669, Ka band a=0.015 andb=0.675, filter paper technique a=0.017 and b=0.671, optical disdrometer a=0.027 and b=0.698 and mira35c radar a=0.015 and b=0.623. Likewise, theparameters a and b for the convective type are the following: mira35c radar a=0.001 and b=0.786 and Ku band a=0.033 and b=0.595.

Instrumentation and theory

(MS)(NS)

(HS)

Direccion de vuelo

(left) GPM core satellite, it scanes transversalto flight direction (Iguchi et al., 2010) (right)Disdrometer location in radiation atmosphericand microphysic laboratory (LAMAR) of Huan-cayo Observatory (Perú) .

(left) Paper filter with size ditribution of rain-drops measured in study area. (right) Cali-brated template (Rinehart, 1998), which wasused to measured the raindrops diameter ofstratiforme rainfall.

The reflectivity is measured by Ku band and Kaband of radares and it is defined

Z =∑v

D6 =

∫ Dmax

Dmin

N(D)D6dD (1)

Where, N(D) size distribution raindrops func-tion. Rain rate is defined

R =πρl6

∫ Dmax

Dmin

N(D)vt(D)D3dD (2)

Where vt(D) terminal velocity of raindrops andρl density of water

Results

Spacial distribution of rain rate for the period of rainfall (November-december 2014, january-marchand november-december 2015, january-march 2016). (left) Estimation of rain rate by Ku band ,(right) Estimation of rain rate by Ka band.

5 30050.1

5.1

10.1

15.1

a=0.020 b=0.669

Banda Ku−estratiforme

Reflectividad [mm 6/m3]

Ra

zon

de

llu

via

[m

m/h

]

Filter paper techinquea b

Stratiforme rainfall 0.017 0.671

Disdrometera b

Stratiforme rainfall 0.031 0.692Convective rainfall 0.024 0.627

GPM satellitea b

Stratiforme rainfall(PRKa) 0.015 0.675Stratiforme rainfall(PRKu) 0.020 0.669Convective rainfall(PRKu) 0.033 0.595

(left) Linear relationship between reflectivity (Z) and rain rate (R) for stratiforme rainfall and aand b parameters from data Ku band. (right) It shows a and b parameters for the study zone.The comparison of a and b parameters by paper filter technique, disdrometer and Ka-ku bandsradares, its are seemeds obtaindes of Iguchi et al. (2000) for stratiforme rainfall. While that a andb parametros its are diffrent for convective rainfall since it are more varies in time and space.

The band Ka did not detect convective precipitation. While band Ku did detect the stratiform andconvective rainfall where the 78% represents stratiform rainfall and 22% percent for convective.

ConclutionsIt concludes that the parameters a and b used by Ku and Ka radars (GPM), they are very close to the obtained by filter paper, disdrometer forstratoforme rainfall which validates rain rate estimates on surface. Instead, the convective rainfall is more variable at spacial and not alwasy covers thetotal area of the pixel (25km 2 ) and they are more variables at time and it more difficult for estimation correct.

Reference and acknowledgment1. Iguchi, T., S., Seto, R. Meneghini, N. Yoshida, J. Awaka, and T.

Kubota, 2010.Gmp/dpr level-2 algorithm theorical basis document.

2. Rinehart, R., 1998. Radar for Meteorologist,Rinehart, third edition.

Proyecto: Magnet-IGP “Fortalecimiento de la linea de investigación enfísica y microfísica de la atmósfera” (convenio N◦ 010/2017-FONDECYT)