Validation of TRMM rainfall products at Gadanki

T. Narayana RaoNARL, Gadanki

K. Nakamura, HyARC, Nagoya, Japan D. Narayana Rao, NARL, Gadanki

National Atmospheric Research Laboratory (NARL), Gadanki

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T)

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15 - 18

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(a) N um ber o f ra in occurrences

(b) M ean ra in rate

(c) Accum ulated ra in

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15 - 18

09 - 12

03 - 06

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09 - 12

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O RGDiurnal variation

National Atmospheric Research Laboratory (NARL), Gadanki

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Tim e (LT)00 00

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2 :00 LT 2:11 LT 2:22 LT

dBZe

13.48 N , 79.22 E 13.53 N , 79.20 E 13.50 N , 79.18 E 13.47 N , 79.17 E 13.53 N , 79.15 E 13.50 N , 79.13 E

Comparison of vertical profile of Ze

National Atmospheric Research Laboratory (NARL), Gadanki

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C olour scale is for to ta l num ber of occurrencesM ean values are ind icated by " + "

Jan Apr Jul O ct3.5

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5.5 0 C isotherm level LAW P TR M M

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Bright band statistics

National Atmospheric Research Laboratory (NARL), Gadanki

• Significant diurnal variation of rainfall is seen in SW monsoon season, whereas in the NE monsoon season it is negligible

• TRMM reproduces the diurnal variation of precipitation seen with the ORG

• Vertical profile of Ze given by profiler agrees well with that of TRMM below the bright band. The enhancement of Ze at BB is more in the case of profiler. Though, one can expect different Ze for different radars operating at different frequencies at high Z values (or at high rain rates), the difference seems to be more than one can expect.

• The bright band height variation during the course of the annul cycle is less than 250 m

• Bright band height is ~ 500 m below the 0 C isotherm level

• Height of the bright band as seen by TRMM matches with that of profiler

Conclusions

National Atmospheric Research Laboratory (NARL), Gadanki

… Thank you

Selection of suitable cases for radar calibration24 Feb 00

R eflectiv ity factor (dBZe)

D oppler ve locity (m /s)

Spectra l w idth (m /s)

Surface observations

2468

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19 N ov 99 R eflectiv ity factor (dBZe)

D oppler ve locity (m /s)

Spectra l w idth (m /s)

Surface observations

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2 0

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Rd i s d r o

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Profiler calibration

Bright band detection with a wind profiler

The algorithm looks for a peak in vertical profiles of Z in the height range of 3.5-5.5 km

+

A Doppler velocity difference of 1.5 m/s and a spectral width change of 0.3 m/s in 900 m (± 3 range bins from the Z peak).

Several rain events are studied in detail to arrive at these thresholds.

BB detection in case studies - I

28nov99R eflectiv ity factor (dBZe)

D oppler ve locity (m /s)

Spectra l w idth (m /s)

Surface observations

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5 O ct 99Reflectiv ity factor (dBZe)

Doppler velocity (m /s)

Spectra l w idth (m /s)

Surface observations

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BB detection in case studies - II22 - 23 June 00

R eflectiv ity factor (dBZe)

D oppler ve locity (m /s)

Spectra l w idth (m /s)

Surface observations

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28 - 29 June 00

R eflectiv ity factor (dBZe)

D oppler velocity (m /s)

Spectra l w idth (m /s)

Surface observations

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Data

• TRMM – 2A25 5 years (1998-2002)

• 1.3 GHz Wind profiler Precipitation in 3 rainy seasons

• Disdrometer 5 years

• ORG 5 years

Errors: Random & Measurement errors, Systematic biases ??

Resolution: 1° x 1° and 2° x 2° , near nadir and full FOV

For comparison : Surface rain (rainfall, rainrate, rain occurrence), diurnal variation of rainfall, vertical profiles and bright band statistics.

Location

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G adanki Tam ilnadu S . Int. Karnataka Rayalaseem a Coasta l Andhra

The comparison of rain parameters at the proposed site has its significance both technically and geographically.

Technically – Profilers operating at VHF and UHF bands and other ground based precipitation measurements.

Geographically – Gadanki is located close to the south-east coast of India, where the rainfall peaks in the northeast monsoon, in contrast to the rainfall in rest of India