Validation of TRMM rainfall products at Gadanki

1
Validation of TRMM rainfall products at Gadanki

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

National Atmospheric Research Laboratory (NARL),
Gadanki
2
Diurnal variation
National Atmospheric Research Laboratory (NARL),
Gadanki
3
Comparison of vertical profile of Ze
National Atmospheric Research Laboratory (NARL),
Gadanki
4
Bright band statistics
National Atmospheric Research Laboratory (NARL),
Gadanki
5
Conclusions

• 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

National Atmospheric Research Laboratory (NARL),
Gadanki
6
Thank you
7
Selection of suitable cases for radar calibration
8
Profiler calibration
9
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.
10
BB detection in case studies - I
11
BB detection in case studies - II
12
Data

• 1.3 GHz Wind profiler
• Precipitation in 3 rainy seasons
• Disdrometer
• 5 years
• ORG
• 5 years

• TRMM 2A25
• 5 years (1998-2002)

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.
13
Location
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