Evaluation and application of
SEVIRI rainfall retrievals over
West Africa
Erwin Wolters1
Bart van den Hurk1,2
Rob Roebeling1
1: Royal Netherlands Meteorological Institute
(KNMI), de Bilt, Netherlands
2: Institute for Marine and Atmospheric Research
Utrecht (IMAU), Utrecht, Netherlands
Motivation
•Precipitation of great importance to hydrological
cycle
•Precipitation observations are sparse over West
Africa
•SEVIRI precipitation algorithm
daytime only
multispectral
physically based
high spatial/temporal resolution
EGU General Assembly, 6 April 2011
CPP Precipitation Properties algorithm
SEVIRI R0.6, R1.6
=f(R0.6 μm)
CWP=f(,re)
re=f(R1.6 μm)
ΔH=f(CTT)
PRP=f(CWP,ΔH)
EGU General Assembly, 6 April 2011
Evaluation: comparison with CMORPH
•
Seasonal evolution (2005) over West Africa
•
Diurnal cycle during daytime (7:30 – 16:30)
EGU General Assembly, 6 April 2011
Seasonal cycle 2005
Rain rate
CPP-PP
CMORPH
coastline
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Latitudinal cross section
May
Jul
Sep
2005
2006
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Daytime cycle June
Semi-arid
savannah
Rain forest
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Soil moisture-precipitation interaction
•Is
rain occurrence and intensity different
over wet and dry soils?
-Focus on May (pre-monsoon) and Sep
(post-monsoon)
-No rain at 7:30 UTC to avoid nighttime
MCS remnants
-Anomalies of previous-day AMSR-E soil
moisture (thanks to Richard de Jeu, Free
University of Amsterdam)
EGU General Assembly, 6 April 2011
Methodology
SEVIRI
precipitation
class “dry”
class “wet”
Normalized soil moisture
Soil moisture anomalies
AMSR-E
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Rain rate [mm h-1]
Rain occurrence [%]
Results May and Sep 2005
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Conclusions/outlook
•CPP in good agreement with CMORPH (and TRMM)
•Applicable at various time scales (seasonal,
daytime cycle)
• Unprecedented temporal resolution
•To be extended with nighttime scheme using WV
and IR channels
EGU General Assembly, 6 April 2011
12
EGU General Assembly, 6 April 2011
CPP-PP retrieval algorithm
1) Based on Wentz and Spencer (1998)
(Parameterization developed for SSM/I)
2) Roebeling and Holleman (2009)
(Parameterization modified for SEVIRI)
CWP : Condensed Water Path [g m-2]
R
: Rain Rate [mm h-1]
H
: Thickness of precipitating column [km]
H =
(CTT
max
6.0
: Offset thickness rain column [km]
EGU General Assembly, 6 April 2011
+ dH
1.6
1  CWP  CWPt 


R=
H 
CWPt

CTT : Cloud Top Temperature [K]
dH
 CTT pix )
CPP-PP retrieval algorithm
SEVIRI
Condensed
Water Path
Cloud Top
Cloud Phase Temperature
[K]
Particle size
Thickness
liquid
column
H =
(CTT
1
R=
H
Output
 CTT pix )
6.0
+ dH
 CWP  CWPt

CWPt

re (water)
> 16 m
CWP > 150 g m-2
max
Precipitation
Algorithm
Rain Rate (RR)
[mm h-1]
EGU General Assembly, 6 April 2011
1.6


