Retrieval of precipitation from Meteosat-SEVIRI geostationary satellite observations

Transcription

1 Retrieval of precipitation from Meteosat-SEVIRI geostationary satellite observations Jan Fokke Meirink, Hidde Leijnse (KNMI) Rob Roebeling (EUMETSAT)

2 Overview Introduction Algorithm description Validation Example cases Conclusions

3 Introduction KNMI developed method for retrieval of precipitation from passive VIS-IR imagers Method combines: Relation between liquid water path and rain rate in passive microwave retrievals (e.g., Wentz and Spencer, 1998) Relation between cloud particle phase / size and precipitation in passive VIS-NIR imagers (e.g., Lensky and Rosenfeld, 2006)

4 Precipitation retrieval scheme CPP-SEVIRI Cloud Phase Cloud Top Temperature [K] VIS 0.6 μm NIR 1.6 μm IR 11 μm Condensed Water Path [g m -2 ] LWP > 160 g m -2 Particle size [μm] r e (water) > 15 μm Height liquid column [m] Precipitation Algorithm MSG-SEVIRI 3x3 km 2 sub-sat 15 minutes Output Rain Rate (RR) [mm hr -1 ]

5 Rain Rate retrieval from SEVIRI (1) 1) Based on Wentz and Spencer (1998) (Parameterization developed for SSM/I) CWP= 125( 1+(HR) 2) Roebeling and Holleman (2009) (Parameterization modified for SEVIRI) Retrieval algorithm H = (CTT CTT max 6.5 pix 0.6 ) ) + ΔH Where CWP : Condensed Water Path [g m -2 ] R : Rain Rate [mm hr -1 ] H : Height of rain column [km] CTT : Cloud Top Temperature [K] ΔH : Offset height rain column [km]

6 Validation Netherlands Radar vs. SEVIRI Good correlation for precip occurence frequency Reasonable correlation for rain rate Roebeling and Holleman, JGR, 2009

7 Validation West-Africa Scatter plots of rainfall area and median rain rate for 127 TRMM-PR collocations Frequency distribution of rain rate compared with TRMM-PR and rain gauges Wolters et al., HESS, 2011

8 Validation Europe May-Aug Rain gauges Weather Radar SEVIRI Reasonable spatial correlation SEVIRI with rain gauges Weather radar spatial inconsistency: different radar types / retrieval algorithms Roebeling et al., J. Hydromet., 2012

9 Diurnal cycle precip occurence rain rate Roebeling et al., J. Hydromet., 2012

10 Solar zenith angle dependence Ratio of median and 95th percentile of CPP/radar rain rate as a function of solar zenith angle. Based on data over Belgium for two summers. Positive bias in CPP rain rates at high solar zenith angles probably related to 3D-effects on cloud optical thickness retrievals J. Beaumet, 2011

11 Example case 1 First: CTT~240 K, CTH~6 km Later: CTT~270 K, CTH~3 km CPP-SEVIRI weather radar 11 May 2013, 09:45-14:15 UTC

12 Example case 2 CTT~250 K, CTH~5 km CPP-SEVIRI weather radar 24 May 2013, 12:00-16:30 UTC

13 Conclusions Validation results prove skill in retrieving precipitation occurence and rain rate from passive VIS-NIR-IR Main advantages: High temporal resolution compared to polar orbiting microwave instruments High spatial resolution and uniform coverage compared to ground-based observations Main drawback: only available during daytime (and positive bias at high solar zenith angles) will add IR-based retrieval to fill this gap (albeit with lower quality)

14 Towards high-res climatologies SEVIRI mean rain rate (mm/hr) Rain gauge accumulated precip (mm/yr) Major cities and Veluwe forest area consistent Note: different quantities left and right! Brent Maddux, 2011

15 CTT~215 K, CTH~10 km Case 3 CPP-SEVIRI weather radar 12 April 2013, 09:45-14:15 UTC