Evaluation of rainfall retrievals from SEVIRI reflectances over West Africa using TRMM-PR and CMORPH

Abstract

Abstract. This paper describes the evaluation of the KNMI Cloud Physical Properties -Precipitation Properties (CPP-PP) algorithm over West Africa. The algorithm combines condensed water path (CWP), cloud phase (CPH), cloud particle effective radius (r e ), and cloud-top temperature (CTT) retrievals from visible, near-infrared and thermal infrared observations of the Spinning Enhanced Visible and Infrared Imager (SEVIRI) onboard the Meteosat Second Generation (MSG) satellites to estimate rain occurrence frequency and rain rate. For the 2005 and 2006 monsoon seasons, it is investigated whether the CPP-PP algorithm is capable of retrieving rain occurrence frequency and rain rate over West Africa with sufficient accuracy, using Tropical Monsoon Measurement Mission Precipitation Radar (TRMM-PR) as reference. As a second goal, it is assessed whether SEVIRI is capable of monitoring the seasonal and daytime evolution of rainfall during the West African monsoon (WAM), using Climate Prediction Center Morphing Technique (CMORPH) rainfall observations. The SEVIRI-detected rainfall area agrees well with TRMM-PR, with the areal extent of rainfall by SE-VIRI being ∼10% larger than from TRMM-PR. The mean retrieved rain rate from CPP-PP is about 8% higher than from TRMM-PR. Examination of the TRMM-PR and CPP-PP cumulative frequency distributions revealed that differences between CPP-PP and TRMM-PR are generally within +/−10%. Relative to the AMMA rain gauge observations, CPP-PP shows very good agreement up to 5 mm h −1 . However, at higher rain rates (5-16 mm h −1 ) CPP-PP overestimates compared to the rain gauges. With respect to the second goal of this paper, it was shown that both the accumulated precipitation and the seasonal progression of rainfall throughout the WAM is in good agreement with CMORPH, although CPP-PP retrieves higher amounts in the coastal reCorrespondence to: E. L. A. Wolters (wolterse@knmi.nl) gion of West Africa. Using latitudinal Hovmüller diagrams, a fair correspondence between CPP-PP and CMORPH was found, which is reflected by high correlation coefficients (∼0.7) for both rain rate and rain occurrence frequency. The daytime cycle of rainfall from CPP-PP shows distinctly different patterns for three different regions in West Africa throughout the WAM, with a decrease in dynamical range of rainfall near the Inter Tropical Convergence Zone (ITCZ). The dynamical range as retrieved from CPP-PP is larger than that from CMORPH. It is suggested that this results from both the better spatio-temporal resolution of SEVIRI, as well as from thermal infrared radiances being partly used by CMORPH, which likely smoothes the daytime precipitation signal, especially in case of cold anvils from convective systems. The promising results show that the CPP-PP algorithm, taking advantage of the high spatio-temporal resolution of SEVIRI, is of added value for monitoring daytime precipitation patterns in tropical areas.

Validation of GPM IMERG V05 and V06 Precipitation Products over Iran

“…Although model simulations, for example, European Centre for Medium-Range Weather Forecasts (ECMWF; Persson 2001) and Modern-Era Retrospective Analysis for Research and Application (MERRA;Rienecker et al 2011), have solved the spatial issue of precipitation data, their accuracy is not reliable (Anagnostopoulos et al 2010). On the other hand, satellite observations provide a unique opportunity to estimate (near) real-time precipitation globally with promising accuracy (Wolters et al 2011) that would be beneficial, especially for areas like Iran, where ground-based observations are scarce (Javanmard et al 2010). Therefore, estimating precipitation from remote sensing observations has become one of the main approaches to measuring precipitation in the last decades (Tan et al 2015).…”

Uncertainties in Evapotranspiration Estimates over West Africa

“…The ensemble of ALMIP-1 models revealed that total annual ET corresponds to 77% of the total annual precipitation in West Africa and 85% in the Sahel [21]. The annual precipitation cycle is highly subject to the West African monsoon [22]. Overall, the average precipitation rates increase southwards.…”

Accuracy of satellite rainfall estimates in the Blue Nile Basin: Lowland plain versus highland mountain

“…A number of validation efforts are underway worldwide to quantify the estimation errors, such as, the efforts of the International Precipitation Working Group (IPWG) covering Australia, Northern Europe, and North and South America [ Kidd et al ., ]. Validation studies in Africa are typically concerned with large‐scale and long‐term averages and therefore do not provide estimation error information at the native resolution of the satellite rainfall products useful for hydrological applications [e.g., Hirpa et al ., ; Yin and Gruber , ; Beighley et al ., ; Dinku et al ., ; Romilly and Gebremichael , ; Wolters et al ., ; Xue et al ., ; Adjei et al ., ; Habib et al ., ; Liechti et al ., ; Thiemig et al ., ; Novella and Thiaw , ]. The main challenge is that Africa has a very sparse rain gauge network, and the vast majority of the continent has no ground‐based weather radar.…”