Benefits of assimilating SAPHIR observations on analysis and forecasts of tropical fields in the Met Office global model. (31st July 2018)

• Record Type: Journal Article
• Authors: Doherty, A.; Indira Rani, S.; Newman, S.; Bell, W.
• Is Part Of: Quarterly journal of the Royal Meteorological Society. Volume 144(2018)Supplement 1
• Page Start: 405
• Page End: 418
• Publication Date: 2018-07-31
• Subjects: AMSR‐2 -- assimilation -- atmospheric moisture -- Megha‐Tropiques -- microwave imaging -- microwave sounding -- NWP -- SAPHIR; Meteorology -- Periodicals; 551.5
• DOI: 10.1002/qj.3258
• Languages: English
• ISSNs: 0035-9009

Abstract

Abstract : The Sondeur Atmosphérique du Profil d'Humidité Intertropicale par Radiométrie (SAPHIR) instrument provides improved sampling of tropical atmospheric moisture vertically, horizontally and temporally. The impact of these unique characteristics is investigated through: an idealised study of retrieved humidity profiles; single‐observation experiments; assimilation experiments in a global NWP system; and an investigation into the spin‐down of precipitation in the early phase of the forecast. SAPHIR offers improved performance over similar satellite instruments, and beneficial impacts were found in all investigations. When assimilated in conjunction with observations from the Advanced Microwave Scanning Radiometer imager AMSR‐2 the impact is further improved. Retrieval studies showed the errors in retrievals from SAPHIR were lower than those obtained from MHS or ATMS at all levels above 600 hPa. Single‐observation experiments showed that, when assimilated together with AMSR‐2, AMSR‐2‐driven humidity increments were modified to give more realistic vertical structure. In assimilation experiments employing a near‐operational configuration of the Met Office global model, the assimilation of clear‐sky SAPHIR data improved the root‐mean‐square errors of a number of forecast metrics, most notably temperature at 250 hPa (improved by 2%), relative humidity at 500 hPa (2%) and wind at 500 hPa (1%) at forecast lead times of 12 and 24 h. The results of this work form a clear recommendation for future remote‐sensing missions including both SAPHIR and AMSR‐2 channel configurations. Abstract : SAPHIR is a novel development in microwave humidity sounders, offering improvements over previous instruments in temporal sampling and vertical resolution and range, as shown in this plot of tropical weighting functions of three such satellite‐borne instruments. We examine the impact of SAPHIR observations on the Met Office operational global NWP system, and note improved humidity analysis increments and improved forecasts over a range of metrics. Assimilation together with the microwave imager AMSR‐2 indicates a complementarity between the two instruments.