R.: Assimilation of IASI at the Met Office and assessment of its impact through observing system experiments

• Main Authors: F. Hilton, N. C. Atkinson
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: North Atlantic
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.541.3248; http://cimss.ssec.wisc.edu/itwg/itsc/itsc16/proceedings/2_11_Hilton.pdf

Data from the Infrared Atmospheric Sounding Interferometer (IASI) onboard MetOp has been assimilated at the Met Office in both Global and North Atlantic and European (NAE) model configurations since November 2007. It has been a considerable challenge to reduce data volumes to a manageable level within the constraints of the forecast system and this paper will summarise the processing methodology employed. Pre-operational trials of IASI assimilation in the Global model delivered a positive impact on forecasts approximately twice as large as that shown by AIRS. A series of observing system experiments confirms the relative performance of IASI and AIRS, and shows that impact from IASI is equivalent to a single AMSU-A+MHS. Analysis of a second season Global model IASI assimilation trial indicates that the measurement of impact is strongly affected by variations in performance of the control forecast. Furthermore, the impact of IASI is strongly dependent on the variables and methods chosen for verification: although improvements to the large scale fields (e.g. mean sea-level pressure and geopotential height) were also seen in the NAE configuration, no forecast impact was seen for variables such as visibility and rain-rate.