This paper discusses the recent changes and improvements towards the second release of the HIRS outgoing longwave radiation (OLR) climate data record (CDR). The first release of this data set described in Lee et al. (2007) has been shown to agree very well with broadband OLR observations, particularly in the tropics. The primary objectives of the second release are to improve regional accuracy and regional time series continuity.

The ‘orbit nodal' maps were generated by gridding observations from ascending or descending orbits characterized by their equator crossing times respectively. The ascending/descending map is a frequently used mapping method that the NCDC archives the NESDIS operational AVHRR and HIRS OLR in this format. The first reprocessing of the HIRS OLR was designed to be compatible with the NESDIS operational framework, especially how the diurnal models would be applied. That mapping practice, nevertheless, puts limits on the OLR diurnal modeling that might affect the accuracy of the monthly mean derivation. With the opportunity to develop a system that would lead to operational production of HIRS OLR CDR, we are revising several components of the production procedures.

The mapping of OLR retrievals is now performed on the monthly-hourly basis that provides more accurate representation of OLR diurnal variations. We examined the consistency of the inter-satellite calibrations by comparing the monthly-hourly OLR differences to the previously established inter-satellite biases. A new set of climatological diurnal models was derived with the composite blended monthly-hourly mean data. The preliminary analysis of the impacts on HIRS OLR time series from these revisions will be shown and discussed.