Outgoing Longwave Radiation (OLR): HIRS

"The new Climate Data Record (CDR) provides daily global climate data that are valuable as inputs into Radiation Budget Studies and verifying numerical models and can identify the variations in tropical clouds and rainfall that drive global weather patterns. The daily climate data of OLR can provide radiance observations at a 1.0x1.0 Degree resolution, creating aconsistent long term climate record of observations since 1979 .

Developed by NOAA and the University of Maryland, the OLR – Daily CDR data are derived from the High Resolution Infrared Radiation Sounder (HIRS) instruments on board NOAA TIROS-N series and Eumetsat MetOp polar orbiting satellites, and the legacy and present day Imager instruments on board the multinational operational geostationary satellites. This product will be extended with the new generations of operational sounding instruments on board Suomi‐NPP, JPSS, MetOp, etc., and imaging instruments on board geostationary satellites." [http://www.ncdc.noaa.gov/cdr/operationalcdrs.html#2]

"The product contains the 1-degree by 1-degree daily mean outgoing longwave radiation flux at the top of the atmosphere derived from HIRS radiance observations onboard NOAA TIROS-N series and MetOp satellites. The OLR retrieval uses multispectral regression models (Ellingson et al., 1989, Lee, 2014). The CDR processing includes HIRS radiance calibration, inter-satellite HIRS OLR calibration, normalization of geostationary-based  OLR retrieval to HIRS, and grid-based 7-day boxcar temporal integration assisted with Imager-based OLR derived from Gridsat CDR data (Lee, 2014)."

OLR (Outgoing Longwave Radiation) is a measure of the amount of energy emitted to space by earth's surface, oceans and atmosphere. As such, it is a critical component of the earth's radiation budget. In a different context, OLR values are often used as a proxy for convection in tropical and subtropical regions since cloud top temperatures (colder is higher) are an indicator of cloud height.

OLR estimates are a key component for the standard Madden-Julian Oscillation (MJO) CLIVAR diagnostics which are used to study the MJO and for climate model evaluation.