Very high cloud detection in more than two decades of HIRS data

Kolat, U., P. Menzel, E. Olson, and R. A. Frey (2013), Very high cloud detection in more than two decades of HIRS data, J. Geophys. Res., 118, 3278-3284, doi:10.1029/2012JD018496.

This paper reports on the use of High-resolution Infrared Radiation Sounder (HIRS) measurements to infer the presence of upper tropospheric and lower stratospheric (UT/LS) clouds. UT/LS cloud detection is based on the fact that, when viewing an opaque UT/LS cloud that fills the sensor field of view, positive lapse rates above the tropopause cause a more absorbing CO2 or H2O-sensitive spectral band to measure a brightness temperature warmer than that of a less absorbing or nearly transparent infrared window spectral band. The HIRS sensor has flown on 16 polar-orbiting satellites from TIROS-N through NOAA19 and Metop-A and –B, forming the only 30 year record that includes H2O and CO2sensitive spectral bands enabling the detection of these UT/LS clouds. Comparison with collocated Cloud-Aerosol Lidar with Orthogonal Polarization data reveals that 97% of the HIRS UT/LS cloud determinations are within 2.5 km of the tropopause (defined as the coldest level in the National Centers for Environmental Prediction Global Data Assimilation System); more clouds are found above the tropopause than below. From NOAA-14 data spanning 1995 through 2005, we find indications of UT/LS clouds in 0.7% of the observations from 60N to 60S using CO2 absorption bands; however, in the region of the Inter-Tropical Convergence Zone (ITCZ), this increases to 1.7%. During El Niño years, UT/LS clouds shift eastward out of their normal location in the western Pacific region. Monthly trends from 1987 through 2011 using data from NOAA-10 onwards show decreases in UT/LS cloud detection in the region of the ITCZ from 1987 until 1996, increases until 2001, and decreases thereafter.

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Radiation Science Program (RSP)