Climate Model–Simulated Diurnal Cycles in HIRS Clear-Sky Brightness Temperatures

Abstract

Clear-sky brightness temperature measurements from the High-Resolution Infrared Radiation Sounder (HIRS) are simulated with two climate models via a radiative transfer code. The models are sampled along the HIRS orbit paths to derive diurnal climatologies of simulated brightness temperature analogous to an existing climatology based on HIRS observations. Simulated and observed climatologies are compared to assess model performance and the robustness of the observed climatology.Over land, there is good agreement between simulations and observations, with particularly high consistency for the tropospheric temperature channels. Diurnal cycles in the middle-and upper-tropospheric water vapor channels are weak in both simulations and observations, but the simulated diurnal brightness temperature ranges are smaller than are observed with different phase and there are also intermodel differences. Over sea, the absence of diurnal variability in the models' sea surface temperatures causes an underestimate of the small diurnal cycles measured in the troposphere.The simulated and observed climatologies imply similar diurnal sampling biases in the HIRS record for the tropospheric temperature channels, but for the upper-tropospheric water vapor channel, differences in the contributions of the 24-and 12-hourly diurnal harmonics lead to differences in the implied bias. Comparison of diurnal cycles derived from HIRS-like and full model sampling suggests that the HIRS measurements are sufficient to fully constrain the diurnal behavior.Overall, the results suggest that recent climate models well represent the major processes driving the diurnal behavior of clear-sky brightness temperature in the HIRS channels. This encourages further studies of observed and simulated climate trends over the HIRS era.

HIRS channel 12 brightness temperature dataset and its correlations with major climate indices

“…In addition to spectral response function changes, HIRS instruments from different polar orbiting satellites observe a location at different times of a day, which can introduce diurnal biases. As shown in Lindfors et al (2011) and MacKenzie et al (2012), the diurnal amplitudes for T B s from channel 12 are generally within 0.5 K. Based on overlapping satellites' monthly zonal averages from the Equator to the poles, Shi and Bates (2011) quantified these combined intersatellite biases for HIRS channel 12 on TIROS-N, NOAA satellite series, and METOP-A. The combined intersatellite biases, except those between NOAA-14 and NOAA-15, were found to be within ±1.8 K. The biases between NOAA-14 and NOAA-15 can exceed 8 K due to the spectral response function shift.…”

Satellite-Based Atmospheric Infrared Sounder Development and Applications

“…However, its characterization in current reanalysis data and climate models is insufficient (Allan et al 2003;Iacono et al 2003;Solomon et al 2010;MacKenzie et al 2012). More recently, hyperspectral observation data from AIRS, IASI, and CrIS are being used for analyzing UTWV (Susskind et al 2003;Liu et al 2009;Divakarla et al 2014).…”

Orbital variations and impacts on observations from SNPP, NOAA 18-20, and AQUA sun-synchronous satellites

“…Following [8,9], the diurnal cycle of BT variation was fitted with a second order Fourier series (Eq. 1).…”