The effect of chosen extraterrestrial solar spectrum on clear-sky atmospheric absorption and heating rates in the near infrared

Abstract

Abstract:The extraterrestrial solar spectrum (ESS) is an important component in near infrared (near-IR) radiative transfer calculations. However, the impact of a particular choice of the ESS in these regions has been given very little attention. A line-by-line (LBL) transfer model has been used to calculate the absorbed solar irradiance and solar heating rates in the near-IR from 2000-10000 cm -1 (1-5 µm) using different ESS. For overhead sun conditions in a mid-latitude summer atmosphere, the absorbed irradiances could differ by up to about 11 Wm −2 (8.2 %) while the tropospheric and stratospheric heating rates could differ by up to about 0.13 K day −1 (8.1 %) and 0.19 K day −1 (7.6 %). The spectral shape of the ESS also has a small but non-negligible impact on these factors in the near-IR.

Can Measurements of the Near‐Infrared Solar Spectral Irradiance be Reconciled? A New Ground‐Based Assessment Between 4,000 and 10,000 cm−1

“…This controversy has primarily manifested itself in the solar physics literature, but it is of significant importance for the understanding of atmospheric processes, as SSI is a vital input into radiative transfer schemes used in climate and weather models, and in passive remote sensing systems such as MODIS (MODerate Imaging Spectroradiometer, Platnick & Fontenla, ; Thome et al, ). For example, Menang and Shine () found that using different NIR SSI from recent observations leads to ~8% differences in atmospheric absorption and heating rates. It is therefore important to measure the SSI as accurately as possible from a number of independent sources.…”

Assessment of the Impact of Solar Spectral Irradiance on Near‐Infrared Clear‐Sky Atmospheric Absorption and Heating Rates

“…It is clear from Figure that these seven spectra differ in spectral resolutions, spectral shapes, and absolute levels. However, this work will only study on the effect of the absolute levels of the SSI, since the effects of spectral resolutions and shapes on atmospheric absorption and heating rates were found to be relatively small by Menang and Shine (). It can also be observed from Figure that the two most recent SSI (CAVIAR2 and SOLAR‐ISS solar spectra) are in quite good agreement.…”

“…In a similar study by Sun et al () using a larger number of SSI (five), significant differences were also obtained in heating rates in the ultraviolet, downward solar irradiances (from ultraviolet to near IR), and changes in latitude‐height cross sections of zonal‐mean temperature. The only investigation dedicated to near IR wavelengths is that of Menang and Shine () in which they demonstrated that using different SSI in LBL radiative transfer calculations results in up to 8% differences in clear‐sky absorption and heating rates for a MLS atmosphere. However, the work of Menang and Shine () was limited to only two observed and two modeled SSI.…”

“…The only investigation dedicated to near IR wavelengths is that of Menang and Shine () in which they demonstrated that using different SSI in LBL radiative transfer calculations results in up to 8% differences in clear‐sky absorption and heating rates for a MLS atmosphere. However, the work of Menang and Shine () was limited to only two observed and two modeled SSI.…”

“…Considering the fact that there are significant disagreements between ground‐based, aircraft‐based, and satellite‐based measured SSI in the near IR (see, for example, Elsey et al, , and associated references), it is timely and important to further assess the effect of these differences on radiative transfer calculations, particularly since several very recent publications have presented new SSI, which significantly update earlier analyses. In this study, we update and extend the work of Menang and Shine () but limit our analysis to observation‐based SSI since they are generally more reliable than modeled spectra. That is, we shall investigate the effect of the choice of SSI on atmospheric absorption and solar heating rates in the near IR using three ground‐based, one airborne, and three spaced‐based observed SSI.…”