Interpretation of Mauna Loa atmospheric transmission relative to aerosols, using photometric precipitable water amouts

Abstract

Precipitable water measurements made coincident in time and space with direct broadband solar irradiance measurements are used in conjunction with an atmospheric transmission model to derive a parameter whose major dependence is on total aerosol extinction.Irradiance measurements are used to calculate an atmospheric transmission factor (ATF) that is independent of the instrument calibration and the extraterrestrial solar constant.The dependency of the ATF on precipitable water is determined using LOWTRAN5, an atmospheric transmission model with high spectral resolution.Precipitable water measurements are then used to adjust the measured ATF to correspond to an ATF value obtained for a constant precipitable water amount.The remaining variability in the adjusted ATF is due mostly to aerosol extinction.The technique is applied to a 6-year period (1978"1983) for clear-sky mornings at Mauna Loa, Hawaii (MLO). MLO ATF aerosol residuals are compared with independently measured monochromatic aerosol optical depth.Results show that the ATF aerosol residual is nearly equal to the 500 nm aerosol optical depth prior to the eruption of E1 Chichon, at which time a nonlinear time-dependent relationship between the two quantities is evident.ATF aerosol residuals reflect the spectrally integrated aerosol influence on transmission and, therefore, could indicate better than monochromatic optical depth the radiation balance perturbations due to aerosols.The 6-year precipitable water record for MLO, determined from a dual-channel sunphotometer, has a mean value of 0.3 cm. An annual cycle in precipitable water is evident, as is a 4-month 5-standard-deviation "drought"

State of the Climate in 2016

“…This analysis is also limited to clear-sky periods to remove cloud effects and to highlight the influence of aerosols or other trace gases in the atmospheric column. Past studies of changes in clear-sky AT at MLO have investigated the influences of volca- | S42 nic aerosol, aerosol transport from Asia, ozone, water vapor, and the quasi-biennial oscillation (Bodhaine et al 1981;Dutton 1992;Dutton and Bodhaine 2001;Dutton et al 1985). However, effects due to aerosols are the most prominent.…”

On the Relation Between Solar Activity and Clear-Sky Terrestrial Irradiance

“…For the analysis in this paper, the ground-based direct-beam solar irradiance data taken since 1958 at Mauna Loa Observatory (MLO, latitude 19.533 • N, longitude 155.578 • W, elevation 3 400 m) are used (Ellis and Pueschel, 1971;Dutton, Deluisi, and Austring, 1985;Dutton et al, 1994;Dutton and Bodhaine, 2001). These measurements have been obtained at local noon as well as at airmass values of 2, 3, 4, and 5 (both in the morning and in the afternoon).…”

Global Extinction: Gemini North and South GMOS Combined Photometry Relative to the Gaia Catalog, and Long-term Atmospheric Change

“…These are obtained in visible light, most sensitive at 0.6 μm. They are already well-studied, looking for episodic (and punctuated) events related to solar and seasonal cycles; and after accounting for these, there was found to be a slow trend, consistent with up to −0.15% per decade change in transparency prior to 2000 (Dutton et al 1985;Dutton & Bodhaine 2001), and possibly steepening afterward (Dutton et al 2011).…”