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On the Removal of the Effect of Horizontal Fluxes In Two‐Aircraft Measurements of Cloud Absorption
Author(s) -
Marshak Alexander,
Wiscombe Warren,
Davis Anthony,
Oreopoulos Lazaros,
Cahalan Robert
Publication year - 1999
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49712555811
Subject(s) - absorption (acoustics) , flux (metallurgy) , radiative transfer , divergence (linguistics) , computational physics , cloud computing , environmental science , radiative flux , remote sensing , meteorology , physics , optics , computer science , materials science , geology , linguistics , philosophy , metallurgy , operating system
Cloud absorption inferred from the difference between the net fluxes measured by stacked aircraft below and above clouds is strongly affected by the uncertainties due to cloud horizontal inhomogeneity. the simplest way to get rid of these uncertainties is to perform grand averages over flight legs; if flight legs are long enough, grand averaging may lead to a reliable estimate of cloud absorption. However, the amount of information on ‘true’ cloud absorption returned from such an expensive measurement program will be very limited‐often one number per flight leg. This paper contains a discussion on how to enhance the harvest of true absorption data using two related methods: (a) subtraction and (b) conditional sampling. Both methods assume that, simultaneously with broadband measurements, some narrow non‐absorbing‐band net flux measurements are also available. Both methods are related to Ackerman‐Cox type corrections, where subtracting fluxes in a transparent spectral band from those in an absorbing band partially removes the radiative effects of horizontal inhomogeneity and allows the recovery of spatially resolved cloud absorption. the output of the two methods is different: while the subtraction method provides a contiguous record of recovered cloud absorption, the conditional sampling method yields a discrete set of data points where the vertical net flux divergence reliably estimates true cloud absorption.