Polar mesospheric cloud mass and the ice budget: 1. Quantitative interpretation of mid-UV cloud brightness observations

Abstract

We investigate the retrieval of column ice mass from mid-UV solar scattering polar mesospheric cloud (PMC) observations to help constrain estimates of the ice budget of the polar summer mesosphere. First, we show that the backscattered brightness from PMC particles is roughly proportional to the mass of the ice particles. Second, we quantify the sensitivity of the retrieved PMC column ice mass to the particle size distribution for a viewing geometry typical for a subset of Solar Backscattered UltraViolet (SBUV) satellite data taken at 70 ± 2.5°N. Considering a wide range of Gaussian size distributions using spherical particles with peak radii between 15 nm and 100 nm and widths between 10 nm and 20 nm, we find that we can constrain the inferred ice column mass to ±43% for 95% of the distributions in this range. For this scenario we also show that spheroids with axis ratios of 0.5, 2.0 and 5.0 generally decrease the sensitivity of the inferred ice column mass to the size distribution. Third, we quantify the sensitivity of the retrieved PMC column ice mass for a viewing geometry typical for a subset of Student Nitric Oxide Explorer (SNOE) satellite data. Using the same wide range of size distributions, we show that the inferred ice column mass can be constrained to ±33% for 95% of the distributions in this range. The results of this paper are used by two companion papers to investigate the polar mesospheric ice budget.