Evaluation and improvement of the parameterization of aerosol hygroscopicity in global climate models using in-situ surface measurements
Poster PDF
Authors
Paul Zieger — Stockholm University
Maria Angeles Burgos — Stockholm University
Gloria Titos — University of Granada
Elisabeth Andrews — University of Colorado
Huisheng Bian — UMBC
Virginie Buchard — NASA - Goddard Space Flight Center
Gabriele Curci — Università degli Studi dell'Aquila
Alf Kirkevag — The Norwegian Meteorological Institute
Hitoshi Matsui — Nagoya University
Cynthia Randles — NASA - Goddard Space Flight Center
Kai Zhang — Pacific Northwest National Laboratory
Category
General topics – Aerosols
Description
Ambient aerosol particles have the ability to take up atmospheric water which directly impacts their light scattering properties. This hygroscopic growth effect of aerosol particles primarily depends on the particle’s chemical composition, its size and the ambient relative humidity (RH). It is usually described as the light scattering enhancement factor f(RH) defined as the particle lights scattering coefficient at elevated RH divided by its corresponding dry value. Knowledge on the effect of water-uptake on particle light scattering is needed for the precise radiative forcing calculations and for the evaluation of remote sensing and model results with in-situ measurements.
Within this project, we have re-analyzed and harmonized f(RH) measurements from 26 global sites representing most common aerosol types. Measurements were performed within the DOE/ARM, NOAA, and ACTRIS programs as well as part of several individual field campaigns. An identical data treatment process has been applied to all measurements and data quality has been assured by a thorough inspection of each dataset. This newly processed benchmark dataset has been used for (a) a global analysis of f(RH) and (b) for a model-measurement evaluation experiment within the AeroCom project.
Here, we will present a global picture of f(RH) while discussing the spatial distribution and site-specific features. A proxy study will be presented which explores the relationship between f(RH) and optical variables in order to look for possible proxies that could be used to estimate f(RH).
We will show a comparison between our in-situ benchmark dataset of f(RH) and output from several models participating in the AeroCom initiative. The goal of AeroCom is to document and understand the differences apparent in current global aerosol models based on model intra-comparisons and evaluations with measurement data. So far the following models are included in our study: GEOS-Chem, GEOS5-MERRAero, CAM5, GEOS5-GOCART, CAM5-Oslo, and CAM5-chem/ATRAS. Some models better capture observed measurement diversity while other models exhibit a narrow range of f(RH) regardless of aerosol type. All models do well at a site dominated by dust/biomass burning, but urban sites are particularly inconsistent likely due to greater variability in local sources. These results indicate that this approach shows potential for constraining simulations of aerosol/water interactions and improve model radiative forcing estimations.
