Date of Award

Spring 1-1-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Atmospheric & Oceanic Sciences

First Advisor

Owen B. Toon

Second Advisor

Karen H. Rosenlof

Abstract

A sectional aerosol model (CARMA) has been developed and coupled with the Community Earth System Model (CESM1). Aerosol microphysics, radiative properties and interactions with clouds are simulated. The model described here uses 20 particle size bins for each aerosol component including freshly nucleated sulfate particles, as well as mixed particles containing sulfate, primary organics, black carbon, dust and sea salt. In this thesis, CESM1/CARMA is firstly constrained by a variety of observations, and then utilized to investigate several scientific topics including aerosol layers in the upper troposphere and lower stratosphere as well as forest fire smoke in the lower troposphere.

Recent studies reveal layers of enhanced aerosol scattering in the upper troposphere and lower stratosphere over Asia (ATAL) and North America (NATAL). The observed aerosol extinction enhancement is reproduced by CESM1/CARMA. Both model and observations indicate a strong gradient of the sulfur-to-carbon ratio from Europe to the Asia on constant pressure surfaces. We found that the ATAL is mostly composed of sulfates, surface-emitted organics and secondary organics; the NATAL is mostly composed of sulfates and secondary organics. The model also suggests emission increases in Asia between 2000 and 2010 led to an increase of aerosol optical depth of the ATAL by 0.002 on average, which is consistent with observations.

The Rim Fire of 2013, the third largest area burned by fire recorded in California history, is simulated by CESM1/CARMA. Modeled aerosol mass, number, effective radius, and extinction coefficient are within variability of data obtained from multiple airborne measurements. Simulations suggest Rim Fire smoke may block 4-6% of sunlight reaching the surface, with a cooling efficiency around 120-150 W m-2 per unit aerosol optical depth. This study shows that exceptional events like the 2013 Rim Fire can be simulated by a climate model with one-degree resolution, though that resolution is still not sufficient to resolve the smoke peak near the source region.

Share

COinS