Dr. Jun Wang

RAMS-Assimilation and Radiation Online Modeling of Aerosols (AROMA)

Central American Biomass Burning - Smoke Transport And Radiation Study (CABB- STARTS)

Nesting RAMS-AROMA with GEOS-Chem

References:

1. Motivation

Although satellite remote sensing data sets are widely used to map the geographical distribution of aerosols at high spatial and temporal resolutions and to explore the effects of atmospheric aerosols on the earth’s radiation budget, numerical models are the preferred tool for studying the role of tropospheric aerosols in modulating several important atmospheric processes such as surface energetics and atmospheric heating rates. Currently, satellite derived aerosol information is not commonly used in numerical models, especially regional models. 

Following  our previous study on assimilating satellite derived aerosol optical thickness to model the Saharan dust transport and radiative effects over the oceans [Wang et al., 2004], We continue our efforts in using geostationary satellite derived fire and smoke emission products into the mesoscale model to investigate the smoke transport on regional air quality and regional climate [Wang et al., 2005].

We select the Central America as our study region.  During every Spring season, large amount of smoke from biomass-burning fires in this region is transported to the southeastern United States, degrading the air quality, visibility, and affecting the regional environment and climate.  The smoke events in 1998 is the largest one in last decade.  As reported by CNN on May 13, 1998, "AUSTIN, Texas (AP) -- Smoke and air pollution from fires in Mexico, Honduras and Guatemala is drifting across much of the U.S. Southeast, prompting Texas officials to issue a health warning to residents throughout much of south Texas. The Texas warning was the first related to fire pollutants in the state in nearly 30 years.  …”.  In addition air quality effect, these smoke aerosols also affect the surface and air temperature through their scattering and absorbing of sunlight.  Recently, it was also found that these smoke aerosols alter the cloud properties and might intrigue the lighting over the Texas area [Lyons et al., 1998, Science; Murray et al., 2000, GRL]. The relatively high density of observation sites through the IMPROVE, EPA AIRS, and DOE ARM networks in the Southeastern U.S. provides us a golden opportunity to test the utility of satellite-based aerosol products for the modeling of smoke transport and smoke radiative effects on climate.  This is the exact goal of Central American Biomass Burning - Smoke Transport And Radiation Study (CABB- STARTS) project that was originally started as part of my Ph.D. work funded by the NASA Earth System Science Graduate Fellowship Program, and now is supported by the NOAA Global Change and Climate Postdoctoral Fellowship Program under the administration of  UCAR visiting scientist program.

2. Introduction to RAMS-AROMA

RAMS-AROMA is built upon the CSU RAMS model, but has newly developed capabilities of Assimilation and Radiation Online Modeling of Aerosols. The AROMA module is developed by Wang et al [2004], and Wang et al [2005].  In addition to all capabilities that RAMS has, RAMS-AROMA has several new features.  In RAMS-AROMA, we have replaced the original RTM in RAMS with a δ-four stream (δ-4S) RTM  in which aerosol radiative effects can be explicitly considered. RAMS-AROMA also includes an aerosol transport model in which aerosol advection (using the tracer advection module in RAMS), dry and wet deposition are all considered.  Aerosol source functions in RAMS-AROMA are specified by assimilating the satellite-based AOT and emissions.  An aerosol optical model (including optical properties of dust and smoke) and cloud optical properties are tabulated in the RAMS-AROMA as well, so that aerosol mass is converted into the AOT, which in turn is used by δ-4S RTM to include the aerosol radiative impact during the radiative transfer calculation.  Because all the new features and newly developed models are built upon the RAMS, the coupling among the aerosol transport, aerosol radiation, and meteorology are achieved simultaneously at each time step and each model grid. These unique feathers allow us to simulate the aerosol distribution with high spatiotemporal resolution, and examine the aerosol radiative feedbacks on the surface energy budget, temperature profile, as well as other boundary layer processes such as evolution of boundary layer height .

Although RAMS-AROMA has been applied successfully in several case studies [Wang et al., 2004, 2005], it, just like other models, has various limitations.  The further development is ongoing, including nesting this regional model with the Harvard's GEOS-CHEM model to improve aerosol chemistry component in RAMS-AROMA.

3. Results Highlights

see details in Wang, et al,  J. Geophys. Res., 2006. (pdf file).