Assessment of NAAPS-RA performance in Maritime Southeast Asia during CAMP2Ex
Authors: Edwards Eva-Lou , Reid Jeffrey S. , Xian Peng , Burton Sharon P. , Cook Anthony L. , Crosbie Ewan C. , Fenn Marta A. , Ferrare Richard A. , Freeman Sean W. , Hair John W. , Harper David B. , Hostetler Chris A. , Robinson Claire E. , Scarino Amy Jo , Shook Michael A. , Sokolowsky G. Alexander , van den Heever Susan C. , Winstead Edward L. , Woods Sarah , Ziemba Luke D. , Sorooshian Armin 
Published: October 2022

Abstract. Monitoring and modeling aerosol particle life cycle in Southeast Asia (SEA)
is challenged by high cloud cover, complex meteorology, and the wide range
of aerosol species, sources, and transformations found throughout the
region. Satellite observations are limited, and there are few in situ
observations of aerosol extinction profiles, aerosol properties, and
environmental conditions. Therefore, accurate aerosol model outputs are
crucial for the region. This work evaluates the Navy Aerosol Analysis and
Prediction System Reanalysis (NAAPS-RA) aerosol optical thickness (AOT) and
light extinction products using airborne aerosol and meteorological
measurements from the Cloud, Aerosol, and Monsoon Processes Philippines
Experiment (CAMP2Ex) conducted in 2019 during the SEA southwest monsoon
biomass burning season. Modeled AOTs and extinction coefficients are
compared to those retrieved with a high spectral resolution lidar (HSRL-2).
Agreement between simulated and retrieved AOT (R2= 0.78, relative
bias =-5 %, normalized root mean square error (NRMSE) = 48 %) and
aerosol extinction coefficients (R2= 0.80, 0.81, and 0.42; relative
bias = 3 %, −6 %, and −7 %; NRMSE = 47 %, 53 %, and 118 % for altitudes
between 40–500, 500–1500, and >1500 m, respectively)
is quite good considering the challenging environment and few opportunities
for assimilations of AOT from satellites during the campaign. Modeled
relative humidities (RHs) are negatively biased at all altitudes (absolute
bias =-5 %, −8 %, and −3 % for altitudes <500 500–1500
and >1500 m, respectively), motivating interest in the role of
RH errors in AOT and extinction simulations. Interestingly, NAAPS-RA AOT and
extinction agreement with the HSRL-2 does not change significantly (i.e.,
NRMSE values do not all decrease) when RHs from dropsondes are substituted
into the model, yet biases all move in a positive direction. Further
exploration suggests changes in modeled extinction are more sensitive to the
actual magnitude of both the extinction coefficients and the dropsonde RHs
being substituted into the model as opposed to the absolute differences
between simulated and measured RHs. Finally, four case studies examine how
model errors in RH and the hygroscopic growth parameter, γ, affect
simulations of extinction in the mixed layer (ML). We find NAAPS-RA
overestimates the hygroscopicity of (i) smoke particles from biomass burning
in the Maritime Continent (MC) and (ii) anthropogenic emissions transported
from East Asia. This work mainly provides insight into the relationship
between errors in modeled RH and simulations of AOT and extinction in a
humid and tropical environment influenced by a myriad of meteorological
conditions and particle types. These results can be interpreted and
addressed by the modeling community as part of the effort to better
understand, quantify, and forecast atmospheric conditions in SEA.