Aerosol meteorology of Maritime Continent for the 2012 7SEAS southwest monsoon intensive study – Part 2: Philippine receptor observations of fine-scale aerosol behavior
The largest 7 Southeast Asian Studies (7SEAS) operations period within the
Maritime Continent (MC) occurred in the August–September 2012 biomass
burning season. Data included were observations aboard the M/Y
Vasco, dispatched to the Palawan Archipelago and Sulu Sea of the
Philippines for September 2012. At these locations, the Vasco
observed MC smoke and pollution entering the southwest monsoon (SWM)
monsoonal trough. Here we describe the research cruise findings and the finer-scale aerosol meteorology of this convectively active region. This 2012
cruise complemented a 2-week cruise in 2011 and was generally consistent with
previous findings in terms of how smoke emission and transport related to
monsoonal flows, tropical cyclones (TC), and the covariance between smoke
transport events and the atmosphere's thermodynamic structure. Biomass
burning plumes were usually mixed with significant amounts of anthropogenic
pollution. Also key to aerosol behavior were squall lines and cold pools
propagating across the South China Sea (SCS) and scavenging aerosol particles
in their path. However, the 2012 cruise showed much higher modulation in
aerosol frequency than its 2011 counterpart. Whereas in 2011 large synoptic-scale aerosol events transported high concentrations of smoke into the
Philippines over days, in 2012 measured aerosol events exhibited a much
shorter-term variation, sometimes only 3–12 h. Strong monsoonal flow
reversals were also experienced in 2012. Nucleation events in cleaner and
polluted conditions, as well as in urban plumes, were observed. Perhaps most
interestingly, several cases of squall lines preceding major aerosol events
were observed, as opposed to 2011 observations where these lines largely
scavenged aerosol particles from the marine boundary layer. Combined, these
observations indicate pockets of high and low particle counts that are not
uncommon in the region. These perturbations are difficult to observe by
satellite and very difficult to model. Indeed, the Navy Aerosol Analysis and
Prediction System (NAAPS) simulations captured longer period aerosol events
quite well but largely failed to capture the timing of high-frequency
phenomena. Ultimately, the research findings of these cruises demonstrate the
real world challenges of satellite-based missions, significant aerosol
life cycle questions such as those the future Aerosol/Clouds/Ecosystems (ACE)
will investigate, and the importance of small-scale phenomena such
as sea breezes, squall lines, and nucleation events embedded within SWM
patterns in dominating aerosol life cycle and potential relationships to
clouds
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