Boundary layer sources for the Asian anticyclone: Regional contributions to a vertical conduit

Abstract

The transport of air from the planetary boundary layer (PBL) into the Asian Summer Monsoon anticyclone is investigated using backward trajectories initiated within the anti‐cyclone at 100 mb and 200 mb during August 2011. Transport occurs through a well‐defined conduit centered over the southern Tibetan plateau, where convection lofts air parcels into the anticyclone. The conduit, as a dynamical feature, is distinct from the anticyclone. Thus, while the anticyclone influences transport through the upper troposphere and lower stratosphere, it does not by itself define a transport pipeline through that region. To quantify model sensitivities, parcel trajectories are calculated using wind fields from multiple analysis data sets (European Centre for Medium‐Range Weather Forecasts, National Center for Environmental Prediction's Global Forecasting System, and NASA's Modern‐Era Retrospective Analysis for Research and Applications [MERRA]) and from synthetically modified data sets that explore the roles of vertical motion and horizontal resolution for discrepancies among these calculations. All calculations agree on the relative contributions to PBL sources for the anticyclone from large‐scale regions with Tibetan Plateau and India/SE Asia being the most important. However, they disagree on the total fraction of air within the anticyclone that was recently in the PBL. At 200 mbar, calculations using MERRA are clear outliers due to problematic vertical motion in those data. Large differences among the different data sets at 100 mbar are more closely related to horizontal resolution. It is speculated that this reflects the importance of deep, small‐scale convective updrafts for transport to 100 mbar.

Dynamics and composition of the Asian summer monsoon anticyclone

“…1, 3). It has been suggested to be the main transport pathway of pollutants to the UT (Bergman et al, 2013;, which is supported by our simulation (Fig. 11) and the location of maximum moist static energy (Boos and Hurley, 2013).…”

“…It is stronger than other monsoon systems because of the topography of the region, which insulates warm, moist air over South Asia (the sub-Himalayan countries of the Indian subcontinent) from the cold and dry extratropics (Boos and Kuang, 2010). This leads to a global maximum of surface moist static energy at the south-western flank of the Himalayas (Boos and Hurley, 2013), which drives deep convective updraughts during Northern Hemispheric summer. Elevated surface heating over the Tibetan plateau (Flohn, 1960;Fu et al, 2006), predominantly northward surface winds plus orographic uplifting at the southern/south-western slopes of the Himalayas (Li et al, 2005;Y.…”

Quantifying pollution transport from the Asian monsoon anticyclone into the lower stratosphere

“…The higher fraction of air from the anticyclone edge compared to the core is likely a result of the larger area of the edge region. Note that air masses in the anticyclone edge may have originated in the anticyclone core at lower levels, as suggested by the vertical transport conduit pathway proposed by Bergman et al (2013). …”

“…Related to this transport are increased mixing ratios of trace gases with tropospheric sources and decreased mixing ratios of trace gases with stratospheric sources (e.g., Park et al, 2008). The detailed upward transport from the convective outflow to higher levels involves a vertical conduit over the southern Tibetan Plateau (Bergman et al, 2013). In addition, convective uplift by typhoons has been shown to inject air masses into the outer region of the anticyclonic circulation .…”

Analyzing dynamical circulations in the tropical tropopause layer through empirical predictions of cirrus cloud distributions

“…It is tempting to use this result to weigh in on the discussion regarding the relative merits of the kinematic formulation versus the diabatic and Lagrangian cold point) of cloud probability from four data sources: kinematic trajectories using MERRA temperature and winds (blue bars), diabatic trajectories using MERRA temperature, winds, and total diabatic heating rates (gray), kinematic trajectories using GFS temperature and winds (red), and kinematic trajectories using ERA-interim temperature and winds (black). Shown are explained variances during boreal summer formulation [Danielsen, 1961;Schoeberl et al, 2003;Ploeger et al, 2010Ploeger et al, , 2011Schoeberl and Dessler, 2011]; however, diabatic heating rates from MERRA have known weaknesses-particularly during summer [Bergman et al, 2013;Wright and Fueglistaler, 2013]. Furthermore, there is no significant difference in the cloud predictions by the four data sets during winter (not shown; seven-season averages of r 2 are in the range 0.90-0.91 for all four data sources).…”