Meteorological conditions and transport pathways during the Transport and Chemical Evolution over the Pacific (TRACE‐P) experiment

Abstract

The Transport and Chemical Evolution over the Pacific (TRACE‐P) experiment was conducted between February and April 2001. It included extensive chemical sampling by two aircraft based primarily in Hong Kong and Yokota Air Base, Japan. TRACE‐P examined pathways for the outflow of chemically and radiatively important gases and aerosols and their precursors from eastern Asia to the western Pacific and explored the chemical evolution of Asian outflow. This paper describes meteorological conditions and transport pathways over the Pacific Basin during TRACE‐P. Meteorological conditions changed rapidly during the period due to the seasonal winter to spring transition and the decay of prolonged ENSO cold phase (La Nina) conditions. To document these changes, TRACE‐P was divided into two halves, and mean flow patterns during each half are presented and discussed. Important circulation features are the semipermanent Siberian anticyclone and transient middle latitude cyclones that form near eastern Asia and then move eastward over the northern Pacific. Five‐day backward trajectories from the various flight tracks show that air sampled by the aircraft had been transported from a variety of locations. Some parcels remained over the tropical western North Pacific during the entire period, while other important origins were Southeast Asia, Africa, and central Asia. Specifically, lower tropospheric flight segments out of Hong Kong sampled both prefrontal maritime air as well as postfrontal air from the Asian continent. Conversely, low‐level flight segments out of Yokota, Japan mostly sampled postfrontal Asian air. Southern portions of middle and upper tropospheric flight segments from Hong Kong sampled air previously in the deep tropics, while the more northerly flight segments sampled air that originated from the west (e.g., passing over central Africa and India). Most upper level flight segments from Yokota sampled air arriving from the west. Patterns of satellite‐derived precipitation and lightning are described. TRACE‐P occurs during a neutral to weak La Nina period of relatively cold sea surface temperatures in the tropical Pacific. Compared with climatology, the TRACE‐P period exhibits deep convection located west of its typical position; however, tropospheric flow patterns do not exhibit a strong La Nina signal. Circulation patterns during TRACE‐P are found to be generally similar to those during NASA's PEM WEST‐B mission that occurred in the same region during February–March 1994.

The Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) mission: design, execution, and first results

“…Further context was provided by previous NASA aircraft campaigns along the Asian Pacific Rim in spring 1994 (PEM-West B; Hoell et al, 1997) and spring 2001 (TRACE-P; Jacob et al, 2003), and over the Northeast Pacific and southern Alaska in spring 2006 (INTEX-B; Singh et al, 2009). PEM-West B and TRACE-P observed frequent lifting of Asian pollution in WCBs followed by northeastward transport toward the Arctic in the general direction of Alaska (Fuelberg et al, 2003). This led to the selection of Fairbanks, Alaska as the main operational base for the ARCTAS-A spring deployment, and an overnight base in Thule, Greenland to achieve broader spatial coverage.…”

Analysis of CCN activity of Arctic aerosol and Canadian biomass burning during summer 2008

“…An extensive overview and description of the mission is given by Jacob et al (2010) and the accompanying detailed meteorological overview and modeled air mass back trajectories is provided by Fuelberg et al (2010 The primary objective of ARCTAS-B was to investigate and characterize fresh boreal forest fire emissions in Canada, as well as their evolution and transport into the Arctic environment. A majority of the aerosol sampling occurred within the boundary layer and lower free troposphere, with fresh biomass burning emissions sampled primarily in the boundary layer within a few hours after emission.…”

“…The transport of pollution from midlatitude continents can occur throughout the year, but occurs most frequently during the winter-spring transition, when increased cyclonic activity enables the pollution to be transferred along warm conveyor belts into the vertically stratified Arctic atmosphere (Shaw, 1995;Stohl, 2001;Fuelberg et al, 2003;Scheuer et al, 2003;Quinn et al, 2007). These Arctic haze layers can persist for weeks and have been attributed to both industrial sources (Law and Stohl, 2007) and biomass burning Quinn et al, 2008;Warneke et al, 2009Warneke et al, , 2010.…”

Boundary‐layer ventilation by baroclinic life cycles

“…Bethan et al, 1998;Cooper et al, 2001;Li et al, 2002;Stohl et al, 2003;Huntrieser et al, 2005) and across the Pacific basin (e.g. Fuelberg et al, 2003;Cooper et al, 2004;Mari et al, 2004) have been conducted and results show that WCBs are capable of transporting pollution large distances in both ocean basins. However, uncertainties in the efficiency of conveyor belt flows (and convective activity) to transport pollution out of the boundary layer remain.…”