On the life cycle of a stratospheric intrusion and its dispersion into polluted warm conveyor belts

Abstract

The aircraft‐based 2002 Intercontinental Transport and Chemical Transformation experiment intercepted and chemically analyzed pollution plumes transported from Asia to the western United States. The research flight on 10–11 May 2002 detected mixing between polluted and stratospheric air at midtropospheric levels above the California coast. This study uses a Lagrangian domain‐filling trajectory technique to illustrate that this event was the result of mixing between two warm conveyor belts (WCB) containing Asian pollution and the remnants of a deep tropopause fold from a downstream midlatitude cyclone (referred to as the stratospheric component of a dry airstream or SCDA). Advection of the trajectory particles shows how the SCDA decayed over 7.5 days. One component dispersed into a downstream WCB, while another component descended into the lower troposphere and became entrained by an upwind WCB. After 7.5 days of transport 22% of the SCDA mass was transported into the troposphere. The portions of the SCDA that penetrated to the lowest altitudes had the greatest likelihood of being transported into the troposphere. For example, over 90% of the SCDA at altitudes below the 600 hPa level was transported to the troposphere, but none of the mass at the 200 hPa level was exchanged. More than half of the exchange occurred during the first 48 hours as the deepest portions of the tropopause fold decayed over the Pacific. The rest of the exchange occurred over the following 5.5 days as the remnants of the SCDA sheared apart along the edge of the stratospheric polar vortex and became entrained into subsequent tropopause folds and vortex breakaway features. Stratosphere to troposphere exchange resulted in the transport of 0.5 Tg of stratospheric ozone to the troposphere during the 7.5 day study period. Roughly half of the SCDA particles that entered the troposphere dispersed into the upwind and downwind WCBs.

Ozone profile retrievals from the Ozone Monitoring Instrument

“…The cross sections also clearly indicate significant stratospheric influences, even in regions of pollution transport, as many high ozone features are well connected to high ozone above. The coexistence of stratospheric intrusion with transport of pollution is consistent with the findings of Cooper et al (2004a, b) that stratospheric air masses often mix with pollution plumes in regions of continental outflow. In the above example, on 9 May, part of the pollution plume reached the west coast of the US.…”

“…Some of these ozone enhancements will reflect the transport of industrial pollution from the continents; this have been shown from many modeling studies (Parrish et al, 1993;Lelieveld et al, 2002;Liu et al, 2003;Duncan and Bey, 2004;Auvray and Bey, 2005;Li et al, 2005;Cooper et al, 2007). Some of these features could also be caused by stratospheric intrusions (Cooper et al, 2004a(Cooper et al, , 2005. For example, Fig.…”

“…9b shows the transport of high ozone from the stratosphere to the middle troposphere at 150 • W, associated with a tropopause folding as seen from the NCEP tropopause. Due to limited vertical resolution and the fact that pollution plumes from continental outflows often mix with stratospheric air masses (Cooper et al, 2004a(Cooper et al, , 2005, it is difficult to identify the origins of these high ozone features from OMI retrievals alone. It is necessary to use other in-situ observations, model simulations, and meteorological fields to assist with the interpretation of OMI retrievals.…”

Seasonality of ⁷Be concentrations in Europe and influence of tropopause height

“…Cooper et al, 2004). In this sense, previous studies using, among others, also 7 Be as a tracer of stratospheric air in the troposphere (Zanis et al, 1999;Cristofanelli et al, 2003Cristofanelli et al, , 2006 have demonstrated that air parcels originating in the stratosphere may reach the surface levels in two ways: (1) directly (less than about 2 d), through a vigorous vertical transport, and with largely conserved chemicalÁphysical properties after intrusion into the troposphere, and (2) indirectly (about 4Á5 d), through a multistep transport process, and a greater loss of stratospheric properties along the path.…”

Seasonal variations of CO2 near the tropopause observed by commercial aircraft

“…Concentrations of chemical species in the lower stratosphere are also perturbed by the cross-tropopause mixing. Mesoscale mixing events such as the mid-latitude tropopause folds and deep tropical convection have been recognized to play a significant role in the transport and mixing of mass and chemical species across the tropopause [Stohl et al, 2003;Cooper et al, 2004]. Many model studies have been conducted to estimate the seasonality of the transport, as well as the magnitude and spatial extent of the stratosphere-troposphere exchange [e.g., Chen, 1995;Haynes and Shuckburgh, 2000;Sprenger and Wernli, 2003].…”