TY - JOUR

T1 - Diagnosing the stratosphere-to-troposphere flux of ozone in a chemistry transport model

AU - Hsu, Juno

AU - Prather, M J

AU - Wild, O

PY - 2005/10/12

Y1 - 2005/10/12

N2 - [1] Events involving stratosphere-troposphere exchange (STE) of ozone, such as tropopause folds and westerly ducts, are readily identified in observations and models, but a quantitative flux specifying where and when stratospheric ozone is mixed into the troposphere is not readily discerned from either. This work presents a new diagnostic based on determining when stratospheric air is mixed and diluted down to tropospheric abundances (< 100 ppb) and hence effectively participates in tropospheric chemistry. The method is applied to two years of high-resolution, global meteorological fields (1.9 degrees, 40 levels) from the ECMWF forecast model derived by U. Oslo for chemistry transport modeling and used in TRACE-P studies. The UCI CTM is run here with linearized stratospheric ozone chemistry (Linoz) and a parameterized tropospheric sink. In terms of events, the CTM accurately follows a March 2001 westerly duct stratospheric intrusion into the tropical eastern Pacific as observed by TOMS and calculates a 48-hour burst of STE O3 flux for that region. The influx associated with the event (0.3 Tg) is much less than the anomalous amount seen as an isolated island in column ozone (1.7 Tg). A climatology of monthly mean STE fluxes is similar for both years ( January to December 1997 and May 2000 to April 2001), but the warm phase of ENSO December 1997 is distinctly different from the cold phase of ENSO month December 2000. Global ozone fluxes are about 515 Tg ( year 1997) and 550 Tg ( year 2000/ 2001) with an equal amount into each hemisphere, and larger springtime fluxes for both hemispheres. In terms of geographical distribution, Northern Hemisphere regions of high ozone flux follow the jet streams over the oceans in the winter and over the continents in the summer, in agreement with many previous studies. In contrast, we find the largest STE flux is located in the subtropics during late spring, particularly over the Tibetan Plateau in May. This hot spot of STE is not a numerical artifact, it occurs in both meteorological years, and it appears to be caused by the rapid erosion of the tropopause. Ozone fluxes in the SouthernHemisphere have less variability ( either temporal or spatial), and they occur mainly in the subtropical region (25 degrees S - 35 degrees S) regardless of season. The poles, throughout the year, show minimal STE O3 flux.

AB - [1] Events involving stratosphere-troposphere exchange (STE) of ozone, such as tropopause folds and westerly ducts, are readily identified in observations and models, but a quantitative flux specifying where and when stratospheric ozone is mixed into the troposphere is not readily discerned from either. This work presents a new diagnostic based on determining when stratospheric air is mixed and diluted down to tropospheric abundances (< 100 ppb) and hence effectively participates in tropospheric chemistry. The method is applied to two years of high-resolution, global meteorological fields (1.9 degrees, 40 levels) from the ECMWF forecast model derived by U. Oslo for chemistry transport modeling and used in TRACE-P studies. The UCI CTM is run here with linearized stratospheric ozone chemistry (Linoz) and a parameterized tropospheric sink. In terms of events, the CTM accurately follows a March 2001 westerly duct stratospheric intrusion into the tropical eastern Pacific as observed by TOMS and calculates a 48-hour burst of STE O3 flux for that region. The influx associated with the event (0.3 Tg) is much less than the anomalous amount seen as an isolated island in column ozone (1.7 Tg). A climatology of monthly mean STE fluxes is similar for both years ( January to December 1997 and May 2000 to April 2001), but the warm phase of ENSO December 1997 is distinctly different from the cold phase of ENSO month December 2000. Global ozone fluxes are about 515 Tg ( year 1997) and 550 Tg ( year 2000/ 2001) with an equal amount into each hemisphere, and larger springtime fluxes for both hemispheres. In terms of geographical distribution, Northern Hemisphere regions of high ozone flux follow the jet streams over the oceans in the winter and over the continents in the summer, in agreement with many previous studies. In contrast, we find the largest STE flux is located in the subtropics during late spring, particularly over the Tibetan Plateau in May. This hot spot of STE is not a numerical artifact, it occurs in both meteorological years, and it appears to be caused by the rapid erosion of the tropopause. Ozone fluxes in the SouthernHemisphere have less variability ( either temporal or spatial), and they occur mainly in the subtropical region (25 degrees S - 35 degrees S) regardless of season. The poles, throughout the year, show minimal STE O3 flux.

KW - TROPICAL UPPER TROPOSPHERE

KW - AIR-MASS CHARACTERISTICS

KW - TRACE CONSTITUENTS

KW - 3-D MODELS

KW - EXCHANGE

KW - TROPOPAUSE

KW - CLIMATOLOGY

KW - PACIFIC

KW - DISTRIBUTIONS

KW - INTRUSIONS

U2 - 10.1029/2005JD006045

DO - 10.1029/2005JD006045

M3 - Journal article

VL - 110

SP - -

JO - Journal of Geophysical Research: Atmospheres

JF - Journal of Geophysical Research: Atmospheres

SN - 0747-7309

IS - D19

M1 - D19305

ER -