Ozone and tracer transport variations in the summer northern hemisphere stratosphere (original) (raw)

2001, Journal of Geophysical Research: Atmospheres

Constituent observations from the Upper Atmosphere Research Satellite (UARS) in combination with estimates of the residual circulation are used to examine the transport and chemical budgets of HF, CH4 and 03 in the summer Northern Hemisphere. Budget calculations ofHF, CH4 and 03 show that the transport tendency due to the residual circulation increases in magnitude and is largely opposed by eddy motions through the summer months. Ozone budget analyses show that between 100 and 31 hPa, the magnitudes of the mean circulation and eddy transport tenns increase through the summer months, producing tendencies that are factors of 2 to 3 times larger than the observed ozone change in the stratosphere. Chemical loss dominates the observed ozone decrease only at the highest latitudes, poleward of about 70øN. A comparison of observations from the Total Ozone Mapping Spectrometer with UARS-calculated total ozone suggests that poleward of 50øN, between 35% and 55% of the seasonal ozone decline during the summer occurs at altitudes below 100 hPa. The overall uncertainties, associated primarily with calculations of the residual circulation and eddy transport, are relatively large, and thus prevent accurate and useful constraints on the ozone chemical rate in the lower stratosphere. ozone must be well understood before accurate assessments of Copyright 2001 by the American Geophysical Union. Paper number 2001JD900004. 0148-0227/01/2001 JD900004509.00 anthropogenic processes can be made. Therefore it was recognized that a concerted effort must be made to study and assess the accuracy of the ozone budget in this region of the atmosphere. The focus of this paper will be to further examine transport variations in the summer NH stratosphere and assess how well we can constrain the budget terms using available tracer and circulation fields. The summer hemisphere has generally been characterized as a region of weak meridional circulation [Brasseur and Solomon, 1986; Luo et al., 1997]. Because topographically forced largescale planetary waves cannot propagate through the prevailing easterly winds present in the summer hemisphere [Charhey and Drazin, 1961], eddy wave activity is relatively weak. Statistics from the National Centers for Environmental Prediction (NCEP) analysis show that amplitudes of wave 1-3 geopotential height are significantly weaker from June through September in the NH midlatitudes [Randel, 1987]. Previous observations of tracer variability in the summer stratosphere have been explained as either remnants of the springtime final warming or normal mode wave oscillations [Ehhalt et al., 1983; Hess and Holton, 1985]. The variations in ozone and other trace gases in the summer stratosphere have been studied using various approaches. Results from a two-dimensional (2-D) model indicate that poleward of 40øN from 15 to 30 km, the net ozone loss during summer is due to photochemical destruction. This is attributed to the increased effectiveness of the odd nitrogen catalytic cycle [Perliski et al., 1989; Gao et al., 1999]. At lower latitudes, production and destruction are balanced by transport, while at higher altitudes, ozone is in photochemical equilibrium. However, the recent analysis of Rosenlof [1999] suggests that the seasonal cycle in transport is an important contributor to the summertime ozone budget between 60 ø and 70øN in the lower stratosphere.