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Long-lived vertically and horizontally stratified traces can be used to define a “coordinate system” for the interpretation of relationships among observed fields. A minimum complement of tracers such as coordinate system is CH4, N2O, CFC-11, CO2 and PV, the potential vorticity. The large dynamic range in the rate of removal of CH4, H2O, and CFC-11 above the tropopause coupled with high spatial resolution meridional transections of these species provide unique insight into processes involved in the production and destruction of tracer variance; CO2 mixing ratios establish the lifetime of air parcels (i.e., the time between entry of the air through the Hadley-driven tropopause and the time of observation) and PV distinguishes between a tracer that is it not transported across isentropes by diabatic circulation (PV) and ones that are (CH4, N2O, CFC-11). 

Question 2. What are the threshold conditions for significant repartitioning of reactive species within the nitrogen, chlorine, bromine, and hydrogen families?

The thrust of this question is to understand how the reactive compounds, most notably the catalytically active free radicals, respond to dropping temperatures that initiate polar stratospheric cloud formation both inside and within the environs of the vortex. 

• What is the mechanism for the “Noxon cliff” - the removal of NOx from the gas phase? Does the phenomenon require the presence of PSCs?

• What conditions (temperature, pressure, HONO2 and H2O vapor pressure) trigger the formation of PSCs? At what threshold temperatures do Type I and Type II PSCs form? Is temperature alone a valid indication of these phase transitions?

• Do NO, NO2, ClO, HONO2 and HCl concentration fields evolve in the temperature and PSC fields in a manner consistent with heterogenous conversion of HCl and HONO2 to gas phase Cl2 and solid phase nitric acid trihydrate? How important is the N2O5/H2O reaction in the denitrification process and in the repartioning of HOx and NOx radicals?

• Do PSCs appear outside the vortex, for example, in gravity wave events? How important are these localized adiabatic processes to the overall effectiveness of halogen and nitrogen repartitioning?

• Which processes govern the transition from “normal” conditions to deNOxification (removal of NOx from the gas phase), to denitrification (removal of NOy, from the gas phase), to dehydration (irreversible removal of H2O, in all phase)?

• What factors control the kinetics of HCl/ClONO2 conversion to ClO?

• What factors control growth rates and subsidence rates of PSCs?

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Transcription Notes:
Review mostly served to fix minor typos and issues with chemical symbols