An Analysis Of Stratosphere Troposphere Exchange And Stratospheric Water Vapor And Ozone

Compared to researches on tropospheric weather and climate, the studies of stratospheric processes are relatively fewer. In recent years, with the improvement of space exploration technology and development of numerical models for the middle atmosphere, more and more attentions have been paid on stratospheric processes. Focused on some hot topics of the stratosphere research, a comprehensive study on stratosphere troposphere exchange (STE) and its effect on stratospheric water vapor is carried using a general circulation model and a state-of-art chemistry-climate model outputs data, satellite observations, European Center for Medium range Weather Forecasting (ECMWF) 40 years reanalysis data and National Centers for Environmental Prediction (NCEP) reanalysis-2 data. The effects of stratospheric water vapor changes and greenhouse gases (GHGs) emissions changes on stratospheric ozone are also analysed. The main conclusions are as following:(1) The potential radiative impact of ozone changes on stratosphere-troposphere exchange (STE) is investigated by a series of general circulation model (GCM) simulations. The impact of an arbitrary 15% O3 change on temperature and cross-tropopause mass flux is compared to the corresponding effect of CO2 doubling. Our analysis shows that a 15% global O3 decrease can cause a maximum cooling of 2.4 K in the stratosphere and-7.2% increase in the tropical upwelling. A global 15% O3 increase gives rise to-2.1 K stratospheric warming and-4% decrease in the tropical upwelling. The effect of a±15% change in O3 below 100 hPa is relatively small. However, the effect of a 15% O3 increase between 200-70 hPa is similar to that of a 15% O3 increase through the whole model domain, suggesting that ozone increases in the UTLS dominate the impact on temperature and tropical upwelling. Sea-surface temperature (SST) changes associated with increasing atmospheric GHGs have a profound impact on the STE. Without corresponding SST changes, the radiative effects of the CO2 doubling on the STE are less significant than a global 15% O3 increase. When the SST changes are considered in the doubled CO2 experiment, the tropical upwelling is significantly increased (by 20.4%).(2) The potential radiative impacts of ozone changes on tropopause, which directly influence stratospheric water vapor, are investigated by a series of general climate model (GCM) simulations. The impacts of an arbitrary 15% O3 change on the tropopause and stratospheric water vapor are compared to the corresponding effects from a doubling of atmospheric CO2. Our analysis shows that a 15% global O3 decrease can results in a higher tropical tropopause and lower tropopause temperatures, and hence less stratospheric water vapor and smaller amplitude of the so-called tape recorder signal. A global 15% O3 increase gives rise to more water vapor entering the stratosphere due to a lower tropopause and higher tropopause temperatures. When the SST changes are considered in the doubled CO2 experiment, the stratospheric water vapor is significantly increased with a much higher, but warmer, tropopause. Without corresponding SST changes, the radiative effects of the CO2 doubling on the stratospheric water vapor are less significant.(3) Using the ECMWF/NCEP reanalysis data, satellite observations from AURA MLS and UARS HALOE, and Oceanic Nino Index (ONI) data, the effects of El Nin-o and La Nin-a events on the stratospheric water vapor changes are investigated. Overall, El Nin-o events tend to moisten the lower stratosphere but dry the middle stratosphere. La Nin-a events are likely to dry the lower stratosphere over a narrow band of tropics (5°S-5°N) but have a moistening effect on the whole stratosphere when averaged over a broader region of tropics between 25°S-25°N. The moistening effect of La Nin-a events mainly occurs in lower stratosphere in the southern hemisphere tropics where a significant 20% increase in the tropical upwelling is caused by La Nin-a events. El Nin-o events have a more significant effect on the tropical upwelling in the northern hemisphere extratropics than in southern hemisphere extratropics. The net effect of ENSO activities on the lower stratospheric water vapor is stronger in the southern hemisphere tropics than in the northern hemisphere tropics.(4) Using a state-of-the-art, fully coupled chemistry climate model-Whole Atmosphere Community Climate Model 3 (WACCM3), the impact of increasing surface emissions of methane (CH4) on stratospheric water vapor is investigated. Relative to 2000 surface emissions of GHGs, a 50% increase in CH4 surface emissions causes an average increase of 0.8 ppmv water vapor in the stratosphere. The radative effect of increased CH4 on the tropopause contributes 12% to the stratospheric water vapor increases, and the chemical process explains the rest of 88%. The oxidation of CH4 into water vapor is more efficient in the southern hemisphere than in the northern hemisphere. In the northern hemisphere:1 mol CH4 molecule→1.63 mol H2O molecule; in the southern hemisphere:1 mol CH4 molecule→1.82 mol H2O molecule.(5) Using a state-of-the-art, fully coupled chemistry climate model WACCM3, the impact of increasing surface emissions of methane (CH4) on ozone is investigated. Relative to the 2000 surface emissions of GHGs, a 50% increase in the CH4 emission would lead to an overall increase of total column ozone (TCO) by-3% at the lower-mid latitudes as well as at the northern high latitudes, and a maximum increase of -8% at the southern high latitudes. In the northern hemisphere mid-high latitudes, the direct and indirect impacts of CH4 increases tend to increase TCO (Here, the indirect impact referes to the impact of water vapor increases caused by oxidation of CH4. The direct impact referes to the impact of increased CH4 on ozone by itself). However, in the northern hemisphere lower latitudes and the whole southern hemisphere the TCO increases are mostly due to the direct impact. It is worth to note that a 50% increase in CH4 surface emission is capable of causing a significant increase of TCO over Antarctic in southern Spring, with a maximum growth rate of up to-20%. It is found that the significant TCO increase is mainly caused by the chemical effect and the dynamical effect plays a second role. The radiative effect of CH4 increases on the stratospheric ozone increase is small.