A Study Of Stratosphere Troposphere Exchange And Tracer Transport

The stratosphere troposphere exchange (STE) and tracer transport directly influence the spatial distribution of atmospheric constitutes, and further impact on the atmospheric energy budget and circulation via the chemistry—radiation—dynamic interactions. Detailed investigations on the STE and tracer transport are important for understanding the stratosphere-troposphere coupling and the effect of stratospheric processes on the tropospheric weather and climate. Using a climate-chemistry model, reanalysis data and satellite measurements, the character of global spatial scale exchange and transport between stratosphere and troposphere are analysed and the effect of climate changes on the STE is investiaged in this thesis. In addition, the charateristics of tracer transport in the polar stratosphere are compared with those in the low-middle latitude stratosphere. The main conclusions are summarized as following:1. There are significant hemispheric differences in tracer transport properties at midlatitudes and high latitudes. The downward tracer transport in the northern midlatitude stratosphere is faster than at southern midlatitudes, whereas the descent is stronger in the southern polar region than in the north. On the global average, the fastest stratosphere-to-troposphere transport occurs in northern winter, while from August to October the downward transport from stratosphere is weakest. The maximum troposphere mean (TM) age-of-air derived from an age tracer released in the upper stratosphere can reach13years and is much larger than the maximum stratosphere mean (SM) age-of-air derived from the age tracer released from the troposphere, suggesting that tracer transport from the troposphere to stratosphere is more rapid than from the stratosphere to troposphere. The TM age-of-air in the Southern Hemisphere is older than in the Northern Hemisphere, indicating that the age tracer in the northern midlatitudes and high latitudes is transported down to the surface faster than in the southern midlatitude and high latitude.2. In the stratosphere, increased SSTs tend to accelerate upward transport because of enhanced upwelling from the troposphere. Changes in the SM age-of-air caused by uniform increases in SSTs are much smaller than those caused by the combined changes in SSTs and GHG values. Increased SSTs tends to slow the downward transport in the stratosphere and cause increases in the TM age-of-air. The larger SST increases give rise to a larger TM age-of-air in the stratosphere and a smaller TM age-of-air in the troposphere. Changes in the TM age-of-air caused by increased SSTs are larger in magnitude than corresponding changes in the SM age-of-air. However, the differences between increases in TM age-of-air in the stratosphere because of different SST and GHG increases are smaller than the differences between decreases in the SM age-of-air in the stratosphere caused by different SST and GHG increases. When both SST and GHG values are increased to the2100conditions, the tropical upwelling is enhanced by15%compared to the present-day conditions.3. The mechanisms for the occurrence of the double peak in the long-lived stratospheric tracers, i.e., CH4and N2O, and its connection with the stratospheric semiannual oscillation (SAO) and quasi-biennial oscillation (QBO) are investigated to explain the interannual variations in the stratopause double peak in CH4and N2O. It is found that douple peak distributions in HALOE CH4mixing ratio in April1993and1995are associated with the prominent first cycle of the SAO westerlies, which cause local vertical downwelling in the upper equatorial stratosphere. The sensitivity simulations of the Whole Atmosphere Community Climate Model version3(WACCM3) verified that gravity waves have a large contribution to the development and strength of the SAO westerlies. In addition, the deeper equatorial trough of the double peak is unlikely to always be accompanied by the more prominent Northern Hemispheric lobe. In fact, the Northern Hemispheric lobe of the double peak is attributed to subtropical upwelling, which is mainly affected by the SAO, QBO, and annual oscillation harmonics. The modeled equatorial chemical destruction of CH4shows a semiannual variation, with the minimum occurring when the first and second cycles of SAO westerlies are prevalent. However, the altitude of greatest chemical destruction is below the trough of the double peak, which is dominated by the advection and eddy transport.4. Based on model simulations, the effect of QBO and stratospheric final warming (SFW) on polar ozone and chemical constituents transport are analyzed. Due to the subtropical secondary upwelling induced by the QBO westerlies, the partial column ozone in the northern middle latitude stratosphere is relatively low. The patial column ozone in the northern polar stratosphere during westly QBO phase is about12DU lower than that during eastly QBO phase. The accumulated ozone depletion in the northern polar winter upper and lower stratosphere is larger during westly QBO phase than that during eastly QBO phase. The stronger ozone depletion in the northern polar lower stratosphere is likely associated with the lower temperature, which can lead to more polar stratospheric cloud (PSC) and heterogeneous ozone depletion in the lower polar stratosphere. In the northern polar upper stratosphere, where the temperature is warm enough so that the few PSC shaped, the higher temperature induced by the adiabatic heating from strengthened northern polar vortex descending motion results in more rapid gas-phase ozone reduction reactions. The statistical analysis reveals that the correlation coefficient between midlatitude and high latitude CH4anomalies at10hPa is0.55in the northern hemisphere stratosphere, while it is0.22in the southern hemisphere stratosphere. The simulated results show that the QBO has little impact on the onset date of the stratospheric final warming date. For early SFW events composites, the northern polar CH4mixing ratios in northern polar stratosphere show abrupt increases during the evolution time of SFW. After early SFW events occurred, CH4mixing ratios in the northern polar stratosphere are obviously enhanced. The partial column ozone in the northern polar stratosphere TCO increases continuously until days2-3after the early SFW events onset, and then decreases. For late SFW events with a later onset date, CH4mixing ratios in the northern polar stratosphere show a less significant variation during the evolution time of SFW events, and the partial column ozone in the northern polar stratosphere decreases before the onset of late SFW events.