Study On The Effect Of Solar Activity And Human Emission Variation On Atmospheric Circulation And Temperature

Solar activities and human emission changes can influence the climate of stratosphere and troposphere directly. Detailed investigations on the effect of the11-yr solar cycle and emission changes of varous gases, especially greenhouse gas (GHG) emission increases over the East Asia, on the circulation, temperature and ozone in the stratosphere and troposphere, are important for better understanding the dynamic-radiation-chemistry interactions between the stratosphere and troposphere and future climate change. Using a climate-chemistry model and reanalysis data, the effect of the11-yr solar cycle and emission increases of NOx, CH4and N2O over the East Asia on the circulation, temperature and ozone in the stratosphere and troposphere are investiaged in this thesis. The main conclusions are summarized as following:1. We have used a fully coupled chemistry-climate model (WACCM) to investigate the relative importance of the direct and indirect effects of lla solar variations on stratospheric temperature and ozone. Although the model does not contain a quasi-biennial oscillation (QBO) and uses fixed sea surface temperature (SST), it is able to produce a second maximum solar response in tropical lower stratospheric (TLS) temperature and ozone of approximately0.5K and3%, respectively. In the TLS, the solar spectral variations in the chemistry scheme play a more important role than solar spectral variations in the radiation scheme in generating temperature and ozone responses. The chemistry effect of solar variations causes significant changes in the Brewer-Dobson (BD) circulation resulting in ozone anomalies in the TLS. The model simulations also show a negative feedback in the upper stratosphere between the temperature and ozone responses. A wavelet analysis of the modeled ozone and temperature time series reveals that the maximum solar responses in ozone and temperature caused by both chemical and radiative effects occur at different altitudes in the upper stratosphere. The analysis also confirms that both the direct radiative and indirect ozone feedback effects are important in generating a solar response in the upper stratospheric temperatures, although the solar spectral variations in the chemistry scheme give the largest solar cycle power in the upper stratospheric temperature. 2. The some responses of tropical tropospheric temperature and the tropical eastern Pacific sea level pressure (SLP) to the11-yr solar cycle can be simulated by the WACCM3with fixed SST. The response of the tropical tropospheric temperature in winter is negative and is positive in summer, with an amplitude of0.1K. The results above are in accordance with the findings in some prevous observational and modeling studies. Because of the fixed SST, the SST anomalies at the tropical eastern Pacific can’t be simulated, but the SLP anomalies over the tropical eastern Pacific can be simulated. The resoponses of tropospheric climate to the11-yr solay cycle are accommodated by the’bottom-up’mechanism, which is caused by the11-yr solar cycle in the radiation scheme. The tropical tropospheric ozone anomalies are negative in solar maximum years relative to solar minimum years because more OH is generated in the troposphere during solar maximum years and the tropospheric ozone decreses by3%in the solar maximum years which is caused by both the direct radiative and indirect chemistry effects of solar variations.3. The WACCM3is used to investigate the response of the CH4increases on climate. It is found that CH4emission increases can strengthen the westerly winds at the northern hemisphere mid-latitudes, accelerate the BD circulation and increase the mass flux through the tropospause. However, the increases of CH4emission in different regions lead to different changes of BD circulation. The tropical BD circulation becomes weaker when CH4emission is increased over the East Asia and becomes stronger when CH4emission is increased over the North America between10°S-10°N at100hPa. When the CH4emission is increased by50%at the East Asia and15%over the global, the stratospheric temperature cools up to0.15K, the stratospheric ozone increases45ppbv and60ppbv, respectively. An increase of CH4emission by50%over the East Asia has a greater influence on the stratospheric ozone than the effect of CH4emission increase of the same amount over the North America. CH4increases over the East Asia and the North America can reduce the tropospheric OH concentration and increase the tropospheric ozone concentration at the northern mid-latitudes. The maximum changes of the tropospheric ozone caused by CH4emission increases over the East Asia and the North America appear at different months. When CH4is increased over the East Asia, the increase of troposphere ozone concentration is largest in August. When CH4is increased over the North America, the increase of ozone concentration at mid troposphere is largest in July. When CH4emission is increased over the East Asia, its impact on the tropospheric ozone can be noted throughout the troposphere. However, when CH4emission is increased over the North America, its impact on the tropospheric ozone can be noted only in the lower troposphere.4. A comparison of the effect of a50%increase of CH4emission with the effect of a50%increase in NOx emission over the East Asia reveals that the stratospheric temperature and ozone changes caused by CH4and NOx emission increases are smaller. However, a50%increase in NOx emission over East Asia can cause a2%increase in the tropospheric ozone over East Asia. When CO2emission is increased by50%globally, it will cause the troposphere warming and stratospheric cooling, and ozone increases in both the troposphere and stratosphere. The circulation changes caused by a50%CO2increase are much larger than that caused by a50%increase of CH4or NOx emissions. When N2O emission is increased by50%globally, there is no significant impact on the tropospheric ozone and temperature, but it has a significant effect on the stratospheric ozone and temperature which causes ozone decreases and temperature decreases in the stratosphere. The increases in CH4, NOx, N2O and CO2emissions can strengthen westerly winds, accelerate the BD circulation at the mid latitudes, especially at the northern hemisphere mid-latitudes and the cross tropopause mass flux du to the BD circulation also increases.5. The coupled chemistry-climate model WACCM3(Whole Atmosphere Community Climate Model) is applied to study the seasonal variations of the stratospheric temperature, wind, ozone and radiation fields. The stratospheric Quasi-Zero Wind Layer at around20-22km (i.e.,30-50hPa), where the wind speed is less than5m/s and is stable north of40°N during July and August, is suitable for long-term stay of airships. There appears a belt of ozone at30hPa over the China and ozone concentrations are greater in the mid-latitudes than in the lower latitudes below30hPa. There are significant seasonal spatial variations in solar heating rates in the stratosphere. In the upper stratosphere, the maximum solar heating rate reaches100×10-6K/s while in the lower stratosphere the maximum solar heating rate is only10×10-6K/s. The solar heating rate is greater in June to August than in September in China. The solar heating rate is greater in the mid-latitudes than in the lower latitudes between100hPa and30hPa and is greater in the lower latitudes than in the mid-latitudes above30hPa. The change of solar heating rate is small in August and September at30hPa and40hPa. The maximum diurnal variation of solar heating rate appears at40°N at30hPa. At50hPa, the diurnal variation of solar heating rate is smaller than that at40hPa and the maximum variation occurs farther south. The longwave heating rate is smaller in the lower latitudes than in the mid-latitude stratosphere. In particular condition of terrain, the ozone concentration, solar heating rate and longwave heating rate are smaller over Tibetan Plateau than other areas at the same latitude.