عنوان مقاله [English]
Radiation input from the Sun is the source of energy for the Earth’s climate system (Hartmann, 1994). Most of the solar radiation absorbed at the surface, the rest is absorbed by the atmosphere. The global temperature profile of the atmosphere reflects a balance between the radiative, convective, and dynamical heating/cooling of the surface-atmosphere system. Understanding of the climate change in recent decades is important for the prediction of the future climate. Observed modifications in the vertical temperature structure of the atmosphere have been proposed as a primary indicator of climate change (Marshal, 2002). Radiosonde data are the primary source for monitoring changes in upper-air parameters. The second source is satellite-derived data from the microwave-sounding unit (MSU). Third source of ‘‘observed’’ upper-air data are the reanalysis projects as NCEP/NCAR and ECMWF. In this study, we attempt to estimate trends in the Irans surface and upper atmosphere temperature as an index of climate change on the basis of ECMWF data, which offer substantially higher vertical resolution than radiosounds and the microwave sounding unit (MSU), thus allowing a more accurate identification of the upper atmosphere and possible multiple upper atmosphere levels. In addition, the tempo-spatial resolution of applied data is higher than other data sources.
The monthly surface and upper atmospheric air temperature data of Iran during 1/1979 to 4/2014 extracted from European Centre for Medium-Range Weather Forecasts (ECMWF). The spatial resolution 0.125 degree has been applied. Based on selected spatial resolution, 9965 pixels located on the Iran political boundry. The variation of spatial mean air temperature over Iran from surface to 10 hPa was analyzied. The radiosonds recorded air temperature from 11 upper stations over Iran compared to the ECMWF data to evaluate accuracy of applied data. Two non parametric tests of Mann-Kendal and Sen,s estimatotor used to decide about significancy of trend and slope of trend respectively.
The results of this study show that using ECMWF data to evaluate varation of surface and upper atmospheric air temperature is useful. The tempo-spatial resolution of applied data is very high in horizontal and vertical. This implies that the ECMWF data do a reasonable job of capturing the variability of upper atmospheric temperature and are more adequate rather than Microwave Sounding Unit (MSU) and radiosounds data. The results also show that trend of surface and upper atmospheric air tempertre is significant at 95% confidence level. The observed trend near the earth surface and low and high troposphere is positive while is negative in the stratosphere. Althoght the trend of Iran’s middle troposphere layer temperature is not significant statistically at the 95% but fitting regression line on the standardized air temperature time series show that trend is positive. The slope rate of Iran’s surface temperature is 0.65°C per decades and is higher that other levels. The observed warming rate in the lower troposphere is higher than upper troposphere. The spatial distribution of the trend slope near the surface show that the highest warimimg observed between 34 to 37 latitudes. In the southern parts of Alborz and eastern parts of Zagros, the slope rate of surface temperature rate is 1.3 to 1.6 degrees C per decade.
The obsereved increased tropospheric temperature and cooling of stratosphere is in good agreement with previous studies findings. The temperature change near the surface and lower troposphere is high in the semi northern parts of the country. The rate of upper troposphere temperature is not significant in the semi northern parts. The increase of upper troposphere temperature in the southern parts results in change tropopouse height. The depletion of ozone in the stratosphere (upper atmosphere) maybe contributing to the cooling of the stratosphere layer. The increased man made pollutants, green house gases and ozone in troposphere is also contributing to the warming of the troposphere. In temporal view from 1998, a positive anomay in temperature is observed near the surface and lower troposphere. The highest warming occurred in 2010 and 2001. According to other researchers finding warming of troposphere results in the displacement of Hadley cells and subtropical jet streams towards north and changes in tropical circulation patterns.