A Study Of The Long-term Trends Of Brightness Temperature Based On Microwave Sounding Data

Due to shortage of observational data, the research on the long term variation trend of atmospheric temperature has been a problem that puzzles the climate scientists, and it is also the focus and difficulty of climate research. Satellite observation of global coverage resolved the sounding data uneven spatial distribution problem largely. In late 1960s, with the use of a series of Polar Orbiting Meteorological Satellite TIROS-N, satellite microwave temperature data has been accumulated for up to 35 years. The paper adopted MSU/AMSU-A STAR V3.0 brightness temperature data from NOAA researched from 1978 to 2013, through introducing a set of Ensemble Empirical Mode Decomposition (EEMD) method, focused research on non-linear trend of upper atmospheric brightness temperature, particularly focused on time evolution characteristics of brightness temperature climate trend, and did comparative study with classical linear regression (CLR) method. The results showed that:Linear trend calculated by CLR method showed that global average mid troposphere atmospheric warming rate was 0.11 K/10a and upper troposphere warming rate was 0.04 K/10a, lower stratospheric cooling rate was-0.31K/10a.Global average non-linear trend calculated by EEMD method showed that after 2000, Global warming is obviously slowed down or even hiatus, the warming hiatus mainly occurred in the northern hemisphere in troposphere. And the middle troposphere temperature is still warming in the southern hemisphere. The lower stratospheric temperature showed cooling trend.Linear and non-linear variation of zonal mean brightness temperature showed that warming was not uniform, and in the troposphere the warming (or cooling) rate was much higher than that in the middle and lower latitudes. Over the past 10 years, the intensity and scope of warming had decreased in the northern hemisphere. The middle layer of troposphere in the Antarctic region and the lower stratosphere gradually turned into warming trend from cooling. The cooling of stratosphere mainly occurred in lower and middle latitudes.Temporal-spatial evolution characteristics of global brightness temperature nonlinear trend showed that:in northern hemisphere, Arctic warming passed through the whole layer of atmosphere from top to bottom, but warming was slowed down in recent 10 years, and warming stagnant time occurred in upper and lower layers was not entirely consistent. Cooling in stratosphere was strongest in the mid latitude region, and cooling trend affected the lower atmosphere. So in recent years, trend of local cooling showed in the middle latitudes partly. The warming in Arctic and the cooling in the two regions of the central part of Eurasian continent and Pacific near the west coast of North America had main contribution to global average temperature warming trend stagnation in the last 10 years. And in southern hemisphere, Antarctic warming in middle troposphere was significant in recent years. Mid latitude regions existed weak cooling and low latitudes regions was warming affected by atmospheric in northern hemisphere. Atmosphere in upper troposphere and lower stratosphere had cooling trend in Antarctic early, but periphery of Antarctica region had independent temperature increasing, in recent 10 years, Antarctic warming range expanded rapidly, almost covered entire continent of Antarctica.After calculated nonlinear global upper air temperature instantaneous rate we found that, from 2003, troposphere over North and South Pacific showed rate negative region, and Cooling rate continued to accelerate, it was estimated that in the future, troposphere warming stagnation would continue for some time. The cooling in lower troposphere of northern hemisphere and the stratosphere over Pacific would not increase, and the cooling would intensify further in Arctic.Compared with traditional method, EEMD method can show more Temporal variation features of temperature trend, capture short time transition process of temperature trend provides great convenience for research of short-term climate change and climate variability.