1990年代初中国气温变化的年代际转折及与地表太阳辐射变化的可能联系

钱诚 1, 符淙斌 2,1, Zhaohua Wu3

1. 中国科学院东亚区域气候－环境重点实验室，中国科学院大气物理研究所2. 南京大学气候与全球变化研究院，南京大学大气科学学院

3. Department of Earth, Ocean and Atmospheric Science & Center for Ocean-Atmospheric Prediction Studies, Florida State University, Tallahassee, Florida, USA

区域气候变化监测与检测学术研讨会，哈尔滨

Background The annual cycle is the dominant component for many

climate variables outside the tropics and the most prominent climate oscillation.

However, to date only a limited number of analyses have been reported concerning its variability and changes, especially in the seasonality of surface air temperature (SAT), under a changing climate in contrast to the numerous studies focusing on long-term global or regional warming.

This is partly because the annual cycle of a climate variable, which is traditionally assumed repetitive from year to year and estimated by averaging the values of that variable for the same day/month over a period of several years, is frequently removed in studies concerning climate variability or changes.

BackgroundChoice of base period/mean annual cycle for calculating anomaly

Differences between different base periods

30-yr mean annual cycle

Qian et al. 2010AAS

Definition of El NiñoSensitive to the choice of base period/mean annual cycle

But the underlying physical process of past ENSO is already a reality Qian et al. 2011JC

Background Several observational analyses have reported that the amplitude

of the annual cycle of land SAT decreases (weakening seasonality) (e.g., Thomson 1995; Stine et al. 2009) in much of the Northern Hemisphere (NH) during global warming.

However, the causes and significance of these observed changes remain poorly understood (Stine et al. 2009):

① Warming trend/increasing atmospheric CO2 concentration (e.g.Thomson 1995)

② internal atmospheric variability, e.g. the North Atlantic Oscillation (e.g. Zveryaev 2007) or the northern annular mode (Stine et al. 2009).

China is one of the ideal countries for studying changes in the annual cycle and whether they are related to a warming tendency or to an increasing atmospheric CO2 concentration

① Its annual cycle is dominant② Its warming rate is more rapid than global mean or NH mean temperature

over the past 5 decades (Ren et al. 2005)③ It has plenty of meteorological observations

Data• an updated homogenized daily mean/maximum/minimum surface air

temperature dataset, which is based on 549 meteorological station observations in China for the period 1960–2008 (Li and Yan 2009)

• global mean near-surface temperature anomalies from 1961 to 2007 (Brohan et al. 2006)

• atmospheric CO2 concentration at Mauna Loa, Hawaii, from 1965 to 2007

• surface solar radiation (including direct radiation and diffuse radiation) averaged from 37 meteorological stations in China (only 37 of 122 stations have consecutive series from 1961 to 2007)

MethodAn adaptive and temporally local data analysis method－ EEMD (ensemble empirical mode decomposition, Wu and Huang 2009)

)()()()( tLtAtHtX H: high-frequency component (several days to months)A: annual cycle (quasi-annual)L: low-frequency component (longer than one year)

Magenta: amplitude of annual cycleQian, Fu, Wu, 2011JC

Annual cycle is the dominant component: 65%~95%

Qian, Fu, Wu, 2011JC

年循环分量的方差贡献

EOF analysis to the raw amplitude of the annual cycle (unit: ℃)

zonal patternQian, Fu, Wu, 2011JC

年循环平均振幅的空间分布

Trend analysis and attribution

• 年循环振幅变化主要是由地表太阳辐射变化引起的

Amplitude of annual cycle for China mean surface solar radiation (SSR)

Variation and change in the amplitude of the AC are notable:peak-to-peak variation: 13% of its mean amplitude or 1.8℃;a significant (P<0.01) decreasing by –4.6% or –0.63℃ for the period 1961–2007a multi-decadal change: from decreasing to increasing

DTR: diurnal temperature rangea proxy for surface solar radiation

Qian, Fu, Wu, 2011JC

solar flux is present only during daylight and the nighttime minimum temperature is mainly governed by the thermal radiative exchanges

Trends in summer and winter temperature in China

• Seasonal temperature discrepancy cannot be explained exclusively by the enhanced greenhouse effect

summer minus winter

We propose

Annual Cycle

Qian, Fu, Wu, 2011JC

We propose

Annual Cycle

annual mean

The combined effect of the global dimming/brightening transition and a gradual increase in greenhouse warming has led to the seasonal discrepancy and transition, and the accelerated warming after early 1990s

年循环变化对研究气候变率和变化的意义

• 如何计算气候距平 (considering either the conventional repetitive climatological annual cycle or the time-varying annual cycle) 会影响气候变化的趋势估计 .

Annual mean temperature for China Different anomaly (deseasonalization) schemes

TA: departure from mean annual cycleMA: departure from time-varying annual cycle

Qian, Fu, Wu, 2011JC

请批评指正 !

Reference:Qian C, C Fu, and Z. Wu, 2011: Changes in the amplitude of the temperature annual cycle in China and their implication for climate change research. J. Climate, In press, doi: 10.1175/JCLI-D-11-00006.1

Martin Wild (Personal communication):I read it with great interest. These are very nice and convincing results indeed.

Possible reasons for changes in SSR

• Possible reason for the overall decreasing trend of SSR is believed due mainly to changes in the transparency of atmosphere (Wild 2009)

• concurrent increasing trends in cloud-free sky over China (Qian et al. 2006)

• increasing emissions of anthropogenic aerosols resulted in less solar radiation reaching the ground (Che et al. 2005; Qian et al. 2006; Streets et al. 2006; Qian et al. 2007; Shi et al. 2008; Wild 2009)

aerosol single scattering albedo (SSA)-less absobtion

QianYun et al. 2007GRL

Qian, Fu, Wu, 2011JC

Wild (2009): the dimming/brightening transition in China may be related to changes in fuel utilization, and thus in aerosol composition and in associated single scattering albedo (Qian et al. 2007).

Changes in DTR (SSR)

EEMD to Niño-3 SST index (1881-2007)

57%

29%

Qian C, Z Wu, C Fu, and D Wang, 2011: On changing El Niño: A view from time-varying annual cycle, interannual variability and mean state. J. Climate, doi: 10.1175/JCLI-D-10-05012.1 (In press)

Bypass this dilemma

Qian et al. 2011JC