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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

区域气候变化监测与检测学术研讨会，哈尔滨. 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 Wu 3. 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

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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

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  1. 区域气候变化监测与检测学术研讨会，哈尔滨 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

  2. 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.

  3. BackgroundChoice of base period/mean annual cycle for calculating anomaly 30-yr mean annual cycle Differences between different base periods Qian et al. 2010AAS

  4. 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

  5. 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): • Warming trend/increasing atmospheric CO2 concentration (e.g.Thomson 1995) • 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 • Its annual cycle is dominant • Its warming rate is more rapid than global mean or NH mean temperature over the past 5 decades (Ren et al. 2005) • It has plenty of meteorological observations

  6. 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)

  7. Method H: high-frequency component (several days to months) A: annual cycle (quasi-annual) L: low-frequency component (longer than one year) An adaptive and temporally local data analysis method － EEMD(ensemble empirical mode decomposition, Wu and Huang 2009) Magenta: amplitude of annual cycle Qian, Fu, Wu, 2011JC

  8. 年循环分量的方差贡献 Annual cycle is the dominant component: 65%~95% Qian, Fu, Wu, 2011JC

  9. 年循环平均振幅的空间分布 EOF analysis to the raw amplitude of the annual cycle (unit: ℃) zonal pattern Qian, Fu, Wu, 2011JC

  10. Trend analysis and attribution Amplitude of annual cycle for China mean surface solar radiation (SSR) • 年循环振幅变化主要是由地表太阳辐射变化引起的 • 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 1961–2007 • a multi-decadal change: from decreasing to increasing DTR: diurnal temperature range a proxy for surface solar radiation solar flux is present only during daylight and the nighttime minimum temperature is mainly governed by the thermal radiative exchanges Qian, Fu, Wu, 2011JC

  11. summer minus winter Trends in summer and winter temperature in China • Seasonal temperature discrepancy cannot be explained exclusively by the enhanced greenhouse effect

  12. Annual Cycle We propose Qian, Fu, Wu, 2011JC

  13. annual mean Annual Cycle We propose 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

  14. 年循环变化对研究气候变率和变化的意义 Annual mean temperature for China Different anomaly (deseasonalization) schemes • 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. TA: departure from mean annual cycle MA: departure from time-varying annual cycle Qian, Fu, Wu, 2011JC

  15. 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.

  16. QianYun et al. 2007GRL aerosol single scattering albedo (SSA)-less absobtion 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) 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).

  17. Changes in DTR (SSR)

  18. 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)

  19. Bypass this dilemma Qian et al. 2011JC

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