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Is Climate Change in Asia-Pacific Attributed to Human Activities?

Is Climate Change in Asia-Pacific Attributed to Human Activities?. Chang-Hoi Ho School of Earth and Environmental Sciences Seoul National University. Acknowledgments. Main collaborators

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Is Climate Change in Asia-Pacific Attributed to Human Activities?

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  1. Is Climate Change in Asia-Pacific Attributed to Human Activities? Chang-Hoi Ho School of Earth and Environmental Sciences Seoul National University

  2. Acknowledgments • Main collaborators • Climate Physical Laboratory, Seoul National University, Korea: Drs. Y.-S. Choi, J.-H. Kim, J.-H. Jeong- Website: http://cpl.snu.ac.kr • Bejing Normal University, China: Prof. D.-Y. Gong • National Central University, Taiwan: Prof. C.-H. Sui • Ewha Womans University, Korea: Prof. Seon-Ki Park • University of California, Los Angeles, USA: Dr. J. Kim • Seoul National University, Korea: Prof. R. J. Park

  3. Changes in the rainfall distribution of Korea Ho, C.-H., J.-Y. Lee, M.-H Ahn, and H.-S. Lee, 2003: A sudden change in summer rainfall characteristics in Korea during the late-1970s. International Journal of Climatology, 23, 117−128.

  4. 5-year average precipitation and number of rainy days during summer for rain rate  1 mm day-1 (a) and rain rate  30 mm day-1 (b). Solid line indicates the number of rainy days and bar represents the summer total precipitation.

  5. Daily precipitation contributed by typhoon Kim, J.-H., C.-H. Ho, M.-H. Lee, J.-H. Jeong, and D. Chen, 2006: Large increase in heavy rainfall associated with tropical cyclone landfalls in Korea after the late 1970s. Geophysical Research Letters, 33, L18706, doi:10.1029/2006GL027430.

  6. Long-term change in summer rainfall (Cases for  30 mm/day) (Cases for  0.1 mm/day) Ho, C.-H., J.-H. Kim, K.-M. Lau, K.-M. Kim, D.-Y. Gong, and Y.-B. Lee, 2005: Interdecadal changes in heavy rainfall in China during the northern summer. The Journal of Terrestrial, Atmospheric and Oceanic Sciences, 16, 1163−1176.

  7. 5870 gpm contour lines for each summer Gong, D.-Y. and C.-H. Ho, 2002: Shift in the summer rainfall over the Yangtze river valley in the late 1970s, Geophysical Research Letters, 29, 78.

  8. Interdecadal variability of TC tracks Increase decrease Increase decrease Recent summer-mean 500-hPa 5870m gpm Previous one Ho, C.-H., J.-J. Baik, J.-H. Kim, D.-Y. Gong, and C.-H. Sui, 2004: Interdecadal changes in summertime typhoon tracks. Journal of Climate, 17, 1767−1776.

  9. Summary • A number of our findings indicate the presence of considerable changes in summertime rainfall, typhoon, and large-scale circulation over East Asia. • However, the periods of the data are limited to the past few decades. Thus it remains insoluble whether these changes are due to climate change or climate variation. • Is there any decisive evidence showing that human activities alter the climate system?

  10. Some studies on rain-aerosol relation over China Choi, Y.-S., C.-H. Ho, D.-Y. Gong, R. J. Park, and J. Kim, 2007, The Impact of Aerosols on the Summer Rainfall Frequency in China, Journal of Applied Meteorology and Climatology (in press).

  11. Long-term trend of the rainfall event in summerand the increase in air pollution Southern China (from Cheng et al. 2005) Long-term trend of the number of rainfall event (in days/10-yr) in summer for 1955−1979 (upper) and 1980−2005 (lower). The red (blue) circle indicates positive (negative) value. Stations significant at the 90% level are indicated by filled circles. In contrast to the situation before 1979, the number of rainfall event has rapidly decreased since 1980.

  12. Different aerosol effects on precipitation Semi-direct Effect BC aerosols heat up the low-level atmosphere, and stabilize it Burn cloud droplets by UV absorption 1) suppress warm precipitation Indirect Effect Increase cloud droplets OH Reduce cloud droplet size SO2 +  H2SO4  Brighter Cloud 2)increase cloud lifetime,suppress warm precipitation 3) more aerosols and moisture are allowed to reach higher altitudes by updrafts, more cold precipitation from intense convective storms

  13. The increase in aerosol concentrations in China, via aerosol indirect and semi-direct effects, may affectthe long-term variations in precipitation Southern China (Cheng et al. 2005 JC) Eastern-central China (Zhao et al. 2006 GRL)

  14. The long-term trend of precipitation and aerosoland scientific question Question Increased aerosol reduced precipitation (Zhao et al. 2006 GRL) Or Less precipitation more aerosol in the air

  15. Employed surface PM10 observations • Air pollution Index (API) data • Period: June 5, 2000 to July 31, 2006 (summers only) • Available online at http://www.sepa.gov.cn/quality/air.php3 PM10 and precipitation station Beijing Chengdu Shanghai Guangzhou PM10 station

  16. Aerosol-precipitation interaction The significant correlation suggests that the increase in aerosol concentrationincreases rainfall frequency, which in turn removes aerosols from the atmosphere. This process is referred to “aerosol self-cleansing effect”.

  17. Relation with MODIS cloud properties a b c d e f

  18. Rainfall intensity-aerosol relationship Difference of the rain-day frequencies in terms of rainfall intensity in between the cases of high (100190 g m3) and low aerosol concentrations (090 g m3). A positive anomaly indicates that the frequency associated with the high aerosol cases dominates that associated with the low aerosol concentration. The error bar corresponds to the standard error of the anomaly. Bars significant at the 90% levels are indicated by red and blue colors.

  19. The possible role of aerosols in precipitation 7 6 5 4 3 2 1 IN CCN SEEDERZONE Height (km) Cold-rain process enhances moderate rain FEEDERZONE Warm-rain process suppresses light rain Additional moisture & aerosols

  20. The self-cleansing system of aerosols Ice cloud Formation Increase Increase A self-cleansing system Air pollutants Rain frequency Wet scavenging

  21. Contradictory long-term trend in rainfall event Rainfall event (in days/10-yr) 19501979 19802006 -1.3 Despite the aerosol self-cleansing effect, aerosol concentration has been increasing in China, accompanied by a decrease in rainfall events, over the last few decades. < 6 6 ~ 3 3 ~ 0 0 ~ 3 3 ~ 6  6 -2.8

  22. Long-term trends in RH and SH 19501979 Relative humidity (in %/10-yr), NCEP Relative humidity (in %/10-yr), observation 19802006 19802006 Specific humidity (in g/10-yr), observation 19802006

  23. Detrainmental effect of human activities on the nature over East Asia Local sources of aerosoldue to industrialization Regional climate variationson decadal time scale An increase in aerosols A decrease in rain frequency Aerosol self-cleansing system An increase in rain frequencydue to cloud ice nuclei Aerosols Rain frequency An increase in wet scavenging due to a increase in rain frequency A decrease in wet scavenging due to a decrease in rain frequency

  24. Summary • The aerosol self-cleansing effect is another important mechanism involved in aerosol-cloud-rainfall interaction in the summertime in China. • Despite the presence of aerosol self-cleansing effect, aerosol concentration has been increasing in China, accompanied by a decrease in rainfall events, over the last few decades. • These results show that the impact of reduced RH dominates the aerosol self-cleansing mechanism in determining the long-term trend in rainfall frequency, and additionally contributing to the increase in aerosol concentrations since the beginning of the industrialization of China in 1980s.

  25. A weekly cycle of aerosol-meteorology interaction over China Gong, D.-Y., G. Dong, and C.-H. Ho, 2006: Weekend effect in diurnal temperature range in China: Opposite signals between winter and summer. Journal of Geophysical Research, 111, D18113. Gong, D.-Y., C.-H. Ho, D. Chen, Y. Qian, Y.-S. Choi, and J. Kim, 2007: A weekly cycle of aerosol-meteorology interaction over China. Journal of Geophysical Research, 112, D22202. Choi, Y.-S., C.-H. Ho, D. Chen, Y.-H. Noh, and C.-K. Song, 2007, Spectral analysis of weekly variation in PM10 mass concentration and environment conditions over China, Atmospheric Environment (in press).

  26. Weekly cycle of aerosol-meteorology interaction • Scientists began to pay attention to find more clear evidence of anthropogenic effect. • Weekly cycle of aerosol and meteorology is only a clear evidence of anthropogenic effect on the nature. • Satellite-observed gas/aerosol (Delene and Ogren 2002; Beirle et al. 2003) • Surface-observed gas/aerosol: carbon oxide (Hies et al. 2000; Cerveny and Coakley 2002), nitrogen oxide (Marr and Harley 2002), and PM (Jin et al. 2005; Gong et al. 2007) • DTR (Forster and Solomon 2003; Gong et al. 2006) • Cloud and precipitation (Cerveny and Balling Jr. 1998; Jin et al. 2005)

  27. Evidences of weekly cycles in urban region Jin et al. (2005), Urban aerosols and their variations with clouds and rainfall: A case study for New York and Houston, JGR Cerveny and Balling (1998), Weekly cycles ofair pollutants, precipitation and tropical cyclones in the coastal NW Atlantic region, Nature 1946-96 1970-96

  28. Evidences of weekly cycles in the globe weekend-weekday Weekend effect for stations outside the U.S., using 1980–1999 data. Filled circles are temporally significant at the 95% confidence level. The diameter of the circle is related to the size of the DTR weekend effect in Kelvin (Forster and Solomon, 2003 PNAS).

  29. Scientific question • Why do aerosol concentrations show a maximum on Wednesday or Thursday in China?

  30. Relation with low-level wind field

  31. Relation with temperature profile

  32. Relation with DTR and rain frequency

  33. Summary • The PM10 (aerosol particulate matters of diameter < 10 m) concentrations in China show significant weekly cycles with the largest values around midweek and smallest values in weekend. • Accompanying this weekly PM10 cycle, the meteorological variables such as wind speed, air temperature, show notable and consistent weekly cycles. • We hypothesize that the changes in the atmospheric circulation may be triggered by the accumulation of PM10 through diabatic heating of the lower troposphere.

  34. Concluding Remarks • The impact of aerosols on the regional hydroclimate, as a part of anthropogenic effects together with greenhouse gases, involves a number of processes on a wide range of time scales • Aerosol-cloud interaction (hourly or shorter) • Aerosol-accumulation-rainfall and wet scavenging (a few days) • Aerosol-meteorology interaction (weekly) • Long-term variations in the atmospheric RH modulate the formal effects (decadal or longer) • We believe that these processes are going on, and will be clearer, at least over East Asia, in the future.

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