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Formation processes of tripolar climate anomaly over East Asia in summer

Formation processes of tripolar climate anomaly over East Asia in summer. Nagio Hirota and Masaaki Takahashi CCSR, University of Tokyo 2008/6/23. Previous studies about variability of EASM. Z500 associated with distinct / obscure Baiu (Tagami, 2005). Z500 related to NINO3.4 of DJF

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Formation processes of tripolar climate anomaly over East Asia in summer

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  1. Formation processes of tripolar climate anomaly over East Asia in summer Nagio Hirota and Masaaki Takahashi CCSR, University of Tokyo 2008/6/23

  2. Previous studies about variability of EASM Z500 associated with distinct / obscure Baiu (Tagami, 2005) Z500 related to NINO3.4 of DJF (Wang et al., 2001) Objective: Different types of forcing, but similar tripolar structure →why? 850hPa stream function associated with Indian Ocean SST of MAM (Endo, 2005) A response to doubled CO2 precipitation, Z500, 850 wind (Kimoto, 2005)

  3. (1) Is the tripolar pattern dominant pattern of EASM climate variability?

  4. (1)Dominant pattern? 1st mode of SVD for precipitation and Z500 over East Asia (1979~05 JJA) The tripolar pattern is also a 1st mode of other SVD & EOF anaysis： → EOF1 of Precipitation (13%) , EOF1 of Z500 (43%) → over the Norther Hemisphere (43%), over the globe (36%) → covariance matrix (SVD2, 27%) → June (46%), August(46%), interseasonal variations(19%) SVD1 over the NH Z500[m] SVD1 over the NH precipitation[mm/day] scores of SVD1 SVD1 explains 59% (SVD2 12%) Anyway the tripolar pattern appears The Tripolar pattern is a dominant pattern If climate variations are considered as atmospheric responses to external forcing, “different forcing” & “similar tripolar pattern” suggest importance of internal processes of atmosphere → Internal mode? 1standard dev. correlation: NINO 0.51, SST of Indian Ocean 0.66 Regression coefficient Z500[m] precipitation[mm/day] Correlation with precipitation of the black box 0.771 Grey lines: 95% significant level

  5. To show the importance of internal processes Model：a linear primitive model with moist process, T42L20 Experimental design (a) Calculate a number of linear responses to external forcing distributed uniformly over the Northern Hemisphere (b) Extract a dominant pattern from these responses by SVD analysis →the dominant pattern is determined by the internal processes [10-8kg/(kg･s)] [K/day] [10-10/s2] location of the forcing heating moisture sinkvorticity forcing (cf. Jin and Hoskins, 1995; Yasutomi 2003)

  6. …(206 responses)

  7. Result(SVD1; explaines 52%)→the tripolar pattern SVD1 of observation SVD scores Z500[m] A dominant pattern of responses to the forcing distributed uniformly. →Therefore, we speculate that disturbances in different regions trigger similar internal processes over East Asia, resulting in a similar tripolar pattern.

  8. (2) What are the internal processes

  9. Z500と850hPaのWAF Cooling Precip & moisture flux [m] a dry response [mm/day] (2) The internal processes? (Rossby waves, moist porcess, energy conversion) Example: A response to the forcing around Philippines Z500 & WAF at 850hPa Cooling a moist response

  10. Conclusion • The tripolar patterncan be considered a dominant patternof EASMclimate variations • The tripolar patternis determinedthe internal processes • (a) energy conversion • (b) moist processes • (c) Rossby waves →relate each of south-north anomalies • →An Internal mode of EASM maintain & strengthen anomalies • Structure of climatological field: • The monsoon southwesterlyat the lower troposphere. • Structure of the subpolar jetand subtropical jet. • The abundant moisture of the low-mid latitudes.

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