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

JJA climatology ( average) precipitation (blue)[mm/day] Z500 anomaly from zonal mean (red line)[m] ∫(moisture flux) dp (vector)[kg/(ms)] 300hPa wind(vector)[m/s] 、 (blue line) PV grad. (shade)[ /(ms)] ○ Monsoon circulation, Baiu/Maiu ○ Double jet structure (contour levs=-20, 20) H L H

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

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

(1)Dominant pattern? 1 st mode of SVD for precipitation and Z500 over East Asia (1979~05 JJA) Grey lines: 95% significant level 1standard dev. scores of SVD1 Z500[m] Regression coefficient SVD1 explains 59% (SVD2 12% ) The Tripolar pattern is a dominant pattern precipitation[mm/day] Correlation with precipitation of the black box correlation: NINO 0.51, SST of Indian Ocean 0.66 The tripolar pattern is also a 1 st 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] Anyway the tripolar pattern appears 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?

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 location of the forcing heating moisture sink vorticity forcing [K/day] [10 -8 kg/(kg ･ s)] [ /s 2 ] (cf. Jin and Hoskins, 1995; Yasutomi 2003)

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

(2) What are the internal processes

(2) The internal processes? (Rossby waves, energy conversion, moist porcess) 850hPa climatology (avr of ) at the lower trop. (Yasutomi, 2003; Kosaka and Nakamura, 2006) Energy conversion (shade) WAF (Takaya and Nakamura, 2001) Energy→ strengthen amplitude waves→ relate south-north anomalies 1 st mode of SVD/EOF hPa (Obs.) Obs.

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

Conclusion (1)The tripolar pattern can be considered a dominant pattern of EASM climate variations (2)The tripolar pattern is determined the internal processes (a) energy conversion (b) moist processes (c) Rossby waves → relate each of south-north anomalies →An Internal mode of EASM Structure of climatological field: (a)The monsoon southwesterly at the lower troposphere. (b)Structure of the subpolar jet and subtropical jet. (c)The abundant moisture of the low-mid latitudes. maintain & strengthen anomalies