Jae-Heung Park, Soon-Il An

1.Introduction 2.Data 3.Result 4. Discussion 5. Summary

 Recently, as global warming continues, NPGO/NPO frequently appears compared to the past. This result is corresponding to the tropical climate change such as frequent generation of CP El Nino and temperature increase in Warm Pool. Since atmosphere leads oceans in the North Pacific, NPO becomes more important. (Yeh et al, 20011; Di Lorenzo et al 2010; Park et al, 2012; Furtado et al, 2011)  However, contrary to the study of AL, that of NPO or other atmosphere pattern is not arranged well. They are needed to be focused more.  In the North Pacific 1 st mode :: Pacific Decadal Oscillation (PDO) Aleutian Low (AL) 2 nd mode :: North Pacific Gyre Oscillation (NPGO) North Pacific Oscillation (NPO)

 Previous studies Wallace and Gutzler (1981) :: WPO (GPH 500hPa) & NPO (PSL) Nigam (2003) :: WPO & Asian-Pacific Jet (whole range of Pacific) Linkin and Nigam (2007) :: NPO & WPO.  In this study, we investigate the relationship between East Asia jet stream and atmosphere pressure over the North Pacific. It is suggested that this relationship can be connected to the Tropics.

:: NCEP-R1 reanalysis data (1949~2007, 708montly data  DJF mean 58 yearly data) :: Used variable - Zonal wind (U) - Geopotential Height (GPH) - Sea Level Pressure (SLP) - Omega - Temperature

 East Asia Jet (EA Jet) 1.East Asian Jet stream (> 70m/s) 2. Parallel to the latitude 3.Upstream region of North Pacific  EA Jet Axis Index EA Jet region ( E, 25-45N) :: It indicates the north-south movement of EA jet 1.Find latitudes where the strongest U exists at each longitude within EA jet region 2.Average the latitudes

 Composite Analysis :: zonal wind (200hPa) is composited with respect to the highest and lowest 10% of EA Jet axis index 1.When EA jet is located at north (south). zonal wind is strong (weak) 2.Shapes of jet in both period are similar in EA jet region, however, they are different in jet exit region. :: when EA jet locates at north(south), jet axis over the eastern North Pacific is toward northward(southward).  It implies that small difference of north-south displacement of EA jet is associated to the large change in atmosphere flow over the North Pacific. Solid – EA jet axis index (mean=32.5°N, std. 0.53) Dotted – 9-year running mean of the index increasing trend(95% significant level)  EA jet is moving northward.

 Regression Analysis :: EA Jet axis index is regressed onto the GPH(200hPa) & SLP. 1. Dipole pattern. (Northwest-low, Southeast-high) Similarity to NPO (scorr.=0.63) 2. Equivalent barotropic structure. 3. Simple regression relationship (SLPa) If EA jet axis moves northward by 3° 7.5hPa (250Pa x 3) increase and decrease at each center. :: Shading (95% significant level) Statistically apparent relationship between EA jet location and dipole pressure pattern over the North Pacific. :: This result indicates EA jet location plays an important role in making dipole structure.  What controls EA jet displacement??

 Relationship between EA Jet & Hadley Circulation :: Subtropical jet is located at the inner section of Hadley circulation boundary. :: At the boundary, tropopause height decreases abruptly. jet :: Using this information, Hadley circulation boundary (HCB) index is made. (local Hadley circulation, E, same to longitudinal range of EA jet region) :: The correlation between EA jet axis index and HCB index is 0.79 (95%) (closely linked)  Hadley circulation controls the location of EA jet.

 Correlation Map :: HCB index is correlated to Omega(500hPa) and Surface Air Temperature(SAT). 1. The correlation center is located in the western tropical Pacific. 2. Minus omega indicates upward motion or convection. If SAT is high and convection is strong in the region, then HCB moves northward. (EA jet moves to the north accordingly.) 3. Convection in the western tropical Pacific is an upward branch of Hadley and Walker circulations. The strong convection in the western tropical Pacific  strong Hadley and Walker circulations  cold sat & Northward movement ITCZ over the eastern Pacific 4. Omega index ( E, 0-20N)

1. Dipole structure (Northwest-Southeast axis) 2. Similar to the regression pattern.  Convection in the western tropical Pacific can affect the pressure over north Pacific via EA jet movement.  Composite Analysis :: SLP composite based on Omega index (above 1.5 std. – below -1.5 std.) solid :: Omega index dotted :: 9-year running mean of the index decreasing trend, 95%  Convection gets stronger in the western tropical Pacific.

Warming Convection↑ Cooling ITCZ↑ L H As global warming,  SST and convection in the western tropical Pacific increase.  The convection is upward branch of Hadley & Walker circulation, 1. Hadley circulation boundary moves northward. (EA jet) 2. Walker circulation gets stronger so that SST in eastern tropical Pacific cools.  ITCZ over the eastern tropical Pacific moves northward, and corresponding meridional circulation moves northward as well.  Jet stream over the whole pacific changes its axis, and secondary circulation induces low pressure at north and high pressure at south.