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)
Slide 4
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.
Slide 5
:: 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
Slide 6
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 (120-160E, 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
Slide 7
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=32.5N, std. 0.53) Dotted 9-year running mean of the
index increasing trend(95% significant level) EA jet is moving
northward.
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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??
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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, 120-160E, 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.
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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 (100-145E, 0-20N)
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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.
Slide 12
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.