ヤマセに関する2-3の話題
1. 高解像度海上風と東北・北海道沿岸域波浪
2. 親潮とヤマセ時の海流変動
3. その他(時間があれば)
川村 宏
東北大学大学院理学研究科
1
Case Study of Wind Jet Transition and Localized
Responses of Wind Wave along the Pacific Coast of
Northern Japan by Synergetic Use of Satellite and In
Situ Observations
Shimada and Kawamura, J.Oceanogr., 63, pp. 953 to
966, 2007
キーワード:
散乱計海上風、海上ジェット気流、地形効果、太平洋沿岸域
ヤマセ海上風(Takai et al., 2006)
研究海域と気象・波浪観測点
波浪
計
AMeD
AS
2003年6月7-11日海上風場(SeaWinds on board Quickscats + ADEOSII)
移動
性高
気圧
高度
計
波浪
計測
充分に発達した二つの海上風ジェットの例
襟裳岬海上風ジェット
宮古沖海上風ジェット
日変動が顕著
海上風エネルギー(WE)と海面高度計波高分布(SWH)
襟裳崎
ジェット
(e)
南風の
場合(p)
多分、
うねり
(?)
沿岸域観測点の波高・波向と海上風速
襟裳崎ジェット
むつ小川原、八戸、久慈、釜石
宮古沖
ジェット
波の影
響は久
慈まで
2003年4-8月の襟裳観測点(a)と
三陸沖海上(b)の風ベクトル時系列
襟裳観測点
襟裳崎
ジェット
三陸沖海上
総じて東向き、宮古沖ジェットも
長期風向頻度分布と海上風場(本研究)
襟裳崎観測点(10年)
三陸沖(6年)
Seasonal to interannual variations of the western
AVHRR
Oyashio
SST
boundary
current
of
the
subarctic
North
Pacific
T/P
Intrusion
image
altimeter using altimeter data
SSH
Osamu Isoguchi and ○Hiroshi Kawamura
(JAXA/EORC)
(Tohoku University)
Covariance between the
time
series
the firstand T. Kono (1997): A study on wind-driven circulation in
Isoguchi,
O., H.of
Kawamura
the of
subarctic
North Pacific using TOPEX/POSEIDON altimeter data, J. Geophys.
EOF
the SLA
Res., 102, 12457-12468. Master thesis
(Sveldrup
transport) and
Isoguchi, O. and H. Kawamura (2003): Eddies advected by time-dependent Sverdrup
thecirculation
cross-track
in thevelocities
western boundary of the subarctic North Pacific, Geophysical
Research Letters, 30, doi:10.1029/2003GL017652. A part of Ph.D thesis
Isoguchi, O. and H. Kawamura (2006): Seasonal to interannual variations of the western
磯口治,
川村宏, 河野時廣, 川崎康寛(1995): 海面高度計と海洋観測データを用い
JGR
(1997)
boundary current of the subarctic North Pacific by a combination of the altimeter
た北海道南沖合域の海況変動,
海の研究,
163-174.
and tide gauge sea levels, J. Geophys.
Res., 111, 4,
C04013.
Isoguchi,
O.,and
H. Kawamura,
KonoOyashio
and Y. Kawasaki
(1995): Oceanic
Isoguchi, O.,
H. KawamuraT.(2006),
seasonal intensification
and itsvariations
effect on
observed
bytemperature
combining variation
altimeteroff
and
Umi-nosubsurface
thehydrographic
Sanriku coast, observations,
J. Geophys. Res.,
111,
Kenkyu,
163-174. Bachelar thesis
C10006, Vol.4,
doi:10.1029/2006JC003628.
12
2010/10/29 PICES 2010 @ Portland
Introduction
Previous works about Oyahio/East Kamchatka Current variations
Interannual variation
Southward shift of Oyashio water (subsurface
temperature field) shows a good correlation with
wintertime atmospheric forcing (Aleutian low and
related Sverdrup transport) (Sekine 1988;
Hanawa1995)
Seasonal variation
Hydrographic and moored buoy observations: strong
(weak) current/transport in winter/spring (summer/fall)
Present study
We demonstrate that altimeter and tide gauge sea levels are good indices of Oyashio/EKC
variations, which could connect dynamically the relationship between atmospheric forcing and
subsurface temperature fields in the previous studies.
We investigate in detail seasonal/intraseasonal evolution of Oyashio current and its effect on
sea surface/subsurface temperature fields off the Sanriku coast of Japan using derived indices.
13

Indices of Oyashio/EKC variations
Altimeter-derived Eddy Drifting Velocity (EDV)
and Geostrophic Current Anomaly (GCA)
Tide gauge sea levels

Seasonal/intraseasonal variation
 Interannual variation

14
Indices of Oyahio/EKC variations
Trajectories of eddies
Comparison
between eddies
propagating
velocity and
Sverdrup transport
Movement of eddies over Japan Trench and Kuril-Kamchatka Trench
could be a good index of Oyashio and EKC short term variation 15
[Isoguchi and Kawamura ,2006]
1) Eddy Drifting Velocity (EDV)
Along-trench distance (x-axis)-time (y-axis)
plot of normalized SLAs
Sea Level Anomaly
-Maps of SLA provided by AVISO
-Merged data from Jason1,Envisat,Topex/Poseidon,GFO
- time: Oct 1992 – Aug 2010
- 1/3 deg gridded SLAs every 7 day
EDV= Δx/ Δt
Δx: Lag distance in which cross-correlation
has a maximum
Δt: temporal distance of SLAs
16
Japan
Trench
Kuril-Kamchatka Trench
3) Tide sea levels at Petropavlovsk-Kamchatsky (PK-Tide)
Why Tide-PK ?
SLA EOF Mode 3(9.4%)
Petropavlovsk
-Kamchatsky (PK)
SLA EOF3
0.65
Sv(40N-50N)
0.57
0.69
Tide at PK
PK Tide is representative of sea level gradients across the KK Trench which is
related to large scale Sverdrup circulation.

Indices of Oyashio/EKC variations
Altimeter-derived Eddy Drifting Velocity (EDV)
and Geostrophic Current Anomaly (GCA)
Tide gauge sea levels

Seasonal/intraseasonal variation
 Interannual variation

18
Tide-PK
Annual cycles of
Tide-PK , Sv, EDV
PSMSL
1957/7-2002/12(45.5 years )
Removal of thermal steric
Sverdrup (40-50N)
NCEP/NCAR reanalyses
1957/7-2002/12(45.5 years)
Eddy drifting velocity
1992/10-2003/9(11years)
 Wintertime abrupt intensification (from minimum in late19fall to
max in winter)
 Secondary peak in early summer (in June)
Wintertime abrupt intensification
Climatology of Wind & Wind stress curl (October-March)
Oct
Jan
Nov
Feb
Dec
Mar
Westerlies rapidly shift southward from late fall to winter.
20
Wintertime abrupt intensification
Annual cycles of zonal
mean wind stress curl
based on NCEP 5-day
climatology
Annual cycles of areaaveraged (160E-140W,
40-50N) curl
Abrupt intensification caused by rapid southward migration of
westerlies
2
Secondary peak in
early summer (June)
Climatology of zonal
mean wind stress curl
in summer
Area-averaged
(160E-140W, 40-50N)
curl
North Pacific Index(based on SLP: Trenberth and Hurrell, 1994) shows small peak in
June.
Barotropic response to intraseasonal atmospheric variation seems to induce 22
Oyashio variation.
Effect on subsurface
temperature off the Sanriku
coast (red square)
Seasonal variation
Annual cycle of subsurface (200m) temperature
- from SAGE (JMA,2001) from 1990 to 2000
Estimation of meridional velocity
(v) based on an assumption that
temperature (T) variation is
induced by meridional heat
advection;
T
T
 v
t
y
Wintertime abrupt intensification
Secondary peak in early summer
23
ヤマセと陸奥湾周辺地形
ヤマセ風
陸奥湾
仙台湾
東北地方沿岸域の
大気・海洋・陸相互作用
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