Why are there upwellings on the northern shelf of Taiwan under northeasterly winds? *. L.-Y. Oey [email protected] Outline : Introduction – upwelling, effects of strong currents A simple model of upwelling at the western edge of Kuroshio in East China Sea Observational evidences
Introduction – upwelling, effects of strong currents
A simple model of upwelling at the western edge of Kuroshio in East China Sea
*Chang, Oey, Wu & Lu, 2009 – J. Phys. Oceanogr. Submitted.
surface layer: 10~100m
Y:v/t + fu = y/z
fu = y/z
(..)dz fU = oy
U = under northeasterly winds?oy /f
oy < 0
oy > 0
Wind from north
Wind from south
U < 0
U= oy /f > 0
Trade Wind oy < 0
f > 0
f < 0
U= oy /f < 0
U= oy /f > 0
In the Presence of a Spatially Non-uniform Ocean Current under northeasterly winds?vo(x), the Ekman transport
U = oy /f ~ Period,
where f = fo+ o; o = vo/x
NE Monsoon oy<0
Jupiter = 10 hrs/rotation
Mars = 24.6 hrs/rotation
For oy < 0
T/t = A eit
Consider Oscillatory Wind:
T/t is in phase with wind if A > 0;
T/t is 1800 out of phase with wind if A < 0.
Wind under northeasterly winds?
T/t ~ oy(t) [s/xT/f ]
T/t ~ oy(t) [To/x]
East China Sea
Rossby number (Ro)
Southward wind: oy<0
Effects of Kuroshio: Long-Tung SST & wind stress under northeasterly winds?
Southward wind: cooling
T/t ~ oy(t)/(fE)[To/x +s/xT/f ]
Annual (~30yrs) Mean Wind under northeasterly winds?
Summary under northeasterly winds?
Current shears near strong ocean jets play a significant role in controlling the vertical motions in the ocean.
Generalizations under northeasterly winds?
(fh1/d)/t + voxxu = (f+vox)wE/d (1)
In SS, using wE = oy/(f +vox)2.voxx, (2)
we have, u = - oy/[d(f +vox)]. (3)
A “bulge” is defined as a near-surface buoyant fluid that moves across shelf as a result of Ekman transport by downwelling wind and its interaction with ocean’s vorticity across, say, a front. It is “2d-like” when |/y| << |/x| where y = alongshore and x = cross-shore. Idealized Calc.:
oy < 0
Caption: V-contours (black:0.2, 0.4, ..; grey: -0.05; white:-0.1,-0.15,-0.2,..) m/s, on color T (oC) from day 1 through 4after an up-front wind is applied.
A Nonlinear Model that moves across shelf as a result of Ekman transport by downwelling wind and its interaction with ocean’s vorticity across, say, a front. It is “2d-like” when |
Assume /H << 1, |/ y| << |/ x|;
Within the bulge, temperature T = Tb(x,z,t) is weakly stratified:
Tb = T- + (z + ), for 0z(x,t); g/N2 << 1 (A.1)
T- is related to the temperature Ti(z)beneath the bulge:
T- = Ti(), and Ti(z) = Tdeep + [N2/(g)](z + zdeep), for (x,t) z zdeep (A.2a,b)
Figure A2. The bulge solution according to equation (A.21) for C1 = 1 and various indicated values of c. Both the ordinate and abscissa are non-dimensionalized: ordinate is the bulge thickness (“”) below the free surface while the abscissa is = -1(xcnt); see text. For each c, the dotted line indicates where the solution terminates at the head of the bulge where a front is formed.
PV that moves across shelf as a result of Ekman transport by downwelling wind and its interaction with ocean’s vorticity across, say, a front. It is “2d-like” when | at day 80