共查询到20条相似文献，搜索用时 46 毫秒
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The signatures of mesoscale eddies induced surface and subsurface changes have not been comprehensively quantified for the Bay of Bengal (BoB) region. This study quantifies the statistical properties and three-dimensional (3D) eddy structures in the BoB. To accomplish this, the satellite altimetry data combined with automated eddy detection and tracking algorithm is used. Horizontal distribution of surface characteristics of eddies is analyzed by using 24 years (1993–2016) of AVHRR infrared satellite sea surface temperature (SST) and 7 years (2010–2016) of sea surface salinity (SSS) of SMOS satellite data. Surface eddy centric composite analysis reveals the existence of warm (cold) and diverse SSS anomalies for anticyclonic (cyclonic) eddies. During winter, it is important to note that the eddy induced SST and SSS anomalies show the dipole patterns show opposite phases for the cyclonic and anticyclonic eddies. Observed diploe structures are consistent with the eddy rotation and background large-scale meridional gradient of temperature and salinity fields. The 3D structure of eddies is investigated by using the ARMOR3D and Argo float profiles. The horizontal distribution of temperature and salinity anomalies from ARMOR3D signify the monopole structure of eddies in the subsurface layers. Further, the analysis of composite averages of 241 (200) Argo temperature profiles indicates the core of anticyclonic (cyclonic) eddies centered at about ∼140 m (∼100 m). However, salinity profiles depict the existence of core at ∼65 m (∼50 m). This study have practical relevance to a variety of stakeholders and finds profound importance in the validation of eddy-resolving ocean models for the BoB region. 相似文献
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M. G. Giometto R. Grandi J. Fang P. A. Monkewitz M. B. Parlange 《Boundary-Layer Meteorology》2017,162(2):307-317
The Nieuwstadt closed-form solution for the stationary Ekman layer is generalized for katabatic flows within the conceptual framework of the Prandtl model. The proposed solution is valid for spatially-varying eddy viscosity and diffusivity (O’Brien type) and constant Prandtl number (Pr). Variations in the velocity and buoyancy profiles are discussed as a function of the dimensionless model parameters \(z_0 \equiv \hat{z}_0 \hat{N}^2 Pr \sin {(\alpha )} |\hat{b}_\mathrm{s} |^{-1}\) and \(\lambda \equiv \hat{u}_{\mathrm{ref}}\hat{N} \sqrt{Pr} |\hat{b}_\mathrm{s} |^{-1}\), where \(\hat{z}_0\) is the hydrodynamic roughness length, \(\hat{N}\) is the Brunt-Väisälä frequency, \(\alpha \) is the surface sloping angle, \(\hat{b}_\mathrm{s}\) is the imposed surface buoyancy, and \(\hat{u}_{\mathrm{ref}}\) is a reference velocity scale used to define eddy diffusivities. Velocity and buoyancy profiles show significant variations in both phase and amplitude of extrema with respect to the classic constant \(\textit{K}\) model and with respect to a recent approximate analytic solution based on the Wentzel-Kramers-Brillouin theory. Near-wall regions are characterized by relatively stronger surface momentum and buoyancy gradients, whose magnitude is proportional to \(z_0\) and to \(\lambda \). In addition, slope-parallel momentum and buoyancy fluxes are reduced, the low-level jet is further displaced toward the wall, and its peak velocity depends on both \(z_0\) and \(\lambda \). 相似文献
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Data from the Antarctic winter at Halley Base have been used in order to evaluate qualitatively and quantitatively how the stratification in the low atmosphere (evaluated with the gradient Richardson number, Ri) influences the eddy transfers of heat and momentum. Vertical profiles of wind and temperature up to 32 m, and turbulent fluxes (
,
and
) measured from three ultrasonic thermo-anemometers installed at 5, 17 and 32 m are employed to calculate Ri, the friction velocity (u
*) and the eddy diffusivities for heat (K
h
) and momentum (K
m
). The results show a big dependence of stability onK
m
,K
h
andu
*, with a sharp decrease of these turbulent parameters with increasing stability. The ratio of eddy diffusivities (K
h
/K
m
) is also analyzed and presents a decreasing tendency as Ri increases, reaching values even less than 1, i.e., there were situations where the turbulent transfer of momentum was greater than that of heat. Possible mechanisms of turbulent mixing are discussed. 相似文献
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Comparisons between sensible heat flux measured using eddy correlation instrumentation and estimated using the temperature fluctuation method are presented for four types of surface in West Africa. Agreement between measured and estimated values is good. Regression of estimated on measured sensible heat flux gave a mean slope of 0.98 with a mean r
2 of 0.94 for bare soil, mature millet, fallow savannah and tiger bush. Estimates of heat flux from temperature fluctuations measured by an instrument mounted beneath a tethered balloon are also shown to be in close agreement with eddy correlation measurements made at the surface (regression slope = 0.98, r
2 = 0.84). The results provide evidence that the ratio /×is indeed a universal function of z/L for all the surface types considered. 相似文献
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A two-dimensional mesoscale model has been developed to simulate the air flow over the Gulf Stream area where typically large gradients in surface temperature exist in the winter. Numerical simulations show that the magnitude and the maximum height of the mesoscale circulation that develops downwind of the Gulf Stream depends on both the initial geostrophic wind and the large-scale moisture. As expected, a highly convective Planetary Boundary Layer (PBL) develops over this area and it was found that the Gulf Stream plays an important role in generating the strong upward heat fluxes causing a farther seaward penetration as cold air advection takes place. Numerical results agree well with the observed surface fluxes of momentum and heat and the mesoscale variation of vertical velocities obtained using Doppler Radars for a typical cold air outbreak. Precipitation pattern predicted by the numerical model is also in agreement with the observations during the Genesis of Atlantic Lows Experiment (GALE).List of Symbols
u
east-west velocity [m s–1]
-
v
north-south velocity [m s–1]
-
vertical velocity in coordinate [m s–1]
-
w
vertical velocity inz coordinate [m s–1]
- gq
potential temperature [K]
-
q
moisture [kg kg–1]
-
scaled pressure [J kg–1 K–1]
-
U
g
the east-south component of geostrophic wind [m s–1]
-
V
g
the north-south component of geostrophic wind [m s–1]
-
vertical coordinate following terrain
-
x
east-west spatial coordinate [m]
-
y
north-south spatial coordinate [m]
-
z
vertical spatial coordinate [m]
-
t
time coordinate [s]
-
g
gravity [m2 s–1]
-
E
terrain height [m]
-
H
total height considered in the model [m]
-
q
s
saturated moisture [kg kg–1]
-
p
pressure [mb]
-
p
00
reference pressure [mb]
-
P
precipitation [kg m–2]
-
vertical lapse rate for potential temperature [K km–1]
-
L
latent heat of condensation [J kg–1]
-
C
p
specific heat at constant pressure [J kg–1 K–1]
-
R
gas constant for dry air [J kg–1 K–1]
-
R
v
gas constant for water vapor [J kg–1 K–1]
-
f
Coriolis parameter (2 sin ) [s–1]
-
angular velocity of the earth [s–1]
-
latitude [o]
-
K
H
horizontal eddy exchange coefficient [m2 s–1]
- t
integration time interval [s]
- x
grid interval distance inx coordinate [m]
- y
grid interval distance iny coordinate [m]
-
adjustable coefficient inK
H
-
subgrid momentum flux [m2 s–2]
-
subgrid potential temperature flux [m K s–1]
-
subgrid moisture flux [m kg kg–1 s–1]
-
u
*
friction velocity [m s–1]
-
*
subgrid flux temperature [K]
-
q
*
subgrid flux moisture [kg kg–1]
-
w
*
subgrid convective velocity [m s–1]
-
z
0
surface roughness [m]
-
L
Monin stability length [m]
-
s
surface potential temperature [K]
-
k
von Karman's constant (0.4)
-
v
air kinematic viscosity coefficient [m2 s–1]
-
K
M
subgrid vertical eddy exchange coefficient for momentum [m2 s–1]
-
K
subgrid vertical eddy exchange coefficient for heat [m2 s–1]
-
K
q
subgrid vertical eddy exchange coefficient for moisture [m2 s–1]
-
z
i
the height of PBL [m]
-
h
s
the height of surface layer [m] 相似文献
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