scholarly journals Wind Stress Dynamics in Chesapeake Bay: Spatiotemporal Variability and Wave Dependence in a Fetch-Limited Environment

2015 ◽  
Vol 45 (10) ◽  
pp. 2679-2696 ◽  
Author(s):  
Alexander W. Fisher ◽  
Lawrence P. Sanford ◽  
Steven E. Suttles
Keyword(s):  
Chesapeake Bay ◽  
Wind Stress ◽  
Wave Model ◽  
Heat Fluxes ◽  
Spatiotemporal Variability ◽  
Surface Heat Fluxes ◽  
Wave Measurements ◽  
Variable Surface ◽  
Ultrasonic Anemometer ◽  
Variable Wind

AbstractThe spatiotemporal variability of wind stress dynamics in Chesapeake Bay has been investigated using a combination of observations and numerical modeling. Direct measurements of momentum and surface heat fluxes were collected using an ultrasonic anemometer deployed on a fixed tower in the middle reaches of Chesapeake Bay in the spring of 2012 along with collocated wave measurements. These measurements were compared to bulk estimates of wind stress using wave-dependent formulations of the Charnock parameter (alpha). Results indicate that a constant alpha value of 0.018 reasonably represents observed stress values, but estimates can be improved by the inclusion of surface wave information in the parameterization of alpha. Using a wave age formulation of alpha in combination with an optimally interpolated 10-m neutral wind field, a third-generation numerical wave model, Simulating Waves Nearshore (SWAN), was employed to investigate the spatiotemporal variability of wind stress across the estuary. Alpha values were found to be wind speed dependent and displayed spatial distributions that ranged between open-ocean values and strongly fetch-limited values. Model results suggest that variable wind stress dynamics stemming from a combination of variable surface winds and fetch-limited wave growth may result in the 10-m neutral drag coefficient varying by a factor of 2 across the estuary. Up to 20% of these changes can be directly attributed to the effects of variable waves.

scholarly journals Oceanic Response to Surface Loading Effects Neglected in Volume-Conserving Models

2006 ◽  
Vol 36 (3) ◽  
pp. 426-434 ◽  
Author(s):  
Rui M. Ponte
Keyword(s):  
Time Scales ◽  
Deep Ocean ◽  
Heat Fluxes ◽  
Freshwater Flux ◽  
Surface Heat Fluxes ◽  
Sea Level Fluctuations ◽  
Freshwater Fluxes ◽  
Variable Surface ◽  
Loading Effects ◽  
Surface Loads

Abstract Forcing by freshwater fluxes implies variable surface loads that are not treated in volume-conserving ocean models. A similar problem exists with the representation of volume changes implied by surface heat fluxes. Under the assumption of an equilibrium response, such surface loads merely lead to spatially uniform sea level fluctuations, which carry no dynamical significance. A barotropic model forced by realistic freshwater fluxes is used to test the validity of the equilibrium assumption on seasonal to daily time scales. The simulated nonequilibrium signals have amplitudes much weaker than those of the forcing, with standard deviations well below 1 mm over most of the deep ocean. Larger values (up to ∼1 cm) can be found in shallow and semienclosed coastal areas, where the equilibrium assumption can lead to substantial errors even at monthly and longer time scales. Forcing by mean seasonal river runoff yields similar results, and heat flux effects lead to weaker nonequilibrium signals. In contrast, nonequilibrium signals driven by atmospheric pressure loading are at least an order of magnitude larger than those forced by freshwater fluxes. The exceptions occur for some shallow, coastal regions in the Tropics and at the longest time scales, in general, where forcing by freshwater flux is much stronger than by pressure.

Effects of Sea State and Small-Scale Currents on Air-Sea Fluxes in the Northwest Tropical Atlantic Ocean

2021 ◽  
Author(s):  
Cesar Sauvage ◽  
Hyodae Seo ◽  
Carol Anne Clayson ◽  
Jim Edson
Keyword(s):  
Wind Stress ◽  
Wave Model ◽  
Heat Fluxes ◽  
Ocean Currents ◽  
Small Scale ◽  
Turbulent Heat ◽  
Sea State ◽  
Trade Winds ◽  
Low Level ◽  
Directional Alignment

<p>The Northwest Tropical Atlantic is characterized by the strong North Brazilian Current (NBC), its rings, and numerous mesoscale eddies, which ceaselessly interact with the persistent trade winds and trade cumuli. Near the coast, the ocean stratification is maintained by the Amazon and Orinoco river discharges, which control the vertical mixing and the near-shore circulation dynamics. Breaking waves and swells are ubiquitous under the trade winds, and hence, the wave-induced mixing and wave-mediated air-sea fluxes are expected to modulate the eddy variability and low-level clouds. Our study aims to enhance understanding of the air-sea fluxes mediated by the mesoscale ocean currents and surface waves and evaluate their impacts on the ocean and atmosphere.</p><p>High-resolution ocean model (ROMS) and wave model (WW3) simulations are conducted for the period of the ATOMIC/EUREC4A experiments. The model surface state variables are used to compute offline the air-sea heat and momentum fluxes using the latest COARE v3.6 bulk flux algorithm under various sea state conditions induced by surface waves, ocean currents, and their interaction. The results demonstrate that considering the spatial variability in sea states via wave slope and wave age (e.g., swells and wind-seas) leads to enhanced spatial variability in drag coefficient and wind stress. Comparison to wind stress estimated using the wind-speed dependent formulation, meaning that COARE makes sea state assumptions under given wind, indicates that, at any given time, wind and wave in fact, rarely match those assumptions. The swells (wind-seas) decreases (increases) the sea surface roughness length, drag coefficient, and wind stress by 10-15%. However, we find that the sea state impact on turbulent heat flux is negligible.</p><p>More importantly, we also show that considering the ocean currents in the COARE algorithm yields much stronger spatio-temporal variations in not just the wind stress but also turbulent heat fluxes. The intense and small-scale current fields in this region are associated with the NBC and its rings, smaller mesoscale eddies, and filamentary density fronts associated with the freshwater plumes. The surface currents associated with these small-scale energetic features alter the relative wind speed and thus the air-sea fluxes depending on the directional alignment between the wind and current; the increase (decrease) in both the wind and heat fluxes by ~20% is found with the current and wind are in the opposite (same) direction wind. Moreover, this relative wind effect appears to be reinforced by wave direction as well, also via the directional alignment between waves and currents, since the waves are mainly aligned with the trade wind in this region.</p><p>Further analyses are underway to examining the seasonality of the modulation by the wave-current interaction, quantifying the role of the freshwater distribution, and exploring the time-mean influence on the low-level clouds. The results from the ocean and wave modeling efforts will guide our ongoing fully coupled ocean-atmosphere (and wave) model simulations to quantify their impacts on the atmosphere, including low-level clouds.</p>

Trends of land surface heat fluxes on the Tibetan Plateau from 2001 to 2012

2017 ◽  
Vol 37 (14) ◽  
pp. 4757-4767 ◽  
Author(s):  
Cunbo Han ◽  
Yaoming Ma ◽  
Xuelong Chen ◽  
Zhongbo Su
Keyword(s):  
Tibetan Plateau ◽  
Land Surface ◽  
Surface Heat ◽  
Heat Fluxes ◽  
The Tibetan Plateau ◽  
Surface Heat Fluxes ◽  
Land Surface Heat Fluxes

scholarly journals The West Coast Thermal Trough: Mesoscale Evolution and Sensitivity to Terrain and Surface Fluxes

2013 ◽  
Vol 141 (8) ◽  
pp. 2869-2896 ◽  
Author(s):  
Matthew C. Brewer ◽  
Clifford F. Mass ◽  
Brian E. Potter
Keyword(s):  
High Pressure ◽  
West Coast ◽  
Energy Equation ◽  
Potential Temperature ◽  
Wrf Model ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
The West ◽  
Surface Heat Fluxes ◽  
Thermodynamic Energy

Abstract Despite the significant impacts of the West Coast thermal trough (WCTT) on West Coast weather and climate, questions remain regarding its mesoscale structure, origin, and dynamics. Of particular interest is the relative importance of terrain forcing, advection, and surface heating on WCTT formation and evolution. To explore such questions, the 13–16 May 2007 WCTT event was examined using observations and simulations from the Weather Research and Forecasting (WRF) Model. An analysis of the thermodynamic energy equation for these simulations was completed, as well as sensitivity experiments in which terrain or surface fluxes were removed or modified. For the May 2007 event, vertical advection of potential temperature is the primary driver of local warming and WCTT formation west of the Cascades. The downslope flow that drives this warming is forced by easterly flow associated with high pressure over British Columbia, Canada. When the terrain is removed from the model, the WCTT does not form and high pressure builds over the northwest United States. When the WCTT forms on the east side of the Cascades, diabatic heating dominates over the other terms in the thermodynamic energy equation, with warm advection playing a small role. If surface heat fluxes are neglected, an area of low pressure remains east of the Cascades, though it is substantially attenuated.

On the Hyperbolicity of the Bulk Air–Sea Heat Flux Functions: Insights into the Efficiency of Air–Sea Moisture Disequilibrium for Tropical Cyclone Intensification

2021 ◽  
Vol 149 (5) ◽  
pp. 1517-1534
Author(s):  
Benjamin Jaimes de la Cruz ◽  
Lynn K. Shay ◽  
Joshua B. Wadler ◽  
Johna E. Rudzin
Keyword(s):  
Tropical Cyclone ◽  
Surface Wind ◽  
Heat Content ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Ocean Heat Uptake ◽  
Surface Heat Fluxes ◽  
Heat Uptake ◽  
Moisture Fluxes ◽  
New Perspective

AbstractSea-to-air heat fluxes are the energy source for tropical cyclone (TC) development and maintenance. In the bulk aerodynamic formulas, these fluxes are a function of surface wind speed U10 and air–sea temperature and moisture disequilibrium (ΔT and Δq, respectively). Although many studies have explained TC intensification through the mutual dependence between increasing U10 and increasing sea-to-air heat fluxes, recent studies have found that TC intensification can occur through deep convective vortex structures that obtain their local buoyancy from sea-to-air moisture fluxes, even under conditions of relatively low wind. Herein, a new perspective on the bulk aerodynamic formulas is introduced to evaluate the relative contribution of wind-driven (U10) and thermodynamically driven (ΔT and Δq) ocean heat uptake. Previously unnoticed salient properties of these formulas, reported here, are as follows: 1) these functions are hyperbolic and 2) increasing Δq is an efficient mechanism for enhancing the fluxes. This new perspective was used to investigate surface heat fluxes in six TCs during phases of steady-state intensity (SS), slow intensification (SI), and rapid intensification (RI). A capping of wind-driven heat uptake was found during periods of SS, SI, and RI. Compensation by larger values of Δq > 5 g kg−1 at moderate values of U10 led to intense inner-core moisture fluxes of greater than 600 W m−2 during RI. Peak values in Δq preferentially occurred over oceanic regimes with higher sea surface temperature (SST) and upper-ocean heat content. Thus, increasing SST and Δq is a very effective way to increase surface heat fluxes—this can easily be achieved as a TC moves over deeper warm oceanic regimes.

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