scholarly journals The Influence of the Barrier Layer on SST Response during Tropical Cyclone Wind Forcing Using Idealized Experiments

2018 ◽  
Vol 48 (7) ◽  
pp. 1471-1478 ◽  
Author(s):  
Johna E. Rudzin ◽  
Lynn K. Shay ◽  
William E. Johns
Keyword(s):  
Mixed Layer ◽  
Barrier Layer ◽  
Wind Forcing ◽  
Upper Ocean ◽  
Salinity Stratification ◽  
Sst Cooling ◽  
Temperature Regimes ◽  
Moisture Fluxes ◽  
Upper Ocean Response ◽  
Heat And Moisture

AbstractMultiple studies have shown that reduced sea surface temperature (SST) cooling occurs under tropical cyclones (TCs) where a fresh surface layer and subsurface halocline exist. Reduced SST cooling in these scenarios has been attributed to a barrier layer, an upper-ocean feature in the tropical global oceans in which a halocline resides within the isothermal mixed layer. Because upper-ocean stratification theoretically reduces ocean mixing induced by winds, the barrier layer is thought to reduce SST cooling during TC passage, sustaining heat and moisture fluxes into the storm. This research examines how both the inclusion of salinity and upper-ocean salinity stratification influences SST cooling for a variety of upper-ocean thermal regimes using one-dimensional (1D) ocean mixed layer (OML) models. The Kraus–Turner, Price–Weller–Pinkel, and Pollard–Rhines–Thompson 1D OML schemes are used to examine SST cooling and OML deepening during 30 m s−1 wind forcing (~category 1 TC) for both temperature-only and temperature–salinity stratification cases. Generally, the inclusion of salinity (a barrier layer) reduces SST cooling for all temperature regimes. However, results suggest that SST cooling sensitivities exist depending on thermal regime, salinity stratification, and the 1D OML model used. Upper-ocean thermal and haline characteristics are put into context of SST cooling with the creation of a barrier layer baroclinic wave speed to emphasize the influence of salinity stratification on upper-ocean response under TC wind forcing.

scholarly journals Upper-Ocean Response to Hurricane Frances (2004) Observed by Profiling EM-APEX Floats*

2011 ◽  
Vol 41 (6) ◽  
pp. 1041-1056 ◽  
Author(s):  
Thomas B. Sanford ◽  
James F. Price ◽  
James B. Girton
Keyword(s):  
Drag Coefficient ◽  
Vertical Mixing ◽  
Ocean Model ◽  
Upper Ocean ◽  
Surface Mixed Layer ◽  
Wind Speeds ◽  
Sst Cooling ◽  
Ocean Response ◽  
Upper Ocean Response ◽  
The Right

Abstract Three autonomous profiling Electromagnetic Autonomous Profiling Explorer (EM-APEX) floats were air deployed one day in advance of the passage of Hurricane Frances (2004) as part of the Coupled Boundary Layer Air–Sea Transfer (CBLAST)-High field experiment. The floats were deliberately deployed at locations on the hurricane track, 55 km to the right of the track, and 110 km to the right of the track. These floats provided profile measurements between 30 and 200 m of in situ temperature, salinity, and horizontal velocity every half hour during the hurricane passage and for several weeks afterward. Some aspects of the observed response were similar at the three locations—the dominance of near-inertial horizontal currents and the phase of these currents—whereas other aspects were different. The largest-amplitude inertial currents were observed at the 55-km site, where SST cooled the most, by about 2.2°C, as the surface mixed layer deepened by about 80 m. Based on the time–depth evolution of the Richardson number and comparisons with a numerical ocean model, it is concluded that SST cooled primarily because of shear-induced vertical mixing that served to bring deeper, cooler water into the surface layer. Surface gravity waves, estimated from the observed high-frequency velocity, reached an estimated 12-m significant wave height at the 55-km site. Along the track, there was lesser amplitude inertial motion and SST cooling, only about 1.2°C, though there was greater upwelling, about 25-m amplitude, and inertial pumping, also about 25-m amplitude. Previously reported numerical simulations of the upper-ocean response are in reasonable agreement with these EM-APEX observations provided that a high wind speed–saturated drag coefficient is used to estimate the wind stress. A direct inference of the drag coefficient CD is drawn from the momentum budget. For wind speeds of 32–47 m s−1, CD ~ 1.4 × 10−3.

Observations of the upper ocean response to storm forcing in the South Atlantic Roaring Forties

1995 ◽  
Vol 13 (10) ◽  
pp. 1027-1038 ◽  
Author(s):  
R. Marsh
Keyword(s):  
Mixed Layer ◽  
Austral Summer ◽  
South Atlantic ◽  
Upper Ocean ◽  
Surface Cooling ◽  
Ocean Response ◽  
Wind Event ◽  
Close Proximity ◽  
Upper Ocean Response ◽  
Inertial Currents

Abstract. In the austral summer of 1992–1993 the passage of a storm system drove a strong upper ocean response at 45°S in the mid-South Atlantic. Good in situ observations were obtained. CTD casts revealed that the mixed layer deepened by ~40 m over 4 days. Wind stirring dominated over buoyancy flux-driven mixing during the onset of high winds. Doppler shear currents further reveal this to be intimately related to inertial dynamics. The penetration depth of inertial currents, which are confined to the mixed layer, increases with time after a wind event, matched by a downward propagation of low values of the Richardson number. This suggests that inertial current shear is instrumental in producing turbulence at the base of the mixed layer. Evolution of inertial transport is simulated using a time series of ship-observed wind stress. Simulated transport is only 30–50% of the observed transport, suggesting that much of the observed inertial motion was forced by an earlier (possibly remote) storm. Close proximity of the subtropical front further complicates the upper ocean response to the storm. A simple heat balance for the upper 100 m reveals that surface cooling and mixing (during the storm) can account for only a small fraction of an apparent ~1 °C mixed layer cooling.

scholarly journals Upper Oceanic Energy Response to Tropical Cyclone Passage

2013 ◽  
Vol 26 (8) ◽  
pp. 2631-2650 ◽  
Author(s):  
John A. Knaff ◽  
Mark DeMaria ◽  
Charles R. Sampson ◽  
James E. Peak ◽  
James Cummings ◽  
...  
Keyword(s):  
Tropical Cyclone ◽  
Energy Content ◽  
Energy Conditions ◽  
Upper Ocean ◽  
Ocean Energy ◽  
Translation Speed ◽  
Structure Information ◽  
Sst Cooling ◽  
Ocean Response ◽  
Upper Ocean Response

Abstract The upper oceanic temporal response to tropical cyclone (TC) passage is investigated using a 6-yr daily record of data-driven analyses of two measures of upper ocean energy content based on the U.S. Navy’s Coupled Ocean Data Assimilation System and TC best-track records. Composite analyses of these data at points along the TC track are used to investigate the type, magnitude, and persistence of upper ocean response to TC passage, and to infer relationships between routinely available TC information and the upper ocean response. Upper oceanic energy decreases in these metrics are shown to persist for at least 30 days—long enough to possibly affect future TCs. Results also indicate that TC kinetic energy (KE) should be considered when assessing TC impacts on the upper ocean, and that existing TC best-track structure information, which is used here to estimate KE, is sufficient for such endeavors. Analyses also lead to recommendations concerning metrics of upper ocean energy. Finally, parameterizations for the lagged, along-track, upper ocean response to TC passage are developed. These show that the sea surface temperature (SST) is best related to the KE and the latitude whereas the upper ocean energy is a function of KE, initial upper ocean energy conditions, and translation speed. These parameterizations imply that the 10-day lagged SST cooling is approximately 0.7°C for a “typical” TC at 30° latitude, whereas the same storm results in 10-day (30-day) lagged decreases of upper oceanic energy by about 12 (7) kJ cm−2 and a 0.5°C (0.3°C) cooling of the top 100 m of ocean.

scholarly journals Upper Ocean Response to Two Sequential Tropical Cyclones over the Northwestern Pacific Ocean

2019 ◽  
Vol 11 (20) ◽  
pp. 2431 ◽  
Author(s):  
Jue Ning ◽  
Qing Xu ◽  
Tao Feng ◽  
Han Zhang ◽  
Tao Wang
Keyword(s):  
Pacific Ocean ◽  
Tropical Cyclones ◽  
Mixed Layer ◽  
Upper Ocean ◽  
Northwestern Pacific ◽  
Northwestern Pacific Ocean ◽  
Surface Cooling ◽  
Chl A ◽  
Ocean Response ◽  
Upper Ocean Response

The upper ocean thermodynamic and biological responses to two sequential tropical cyclones (TCs) over the Northwestern Pacific Ocean were investigated using multi-satellite datasets, in situ observations and numerical model outputs. During Kalmaegi and Fung-Wong, three distinct cold patches were observed at sea surface. The locations of these cold patches are highly correlated with relatively shallower depth of the 26 °C isotherm and mixed layer depth (MLD) and lower upper ocean heat content. The enhancement of surface chlorophyll a (chl-a) concentration was detected in these three regions as well, mainly due to the TC-induced mixing and upwelling as well as the terrestrial runoff. Moreover, the pre-existing ocean cyclonic eddy (CE) has been found to significantly modulate the magnitude of surface cooling and chl-a increase. With the deepening of the MLD on the right side of TCs, the temperature of the mixed layer decreased and the salinity increased. The sequential TCs had superimposed effects on the upper ocean response. The possible causes of sudden track change in sequential TCs scenario were also explored. Both atmospheric and oceanic conditions play noticeable roles in abrupt northward turning of the subsequent TC Fung-Wong.

scholarly journals Upper-Ocean Response to Precipitation Forcing in an Ocean Model Hindcast of Hurricane Gonzalo

2020 ◽  
Vol 50 (11) ◽  
pp. 3219-3234
Author(s):  
John Steffen ◽  
Mark Bourassa
Keyword(s):  
Barrier Layer ◽  
Turbulent Mixing ◽  
Ocean Model ◽  
Upper Ocean ◽  
Freshwater Flux ◽  
Model Case ◽  
Near Surface ◽  
Ocean Stratification ◽  
Ocean Response ◽  
Upper Ocean Response

AbstractPreexisting, oceanic barrier layers have been shown to limit turbulent mixing and suppress mixed layer cooling during the forced stage of a tropical cyclone (TC). Furthermore, an understanding of barrier layer evolution during TC passage is mostly unexplored. High precipitation rates within TCs provide a large freshwater flux to the surface that alters upper-ocean stratification and can act as a potential mechanism to strengthen the barrier layer. Ocean glider observations from the Bermuda Institute of Ocean Sciences (BIOS) indicate that a strong barrier layer developed during the approach and passage of Hurricane Gonzalo (2014), primarily as a result of freshening within the upper 30 m of the ocean. Therefore, an ocean model case study of Hurricane Gonzalo has been designed to investigate how precipitation affects upper-ocean stratification and sea surface temperature (SST) cooling during TC passage. Ocean model hindcasts of Hurricane Gonzalo characterize the upper-ocean response to TC precipitation forcing. Three different vertical mixing parameterizations are tested to determine their sensitivity to precipitation forcing. For all turbulent mixing schemes, TC precipitation produces near-surface freshening of about 0.3 psu, which is consistent with previous studies and in situ ocean observations. The influence of precipitation-induced changes to the SST response is more complicated, but generally modifies SSTs by ±0.3°C. Precipitation forcing creates a dynamical coupling between upper-ocean stratification and current shear that is largely responsible for the heterogeneous response in modeled SSTs.

scholarly journals Effects of Precipitation on the Upper-Ocean Response to a Hurricane

2007 ◽  
Vol 135 (6) ◽  
pp. 2207-2225 ◽  
Author(s):  
S. Daniel Jacob ◽  
Chester J. Koblinsky
Keyword(s):  
Mixed Layer ◽  
Saline Water ◽  
Storm Track ◽  
Surface Fluxes ◽  
Upper Ocean ◽  
Salinity Response ◽  
Ocean Response ◽  
Freshwater Forcing ◽  
Upper Ocean Response ◽  
The Right

Abstract The effect of precipitation on the upper-ocean response during a tropical cyclone passage is investigated using a numerical model in this paper. For realistic wind forcing and empirical rain rates based on satellite climatology, numerical simulations are performed with and without precipitation forcing to delineate the effects of freshwater forcing on the upper-ocean heat and salt budgets. Additionally, the performance of five mixing parameterizations is also examined for the two forcing conditions to understand the sensitivity of simulated ocean response. Overall, results from 15 numerical experiments are analyzed to quantify the precipitation effects on the oceanic mixed layer and the upper ocean. Simulated fields for the same mixing scheme with and without precipitation indicate a decrease in the upper-ocean cooling of about 0.2°–0.5°C. This is mainly due to reduced mixing of colder water from below induced by the increased stability of the added freshwater. The cooler rainwater contributes a maximum of approximately 10% to the total surface heat loss from the ocean. The rate of freshening due to precipitation exceeds the rate of mixing of the more saline water from below, leading to a change in sign of the mixed layer salinity response. As seen in earlier studies, large uncertainty exists in the simulated upper-ocean response due to the choice of mixing parameterization. Although the nature of simulated response remains similar for all the mixing schemes, the magnitude of freshening and cooling varies by as much as 0.5 psu and 1°C between the schemes to the right of the storm track. While changes in the mixed layer and in the top 100 m of heat and salt budgets are strongly influenced by the choice of mixing scheme, integrated budgets in the top 200 m are seen to be affected more by advection and surface fluxes. However, since the estimated surface fluxes depend upon the simulated sea surface temperature, the choice of mixing scheme is crucial for realistic coupled predictive models.

scholarly journals Rapid Mixed Layer Deepening by the Combination of Langmuir and Shear Instabilities: A Case Study

2010 ◽  
Vol 40 (11) ◽  
pp. 2381-2400 ◽  
Author(s):  
Tobias Kukulka ◽  
Albert J. Plueddemann ◽  
John H. Trowbridge ◽  
Peter P. Sullivan
Keyword(s):  
Mixed Layer ◽  
Spatial Scales ◽  
Stokes Drift ◽  
Vertical Shear ◽  
Upper Ocean ◽  
Temperature Perturbation ◽  
Langmuir Circulation ◽  
Wind Event ◽  
Shear Instabilities ◽  
Upper Ocean Response

Abstract Langmuir circulation (LC) is a turbulent upper-ocean process driven by wind and surface waves that contributes significantly to the transport of momentum, heat, and mass in the oceanic surface layer. The authors have previously performed a direct comparison of large-eddy simulations and observations of the upper-ocean response to a wind event with rapid mixed layer deepening. The evolution of simulated crosswind velocity variance and spatial scales, as well as mixed layer deepening, was only consistent with observations if LC effects are included in the model. Based on an analysis of these validated simulations, in this study the fundamental differences in mixing between purely shear-driven turbulence and turbulence with LC are identified. In the former case, turbulent kinetic energy (TKE) production due to shear instabilities is largest near the surface, gradually decreasing to zero near the base of the mixed layer. This stands in contrast to the LC case in which at middepth range TKE production can be dominated by Stokes drift shear. Furthermore, the Eulerian mean vertical shear peaks near the base of the mixed layer so that TKE production by mean shear flow is elevated there. LC transports horizontal momentum efficiently downward leading to an along-wind velocity jet below LC downwelling regions at the base of the mixed layer. Locally enhanced vertical shear instabilities as a result of this jet efficiently erode the thermocline. In turn, enhanced breaking internal waves inject cold deep water into the mixed layer, where LC currents transport temperature perturbation advectively. Thus, LC and locally generated shear instabilities work intimately together to facilitate strongly the mixed layer deepening process.

scholarly journals Upper Ocean Response to Rain Observed From a Vertical Profiler

2019 ◽  
Vol 124 (6) ◽  
pp. 3664-3681 ◽  
Author(s):  
A. Doeschate ◽  
G. Sutherland ◽  
H. Bellenger ◽  
S. Landwehr ◽  
L. Esters ◽  
...  
Keyword(s):  
Upper Ocean ◽  
Ocean Response ◽  
Upper Ocean Response
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