scholarly journals Low-Level Cool Air over the Midlatitude Oceans in Summer

2018 ◽  
Vol 31 (5) ◽  
pp. 2075-2090 ◽  
Author(s):  
Teruhisa Shimada ◽  
Yuki Kanno ◽  
Toshiki Iwasaki
Keyword(s):  
Southern Hemisphere ◽  
Coastal Upwelling ◽  
Heat Content ◽  
Warm Season ◽  
Heat Fluxes ◽  
Systematic Analysis ◽  
Surface Heat Fluxes ◽  
Low Level ◽  
Basin Scale ◽  
Subtropical Oceans

The climatology of low-level cool air over the midlatitude oceans in summer is presented based on an isentropic analysis. This study focuses on isentropic surfaces of 296 K to analyze an adiabatic invariant referred to as the negative heat content representing the coldness of the air layer below the threshold isentropic surface. This approach allows a systematic analysis and a quantitative comparison of the cool air distribution and a diagnosis of diabatic heating of the air mass. The cool air covers most of the subarctic oceans and extends equatorward over the coastal upwelling regions in the east of the ocean basins. In these regions, the genesis of the cool air is diagnosed. The loss of the cool air occurs over land and the subtropical oceans, particularly on the offshore side of the coastal upwelling regions. In the Pacific sector and the Indian Ocean sector of the Southern Ocean, another large loss of the cool air occurs along the oceanic frontal zone including the Agulhas Return Current. Over the zonally extended region where the cool air is generated in the Southern Hemisphere and the coastal upwelling regions, it is suggested that diabatic cooling associated with low-level clouds overcome heating by turbulent surface heat fluxes. The genesis of the cool air over the subarctic oceans in the Northern Hemisphere in the warm season switches into the loss of the cold air in the cool season on a basin scale. Meanwhile, over the oceans in the Southern Hemisphere, there is no basin-scale seasonal switch.

A Rarely Witnessed Summertime Upwelling Event northwest off the Hainan Island

2020 ◽  
Author(s):  
Ai-Jun Pan ◽  
Fang-fang Kuang ◽  
Kai Li ◽  
Xu Dong
Keyword(s):  
Coastal Upwelling ◽  
Hainan Island ◽  
Heat Fluxes ◽  
Tidal Mixing ◽  
Coastal Current ◽  
Beibu Gulf ◽  
Surface Heat Fluxes ◽  
Upwelled Water ◽  
Basin Scale ◽  
Upwelling Event

<p>A field survey revealed a rare realization of upwelling event in the northwestern Hainan Island (UNWHI) on July 24, 2015. Model experiments suggest that the UNWHI is not locally generated, but can be treated as northward extension of the upwelling southwest off Hainan Island (USWHI) under favorable wind conditions. Therefore, presence of the USWHI is vital for the UNWHI occurrence. Tidal mixing is testified to be the primary driving force for the USWHI, whilst southerly winds plays an essential role in the induction of the UNWHI. Moreover, it is demonstrated that the UNWHI is not a stable, but intermittent coastal upwelling system. Shallow basin of the Beibu Gulf makes the interior circulation vulnerable to local monsoon changes. Given the favorable southerly winds, a cyclonic gyre northwest off Hainan Island will be induced and which, leads to northward coastal current and consequently, the UNWHI is to be formed due to the northward transport of the USWHI. Conversely, the UNWHI vanishes during northerly winds period, because the basin-scale anticyclonic gyre results in a southward current west off the Hainan Island and which, acts to push the upwelled water of the USWHI offshore and away from the northwestern Hainan Island. In addition, our diagnostics indicates that contributions from surface heat fluxes to the UNWHI occurrence is negligible. Besides, it also reminds us that application of a high-frequency, much closer to reality wind field is necessary for the coastal upwelling simulation. </p>

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.

On the Accuracy of the Simple Ocean Data Assimilation Analysis for Estimating Heat Budgets of the Near-Surface Arabian Sea and Bay of Bengal*

2005 ◽  
Vol 35 (3) ◽  
pp. 395-400 ◽  
Author(s):  
S S C. Shenoi ◽  
D. Shankar ◽  
S. R. Shetye
Keyword(s):  
Data Assimilation ◽  
Bay Of Bengal ◽  
Arabian Sea ◽  
Heat Budget ◽  
Heat Content ◽  
Heat Fluxes ◽  
Simple Ocean Data Assimilation ◽  
Near Surface ◽  
Surface Heat Fluxes ◽  
Ocean Data Assimilation

Abstract The accuracy of data from the Simple Ocean Data Assimilation (SODA) model for estimating the heat budget of the upper ocean is tested in the Arabian Sea and the Bay of Bengal. SODA is able to reproduce the changes in heat content when they are forced more by the winds, as in wind-forced mixing, upwelling, and advection, but not when they are forced exclusively by surface heat fluxes, as in the warming before the summer monsoon.

Long-term global ocean heat content change driven by sub-polar surface heat fluxes

2020 ◽  
Author(s):  
Taimoor Sohail ◽  
Damien B Irving ◽  
Jan David Zika ◽  
Ryan M Holmes ◽  
John Alexander Church
Keyword(s):  
Heat Content ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Ocean Heat Content ◽  
Global Ocean ◽  
Polar Surface ◽  
Surface Heat Fluxes ◽  
Content Change

scholarly journals The Value of Sustained Ocean Observations for Sea Ice Predictions in the Barents Sea

2019 ◽  
Vol 32 (20) ◽  
pp. 7017-7035 ◽  
Author(s):  
Mitchell Bushuk ◽  
Xiaosong Yang ◽  
Michael Winton ◽  
Rym Msadek ◽  
Matthew Harrison ◽  
...  
Keyword(s):  
Sea Ice ◽  
Barents Sea ◽  
Initial Conditions ◽  
Heat Budget ◽  
Heat Content ◽  
Arctic Sea Ice ◽  
Heat Fluxes ◽  
Seasonal Forecasts ◽  
Surface Heat Fluxes ◽  
The Barents Sea

ABSTRACT Dynamical prediction systems have shown potential to meet the emerging need for seasonal forecasts of regional Arctic sea ice. Observationally constrained initial conditions are a key source of skill for these predictions, but the direct influence of different observation types on prediction skill has not yet been systematically investigated. In this work, we perform a hierarchy of observing system experiments with a coupled global data assimilation and prediction system to assess the value of different classes of oceanic and atmospheric observations for seasonal sea ice predictions in the Barents Sea. We find notable skill improvements due to the inclusion of both sea surface temperature (SST) satellite observations and subsurface conductivity–temperature–depth (CTD) measurements. The SST data are found to provide the crucial source of interannual variability, whereas the CTD data primarily provide climatological and trend improvements. Analysis of the Barents Sea ocean heat budget suggests that ocean heat content anomalies in this region are driven by surface heat fluxes on seasonal time scales.

The Role of Low-Level Flow Direction on Tropical Cyclone Intensity Changes in a Moderate-Sheared Environment

2021 ◽  
Author(s):  
Tsung-Yung Lee ◽  
Chun-Chieh Wu ◽  
Rosimar Rios-Berrios
Keyword(s):  
Inner Core ◽  
Deep Layer ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Background Flow ◽  
Surface Heat Fluxes ◽  
Low Level ◽  
Flow Profiles ◽  
Group Experiences ◽  
The Impact

AbstractThe impact of low-level flow (LLF) direction on the intensification of intense tropical cyclones under moderate deep-layer shear is investigated based on idealized numerical experiments. The background flow profiles are constructed by varying the LLF direction with the same moderate deep-layer shear. When the maximum surface wind speed of the simulation without background flow reaches 70 knots, the background flow profiles are imposed. After a weakening period in the first 12 h, the members with upshear-left-pointing LLF (fast-intensifying group) intensify faster between 12–24 h than those members (slow-intensifying group) with downshear-right-pointing LLF. The fast-intensifying group experiences earlier development of inner-core structures after 12 h, such as potential vorticity below the mid-troposphere, upper-level warm core, eyewall axisymmmetrization, and moist entropy gradient, while the inner-core features of the slow-intensifying group remain relatively weak and asymmetric. The FI group experiences smaller tilt increase and stronger mid-level PV ring development. The upshear-left convection during 6–12 h is responsible for the earlier development of the inner core by reducing ventilation, providing axisymmetric heating and benefiting the eyewall development. The LLF of the fast-intensifying group enhances surface heat fluxes in the downshear side, resulting in higher energy supply to the upshear-left convection from the boundary layer. In all, this study provides new insights on the impact of LLF direction on intense storms under moderate shear by modulating the surface heat fluxes and eyewall convection.

Development of the temperature and salinity structure of the upper ocean over two months in an area 150x150 km

1983 ◽  
Vol 308 (1503) ◽  
pp. 311-325 ◽  
Keyword(s):  
Heat Budget ◽  
Salt Content ◽  
Heat Content ◽  
Time History ◽  
Heat Fluxes ◽  
Spatial Average ◽  
Survey Area ◽  
Surface Heat Fluxes ◽  
History Of ◽  
Salinity Structure

During the two months of the JASIN experiment a regular conductivity-temperaturedepth station pattern was worked by Hr. Neth. Ms. Tydeman , giving a total of eight surveys of temperature and salinity structure in an area 100 km x 150 km. The data are averaged to obtain hourly and spatial mean profiles. It is shown that this averaging conserves heat and salt content. The spatial mean profiles are compared with heat budget computations, and it is found that, on average, surface heat fluxes dominate the time history of the oceanic heat content on the scale of the whole survey area. On smaller scales advection due to mesoscale structures dominates, masking any differences in heating in different water masses. Comparison with results from a onedimensional mixed-layer model indicates that this type of model satisfactorily simulates the development of the temperature profile as a spatial average for the survey area.

scholarly journals Low-Level Jets over the Mid-Atlantic States: Warm-Season Climatology and a Case Study

2006 ◽  
Vol 45 (1) ◽  
pp. 194-209 ◽  
Author(s):  
Da-Lin Zhang ◽  
Shunli Zhang ◽  
Scott J. Weaver
Keyword(s):  
Real Time ◽  
Great Plains ◽  
Thermal Gradient ◽  
Warm Season ◽  
Heat Fluxes ◽  
Time Model ◽  
Low Level ◽  
Mountainous Regions ◽  
Low Level Jets

Abstract Although considerable research has been conducted to study the characteristics of the low-level jets (LLJs) over the Great Plains states, little is known about the development of LLJs over the Mid-Atlantic states. In this study, the Mid-Atlantic LLJ and its associated characteristics during the warm seasons of 2001 and 2002 are documented with both the wind profiler data and the daily real-time model forecast products. A case study with three model sensitivity simulations is performed to gain insight into the three-dimensional structures and evolution of an LLJ and the mechanisms by which it developed. It is found that the Mid-Atlantic LLJ, ranging from 8 to 23 m s−1, appeared at an average altitude of 670 m and on 15–25 days of each month. About 90% of the 160 observed LLJ events occurred between 0000 and 0600 LST, and about 60% had southerly to westerly directions. Statistically, the real-time forecasts capture most of the LLJ events with nearly the right timing, intensity, and altitude, although individual forecasts may not correspond to those observed. For a selected southwesterly LLJ case, both the observations and the control simulation exhibit a pronounced diurnal cycle of horizontal winds in the lowest 1.5 km. The simulation shows that the Appalachian Mountains tend to produce a sloping mixed layer with northeasterly thermal winds during the daytime and reversed thermal winds after midnight. With additional thermal contrast effects associated with the Chesapeake Bay and the Atlantic Ocean, the daytime low-level winds vary significantly from the east coast to the mountainous regions. The LLJ after midnight tends to be peaked preferentially around 77.5°W near the middle portion of the sloping terrain, and it decreases eastward as a result of the opposite thermal gradient across the coastline from the mountain-generated thermal gradient. Although the Mid-Atlantic LLJ is much weaker and less extensive than that over the Great Plains states, it has a width of 300–400 km (to its half-peak value) and a length scale of more than 1500 km, following closely the orientation of the Appalachians. Sensitivity simulations show that eliminating the surface heat fluxes produces the most significant impact on the development of the LLJ, then topography and the land–sea contrast, with its area-averaged intensity reduced from 12 m s−1 to about 6, 9, and 10 m s−1, respectively.

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