The impact of SST front on the surface wind in the southern Indian Ocean

2020 ◽  
Author(s):  
Xuhua Cheng
Keyword(s):  
Indian Ocean ◽  
Deep Convection ◽  
Surface Wind ◽  
Polar Front ◽  
Open Ocean ◽  
Heat Fluxes ◽  
Southern Indian Ocean ◽  
Sst Front ◽  
Microwave Imager ◽  
The Impact

<p><span> </span>Using 28-year satellite-borne Special Sensor Microwave Imager observations, features of high-wind frequency (HWF) over</p><p>the southern Indian Ocean are investigated. Climatology maps show that high winds occur frequently during austral winter,</p><p>located in the open ocean south of Polar Front in subpolar region, warm flank of the Subantarctic Front between 55<sup>o</sup>E-78<sup>o</sup>E, </p><p>and south of Cape Agulhas, where westerly wind prevails. The strong instability of marine atmospheric boundary layer</p><p>accompanied by increased sensible and latent heat fluxes on the warmer flank acts to enhance the vertical momentum mixing,</p><p>thus accelerate the surface winds. Effects of sea surface temperature (SST) front can even reach the entire troposphere</p><p>by deep convection. HWF also shows distinct interannual variability, which is associated with the Southern Annual Mode</p><p>(SAM). During positive phase of the SAM, HWF has positive anomalies over the open ocean south of Polar Front, while</p><p>has negative anomalies north of the SST front. A phase shift of HWF happened around 2001, which is likely related to the</p><p>reduction of storm tracks and poleward shift of westerly winds in the Southern Hemisphere.</p>

SST front anchored mesoscale feature of surface wind in the southern Indian Ocean

2019 ◽  
Vol 53 (1-2) ◽  
pp. 477-490 ◽  
Author(s):  
Xia Huang ◽  
Xuhua Cheng ◽  
Yiquan Qi
Keyword(s):  
Indian Ocean ◽  
Surface Wind ◽  
Southern Indian Ocean ◽  
Sst Front ◽  
Mesoscale Feature

scholarly journals Effect of deep convection on the TTL composition over the Southwest Indian Ocean during austral summer

2020 ◽  
Author(s):  
Stephanie Evan ◽  
Jerome Brioude ◽  
Karen Rosenlof ◽  
Sean M. Davis ◽  
Hölger Vömel ◽  
...  
Keyword(s):  
Water Vapor ◽  
Indian Ocean ◽  
Tropical Cyclones ◽  
Deep Convection ◽  
Austral Summer ◽  
Active Regions ◽  
Lagrangian Model ◽  
Southwest Indian Ocean ◽  
Tropopause Region ◽  
The Impact

Abstract. Balloon-borne measurements of CFH water vapor, ozone and temperature and water vapor lidar measurements from the Maïdo Observatory at Réunion Island in the Southwest Indian Ocean (SWIO) were used to study tropical cyclones' influence on TTL composition. The balloon launches were specifically planned using a Lagrangian model and METEOSAT 7 infrared images to sample the convective outflow from Tropical Storm (TS) Corentin on 25 January 2016 and Tropical Cyclone (TC) Enawo on 3 March 2017. Comparing CFH profile to MLS monthly climatologies, water vapor anomalies were identified. Positive anomalies of water vapor and temperature, and negative anomalies of ozone between 12 and 15 km in altitude (247 to 121 hPa) originated from convectively active regions of TS Corentin and TC Enawo, one day before the planned balloon launches, according to the Lagrangian trajectories. Near the tropopause region, air masses on 25 January 2016 were anomalously dry around 100 hPa and were traced back to TS Corentin active convective region where cirrus clouds and deep convective clouds may have dried the layer. An anomalously wet layer around 68 hPa was traced back to the South East IO where a monthly water vapor anomaly of 0.5 ppbv was observed. In contrast, no water vapor anomaly was found near or above the tropopause region on 3 March 2017 over Maïdo as the tropopause region was not downwind of TC Enawo. This study compares and contrasts the impact of two tropical cyclones on the humidification of the TTL over the Southwest Indian Ocean.

The Impact of Outer-Core Surface Heat Fluxes on the Convective Activities and Rapid Intensification of Tropical Cyclones

2020 ◽  
Vol 77 (11) ◽  
pp. 3907-3927
Author(s):  
Chin-Hsuan Peng ◽  
Chun-Chieh Wu
Keyword(s):  
Inner Core ◽  
Surface Wind ◽  
Outer Core ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Intensity Change ◽  
Rapid Intensification ◽  
Core Surface ◽  
Surface Heat Fluxes ◽  
The Impact

AbstractThe rapid intensification (RI) of Typhoon Soudelor (2015) is simulated using a full-physics model. To investigate how the outer-core surface heat fluxes affect tropical cyclone (TC) structure and RI processes, a series of numerical experiments are performed by suppressing surface heat fluxes between various radii. It is found that a TC would become quite weaker when the surface heat fluxes are suppressed outside the radius of 60 or 90 km [the radius of maximum surface wind in the control experiment (CTRL) at the onset of RI is roughly 60 km]. However, interestingly, the TC would experience stronger RI when the surface heat fluxes are suppressed outside the radius of 150 km. For those sensitivity experiments with capped surface heat fluxes, the members with greater intensification rate show stronger inner-core mid- to upper-level updrafts and higher heating efficiency prior to the RI periods. Although the outer-core surface heat fluxes in these members are suppressed, the inner-core winds become stronger, extracting more ocean energy from the inner core. Greater outer-core low-level stability in these members results in aggregation of deep convection and subsequent generation and concentration of potential vorticity inside the inner core, thus confining the strongest winds therein. The abovementioned findings are also supported by partial-correlation analyses, which reveal the positive correlation between the inner-core convection and subsequent 6-h intensity change, and the competition between the inner-core and outer-core convections (i.e., eyewall and outer rainbands).

scholarly journals The Impact of Variational Assimilation of SSM/I and QuikSCAT Satellite Observations on the Numerical Simulation of Indian Ocean Tropical Cyclones

2008 ◽  
Vol 23 (3) ◽  
pp. 460-476 ◽  
Author(s):  
Randhir Singh ◽  
P. K. Pal ◽  
C. M. Kishtawal ◽  
P. C. Joshi
Keyword(s):  
Indian Ocean ◽  
Bay Of Bengal ◽  
Mesoscale Model ◽  
Initial Conditions ◽  
Lower Troposphere ◽  
Heat Fluxes ◽  
Cyclone Intensity ◽  
Wind Speeds ◽  
The Impact ◽  
Quikscat Winds

Abstract In this study, the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) with three-dimensional variational data assimilation (3DVAR) is utilized to investigate the influence of Special Sensor Microwave Imager (SSM/I) and Quick Scatterometer (QuikSCAT) observations on the prediction of an Indian Ocean tropical cyclone. The 3DVAR sensitivity runs were conducted separately with QuikSCAT wind vectors, SSM/I wind speeds, and total precipitable water (TPW) to investigate their individual impact on cyclone intensity and track. The Orissa supercyclone over the Bay of Bengal during October 1999 was used for simulation and assimilation experiments. Assimilation of the QuikSCAT wind vector improves the initial position of the cyclone’s center with a position error of 33 km, which was 163 km in the background analysis. Incorporation of QuikSCAT winds was found to increase the air–sea heat fluxes over the cyclonic region, which resulted in the improved simulated intensity when compared with the simulation made without QuikSCAT winds in the initial conditions. The cyclone track improved significantly with assimilation of QuikSCAT wind vectors. The track improvement resulted from relocation of the initial cyclonic vortex after assimilation of QuikSCAT wind vectors. Like QuikSCAT, assimilation of SSM/I wind speeds strengthened the cyclonic circulation in the initial conditions. This increase in the low-level wind speeds enhanced the air–sea exchange processes and improved the simulated intensity of the cyclone. The lack of information about the wind direction from SSM/I prevented it from making much of an impact on track prediction. As compared to the first guess, assimilation of the SSM/I TPW shows a moistening of the lower troposphere over most of the Bay of Bengal except over the central region of the cyclone, where the assimilation of SSM/I TPW reduces the lower-tropospheric moisture. This decrease of moisture in the TPW assimilation experiment resulted in a weak cyclone intensity.

scholarly journals Diagnosing Heat and Vorticity Budgets of Annual Coupled Rossby Waves

2005 ◽  
Vol 35 (7) ◽  
pp. 1173-1189 ◽  
Author(s):  
Warren B. White ◽  
Jeffrey L. Annis
Keyword(s):  
Indian Ocean ◽  
Latent Heat ◽  
Rossby Waves ◽  
Surface Wind ◽  
Phase Speed ◽  
Western Indian Ocean ◽  
Heat Fluxes ◽  
Eastern Indian Ocean ◽  
Wind Stress Curl ◽  
Upper Level

Abstract Annual coupled Rossby waves are generated at the west coast of Australia and propagate westward across the eastern Indian Ocean from 10° to 30°S in covarying sea level height (SLH), sea surface temperature (SST), and meridional surface wind (MSW) residuals, generally traveling slower than uncoupled Rossby waves while increasing amplitude. The waves decouple in the western Indian Ocean as SST and SLH residuals become decorrelated, with wave amplitudes decreasing and westward phase speeds increasing. Here, the ocean and atmosphere thermal and vorticity budgets of the coupled Rossby waves in the eastern Indian Ocean along 20°S are diagnosed. In the upper ocean, these diagnostics find the residual SST tendency driven by the residual meridional geostrophic advection of mean temperature with warm SST residuals dissipated by upward latent heat flux to the atmosphere. In the troposphere, these upward latent heat fluxes drive mid-to-upper-level residual diabatic heating via excess condensation, balanced there by upward residual vertical thermal advection. The resulting upward residual vertical velocity drives residual upper-level divergence and lower-level convergence, the latter balanced in the troposphere vorticity budget by the residual meridional advection of planetary vorticity. This yields poleward MSW residuals collocated with warm SST residuals, as observed. The SLH tendency is modified by a positive feedback from wind stress curl residuals, the latter acting to increase the amplitude and decrease the westward phase speed of the wave. These diagnostics allow a more exact analytical model for coupled Rossby waves to be constructed, yielding wave characteristics as observed.

Pareto Optimization for Rossby Wave Pattern Impacts on MH370 Debris

2020 ◽  
pp. 251-280
Keyword(s):  
Indian Ocean ◽  
Rossby Waves ◽  
Wave Pattern ◽  
Pareto Optimization ◽  
Southern Indian Ocean ◽  
Reunion Island ◽  
Réunion Island ◽  
Ocean Gyres ◽  
Western Side ◽  
The Impact

This chapter censoriously appraises the comprehensive theories that specify that more concepts are needed to bridge the gap found between the dynamic of the Southern Indian Ocean and the actual MH370 vanishing mechanism. Thus, this chapter is devoted to the Rossby waves, which could attribute to the fact that the MH370 flaperon got to Réunion Island. In this view, Rossby waves generate growth of energy in the west of the ocean gyres and create the strengthening currents on the western side of the ocean basins. Pareto optimization algorithm of the impact power of Rossby waves proves that the flaperon could not drift across the Southern Indian Ocean and be positioned on Réunion Island.

scholarly journals Interhemispheric SST Gradient Trends in the Indian Ocean prior to and during the Recent Global Warming Hiatusa

2016 ◽  
Vol 29 (24) ◽  
pp. 9077-9095 ◽  
Author(s):  
Lu Dong ◽  
Michael J. McPhaden
Keyword(s):  
Global Warming ◽  
Indian Ocean ◽  
Wind Stress ◽  
Coastal Upwelling ◽  
Surface Wind ◽  
Heat Fluxes ◽  
Thermocline Depth ◽  
Upwelled Water ◽  
The Indian Ocean ◽  
Sst Gradient

Abstract Sea surface temperatures (SSTs) have been rising for decades in the Indian Ocean in response to greenhouse gas forcing. However, this study shows that during the recent hiatus in global warming, a striking interhemispheric gradient in Indian Ocean SST trends developed around 2000, with relatively weak or little warming to the north of 10°S and accelerated warming to the south of 10°S. Evidence is presented from a wide variety of data sources showing that this interhemispheric gradient in SST trends is forced primarily by an increase of Indonesian Throughflow (ITF) transport from the Pacific into the Indian Ocean induced by stronger Pacific trade winds. This increased transport led to a depression of the thermocline that facilitated SST warming, presumably through a reduction in the vertical turbulent transport of heat in the southern Indian Ocean. Surface wind changes in the Indian Ocean linked to the enhanced Walker circulation also may have contributed to thermocline depth variations and associated SST changes, with downwelling-favorable wind stress curls between 10° and 20°S and upwelling-favorable wind stress curls between the equator and 10°S. In addition, the anomalous southwesterly wind stresses off the coast of Somalia favored intensified coastal upwelling and offshore advection of upwelled water, which would have led to reduced warming of the northern Indian Ocean. Although highly uncertain, lateral heat advection associated with the ITF and surface heat fluxes may also have played a role in forming the interhemispheric SST gradient change.

Why Flight MH370 Has Not Vanished in the Southern Indian Ocean

2020 ◽  
pp. 310-331
Keyword(s):  
Indian Ocean ◽  
Ocean Dynamics ◽  
Southern Indian Ocean ◽  
Kuala Lumpur ◽  
Critical Question ◽  
Departure Point ◽  
Multiobjective Genetic Algorithm ◽  
Final Destination ◽  
Diego Garcia ◽  
The Impact

This chapter delivers the final conclusions that were raised due to the critical question of why MH370 has not ended up in the Southern Indian Ocean. In this view, the application of the multiobjective genetic algorithm is implemented to explore the final destination of MH370. The results show that the MH370's last destination is not near the coastal water of Perth, Australia as obtained by using a multiobjective algorithm. In this understanding, the Pareto optimization has allowed the author to see the impact of the Southern Indian Ocean dynamics on the MH370 debris trajectory movements. Moreover, the Pareto front verified that the found fragments do not belong to MH370 fuselage. There is a 95% confidence level that the flight found in Cambodia is not MH370. Finally, MH370 has been hijacked and driven to Diego Garcia as it is a short route from the departure point at International Malaysia Airport, Kuala Lumpur (KLIA).

scholarly journals The Impact of Moist Frontogenesis and Tropopause Undulation on the Intensity, Size, and Structural Changes of Hurricane Sandy (2012)

2017 ◽  
Vol 74 (3) ◽  
pp. 893-913 ◽  
Author(s):  
Jung Hoon Shin ◽  
Da-Lin Zhang
Keyword(s):  
Structural Changes ◽  
Deep Convection ◽  
Surface Wind ◽  
Vertical Wind Shear ◽  
Hurricane Sandy ◽  
Maximum Surface ◽  
Intensity Changes ◽  
Surrounding Areas ◽  
Two Stages ◽  
The Impact

Abstract This study examines the relative roles of moist frontogenesis and tropopause undulation in determining the intensity, size, and structural changes of Hurricane Sandy using a high-resolution cloud-resolving model. A 138-h simulation reproduces Sandy’s four distinct development stages: (i) rapid intensification, (ii) weakening, (iii) steady maximum surface wind but with large continued sea level pressure (SLP) falls, and (iv) reintensification. Results show typical correlations between intensity changes, sea surface temperature, and vertical wind shear during the first two stages. The large SLP falls during the last two stages are mostly caused by Sandy’s northward movement into lower-tropopause regions associated with an eastward-propagating midlatitude trough, where the associated lower-stratospheric warm air wraps into the storm and its surrounding areas. The steady maximum surface wind occurs because of the widespread SLP falls with weak gradients lacking significant inward advection of absolute angular momentum (AAM). Meanwhile, three spiral frontogenetic zones and associated rainbands develop internally in the outer northeastern quadrant during the last three stages when Sandy’s southeasterly warm current converges with an easterly cold current associated with an eastern Canadian high. Cyclonic inward advection of AAM along each frontal rainband accounts for the continued expansion of the tropical storm–force wind and structural changes, while deep convection in the eyewall and merging of the final two surviving frontogenetic zones generate a spiraling jet in Sandy’s northwestern quadrant, leading to its reintensification prior to landfall. The authors conclude that a series of moist frontogenesis plays a more important role than the lower-stratospheric warmth in determining Sandy’s size, intensity, and structural changes.

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