Enhanced wind-driven downwelling flow in warm oceanic eddy features during the intensification of tropical cyclone Isaac (2012)

Observations and theory

Benjamin Jaimes, Lynn K Shay

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

Tropical cyclones (TCs) typically produce intense oceanic upwelling underneath the storm's center and weaker and broader downwelling outside upwelled regions. However, several cases of predominantly downwelling responses over warm, anticyclonic mesoscale oceanic features were recently reported, where the ensuing upper-ocean warming prevented significant cooling of the sea surface, and TCs rapidly attained and maintained major status. Elucidating downwelling responses is critical to better understanding TC intensification over warm mesoscale oceanic features. Airborne ocean profilers deployed over the Gulf of Mexico's eddy features during the intensification of tropical storm Isaac into a hurricane measured isothermal downwelling of up to 60 m over a 12-h interval (5 m h-1) or twice the upwelling strength underneath the storm's center. This displacement occurred over a warm-core eddy that extended underneath Isaac's left side, where the ensuing upper-ocean warming was ~8 kW m-2; sea surface temperatures >28°C prevailed during Isaac's intensification. Rather than with just Ekman pumping WE, these observed upwelling-downwelling responses were consistent with a vertical velocity Ws = WE - Rogδ(Uh + UOML); Ws is the TC-driven pumping velocity, derived from the dominant vorticity balance that considers geostrophic flow strength (measured by the eddy Rossby number Rog = ζg/f), geostrophic vorticity ζg, Coriolis frequency f, aspect ratio δ = h/Rmax, oceanic mixed layer thickness h, storm's radius of maximum winds Rmax, total surface stresses from storm motion Uh, and oceanic mixed layer Ekman drift UOML. These results underscore the need for initializing coupled numerical models with realistic ocean states to correctly resolve the three-dimensional upwelling-downwelling responses and improve TC intensity forecasting.

Original languageEnglish (US)
Pages (from-to)1667-1689
Number of pages23
JournalJ. PHYSICAL OCEANOGRAPHY
Volume45
Issue number6
DOIs
StatePublished - 2015

Fingerprint

downwelling
tropical cyclone
eddy
upwelling
upper ocean
vorticity
mixed layer
warming
geostrophic flow
Ekman pumping
Rossby number
profiler
ocean
hurricane
pumping
sea surface
sea surface temperature
cooling

Keywords

  • Atm/Ocean Structure/ Phenomena
  • Atmosphere-ocean interaction
  • Circulation/ Dynamics
  • Eddies
  • Hurricanes/typhoons
  • Oceanic mixed layer
  • Upwelling/downwelling
  • Wind stress

ASJC Scopus subject areas

  • Oceanography

Cite this

@article{15084a9034cc4973a1e3a9fa11641f9b,
title = "Enhanced wind-driven downwelling flow in warm oceanic eddy features during the intensification of tropical cyclone Isaac (2012): Observations and theory",
abstract = "Tropical cyclones (TCs) typically produce intense oceanic upwelling underneath the storm's center and weaker and broader downwelling outside upwelled regions. However, several cases of predominantly downwelling responses over warm, anticyclonic mesoscale oceanic features were recently reported, where the ensuing upper-ocean warming prevented significant cooling of the sea surface, and TCs rapidly attained and maintained major status. Elucidating downwelling responses is critical to better understanding TC intensification over warm mesoscale oceanic features. Airborne ocean profilers deployed over the Gulf of Mexico's eddy features during the intensification of tropical storm Isaac into a hurricane measured isothermal downwelling of up to 60 m over a 12-h interval (5 m h-1) or twice the upwelling strength underneath the storm's center. This displacement occurred over a warm-core eddy that extended underneath Isaac's left side, where the ensuing upper-ocean warming was ~8 kW m-2; sea surface temperatures >28°C prevailed during Isaac's intensification. Rather than with just Ekman pumping WE, these observed upwelling-downwelling responses were consistent with a vertical velocity Ws = WE - Rogδ(Uh + UOML); Ws is the TC-driven pumping velocity, derived from the dominant vorticity balance that considers geostrophic flow strength (measured by the eddy Rossby number Rog = ζg/f), geostrophic vorticity ζg, Coriolis frequency f, aspect ratio δ = h/Rmax, oceanic mixed layer thickness h, storm's radius of maximum winds Rmax, total surface stresses from storm motion Uh, and oceanic mixed layer Ekman drift UOML. These results underscore the need for initializing coupled numerical models with realistic ocean states to correctly resolve the three-dimensional upwelling-downwelling responses and improve TC intensity forecasting.",
keywords = "Atm/Ocean Structure/ Phenomena, Atmosphere-ocean interaction, Circulation/ Dynamics, Eddies, Hurricanes/typhoons, Oceanic mixed layer, Upwelling/downwelling, Wind stress",
author = "Benjamin Jaimes and Shay, {Lynn K}",
year = "2015",
doi = "10.1175/JPO-D-14-0176.1",
language = "English (US)",
volume = "45",
pages = "1667--1689",
journal = "Journal of Physical Oceanography",
issn = "0022-3670",
publisher = "American Meteorological Society",
number = "6",

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TY - JOUR

T1 - Enhanced wind-driven downwelling flow in warm oceanic eddy features during the intensification of tropical cyclone Isaac (2012)

T2 - Observations and theory

AU - Jaimes, Benjamin

AU - Shay, Lynn K

PY - 2015

Y1 - 2015

N2 - Tropical cyclones (TCs) typically produce intense oceanic upwelling underneath the storm's center and weaker and broader downwelling outside upwelled regions. However, several cases of predominantly downwelling responses over warm, anticyclonic mesoscale oceanic features were recently reported, where the ensuing upper-ocean warming prevented significant cooling of the sea surface, and TCs rapidly attained and maintained major status. Elucidating downwelling responses is critical to better understanding TC intensification over warm mesoscale oceanic features. Airborne ocean profilers deployed over the Gulf of Mexico's eddy features during the intensification of tropical storm Isaac into a hurricane measured isothermal downwelling of up to 60 m over a 12-h interval (5 m h-1) or twice the upwelling strength underneath the storm's center. This displacement occurred over a warm-core eddy that extended underneath Isaac's left side, where the ensuing upper-ocean warming was ~8 kW m-2; sea surface temperatures >28°C prevailed during Isaac's intensification. Rather than with just Ekman pumping WE, these observed upwelling-downwelling responses were consistent with a vertical velocity Ws = WE - Rogδ(Uh + UOML); Ws is the TC-driven pumping velocity, derived from the dominant vorticity balance that considers geostrophic flow strength (measured by the eddy Rossby number Rog = ζg/f), geostrophic vorticity ζg, Coriolis frequency f, aspect ratio δ = h/Rmax, oceanic mixed layer thickness h, storm's radius of maximum winds Rmax, total surface stresses from storm motion Uh, and oceanic mixed layer Ekman drift UOML. These results underscore the need for initializing coupled numerical models with realistic ocean states to correctly resolve the three-dimensional upwelling-downwelling responses and improve TC intensity forecasting.

AB - Tropical cyclones (TCs) typically produce intense oceanic upwelling underneath the storm's center and weaker and broader downwelling outside upwelled regions. However, several cases of predominantly downwelling responses over warm, anticyclonic mesoscale oceanic features were recently reported, where the ensuing upper-ocean warming prevented significant cooling of the sea surface, and TCs rapidly attained and maintained major status. Elucidating downwelling responses is critical to better understanding TC intensification over warm mesoscale oceanic features. Airborne ocean profilers deployed over the Gulf of Mexico's eddy features during the intensification of tropical storm Isaac into a hurricane measured isothermal downwelling of up to 60 m over a 12-h interval (5 m h-1) or twice the upwelling strength underneath the storm's center. This displacement occurred over a warm-core eddy that extended underneath Isaac's left side, where the ensuing upper-ocean warming was ~8 kW m-2; sea surface temperatures >28°C prevailed during Isaac's intensification. Rather than with just Ekman pumping WE, these observed upwelling-downwelling responses were consistent with a vertical velocity Ws = WE - Rogδ(Uh + UOML); Ws is the TC-driven pumping velocity, derived from the dominant vorticity balance that considers geostrophic flow strength (measured by the eddy Rossby number Rog = ζg/f), geostrophic vorticity ζg, Coriolis frequency f, aspect ratio δ = h/Rmax, oceanic mixed layer thickness h, storm's radius of maximum winds Rmax, total surface stresses from storm motion Uh, and oceanic mixed layer Ekman drift UOML. These results underscore the need for initializing coupled numerical models with realistic ocean states to correctly resolve the three-dimensional upwelling-downwelling responses and improve TC intensity forecasting.

KW - Atm/Ocean Structure/ Phenomena

KW - Atmosphere-ocean interaction

KW - Circulation/ Dynamics

KW - Eddies

KW - Hurricanes/typhoons

KW - Oceanic mixed layer

KW - Upwelling/downwelling

KW - Wind stress

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U2 - 10.1175/JPO-D-14-0176.1

DO - 10.1175/JPO-D-14-0176.1

M3 - Article

VL - 45

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EP - 1689

JO - Journal of Physical Oceanography

JF - Journal of Physical Oceanography

SN - 0022-3670

IS - 6

ER -