httpglossaryametsocorgwiki Tropicalcyclone httpglossaryametsocorgwiki Tropicalcyclone Necessary but not sufficient conditions for tropical cyclogenesis Gray 1968 Although the initial mechanisms by which tropical cyclones might form can vary from ocean basin to ocean ID: 643365 Download Presentation
Ethan Wright: UNC Asheville. Research Advisor: . Dr. Christopher . Hennon. 04/22/2015. Peak Intensity: 190 mph. Lowest Pressure: 870 . mb. Small eye size of 8 nm . Super Typhoon Tip (1979). Super Typhoon Winnie (1997).
Satellite cl oud imageries are used along with other meteorological features to estimate t he intensities and the wind speed associated with these intense systems The satellite cl oud configurations expressed by T numbers have unique relati onship w
By. Dr. Mukta . Paliwal. CSE, IIT Bombay. Introduction. Tropical cyclones are low pressure systems that have thunderstorm activity and rotate counterclockwise.. Tropical cyclones form over all tropical oceanic areas except the South Atlantic and the Southeast Pacific. .
Madeline Frank. EAS 4480. Course Project. April 2016. Goals. 4 Ocean Basins:. . North Atlantic, East Pacific, West Pacific, . Indian. Determine the relationship (if any) between active and/or inactive tropical cyclone years among 4 Ocean basins.
SOES 6026 – Radar Remote Sensing. Ray Bell. Tropical cyclones. Applications. Scatterometers. Altimeters. SARs. Forecasting. Conclusions. Applications. Influence 10,000s people every year and can shape financial markets..
E. valuate the impacts of tropical . c. yclones on the integrated sea- surface chlorophyll in the subtropical North Atlantic. Approach. Use 14 years of tropical cyclone track data and satellite chlorophyll data for the period 1998-2011 .
Responding to a major disaster – lessons from cyclone PAM. Ettienne Ravo. Assistant Registrar General. Introduction & Country Back Ground. Vanuatu is an island nation of 271,089 people. There are 6 provinces with 14 main inhabited islands.
Storm surge. Storm tide. Extreme rainfall. Inland flooding. High winds. Tornadoes. Rip currents. The impacts of a tropical cyclone on people. > Business Area Here. Focus on Health and Wellbeing. We’re going to focus on the potential effects of a tropical cyclone on .
Weather Systems. The image above shows a . midlatitude. cyclone that was called the “1993 . Superstorm. ” and “The Storm of the Century.” This mid-March cyclone brought blizzard conditions to the E. coast. Mid-latitude cyclones are easy to identify .
http://glossary.ametsoc.org/wiki/. Tropical_cyclone. . http://glossary.ametsoc.org/wiki/. Tropical_cyclone. . Necessary, but not sufficient, conditions for tropical cyclogenesis. (Gray, 1968). Although the initial mechanisms by which tropical cyclones might form can vary from ocean basin to ocean basin, the process by which TCs develop should be similar globally.
Download Presentation - The PPT/PDF document "Tropical Cyclone Lifecycle Summary" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Tropical Cyclone Lifecycle Summary
Presentation on theme: "Tropical Cyclone Lifecycle Summary"— Presentation transcript:
Tropical Cyclone Lifecycle SummarySlide2
Necessary, but not sufficient, conditions for tropical cyclogenesis
Although the initial mechanisms by which tropical cyclones might form can vary from ocean basin to ocean basin, the process by which TCs develop should be similar globally
Gray (1968) proposed several necessary, but not sufficient, conditions necessary for tropical cyclogenesis:
Strong moisture convergence into the vortex caused by frictionally-forced low-level convergence (e.g., Ekman turning)
Accompanying upper-tropospheric divergence that leads to deep cumulus convectionSlightly more net divergence than convergence in the vortex columnHorizontal wind shear present in the lower troposphere, but minimal vertical wind shear Sea surface and deeper ocean temperature at or exceeding 26.5°C
Position poleward of at least 5° to invoke Coriolis turningA pre-existing low-level vorticity disturbanceSlide5
TC Lifecycle Stages & Characteristics
) boundary layer inflow (ii) eyewall (iii) cirrus shield (
iv) rainbands(v) upper tropospheric outflow
(vi) eye (usually > 100 kts)
Structural CharacteristicsTropical Depression(“incipient disturbance” in the text)
Up to 17 m s-1 (<
34 kts)Disorganized convection; Individual thunderstorms; a closed circulation is unlikely
Tropical Storm18-32 m s-1 (34-63
kts)Increased convection and organization; typically a closed circulationHurricane
(also Typhoon or Cyclone)> 33 m s-1 (>
Increased symmetry; a “mature” system; includes key structural features, and well-defined primary and secondary circulations.Severe Tropical Cyclone(Major
Hurricane or Super Typhoon)>100 kts Major Hurricane>135
The most symmetric of TCs; a
n eye is likely to form near 100
; severe TC classification varies by basin.
/ Extratropical TransitionVariousIf a TC encounters land while in the tropics, the storm will decay.If a TC exits the tropics (becoming extratropical), it may decay or re-intensify as an extratropical system.
2. Necessary (but not sufficient) conditions for TC Formation
3. Upscale Development
4. Formation Mechanisms by RegionSlide8
Incipient Disturbance: Structure
Localized, convective cells form frequently in the tropics. As we’ve
environment is conducive to the formation of thunderstorms. Tropical Cyclones are not instantaneous.“Intermediate, weak disturbances” must form first“Intermediate” refers to scale and duration, while “weak” refers to intensity
Thunderstorms satisfy this requirementOrganize into tropical depressions/storms/hurricanesThe initial disturbance can be very asymmetric prior to TC formation.Must have necessary but not sufficient conditions for TCs to develop
SST > 26oC
Moist mid-tropospherePositive relative vorticity at low levels
Minimal vertical wind shear (deep shear < 10 m/s)DO THIS: View the movie clip beneath Fig. 8.28 in your text. The clip shows the evolution of temperature and precipitation through the lifecycle of a convective cell.
oCThe ocean provides heat (sensible heat flux) and moisture (latent heat flux) to the atmosphere immediately above the surface of the ocean.This warm air right above the surface is then less dense than the surrounding air, and therefore rises – releasing the latent heat as the parcel cools and the moisture condenses into clouds
Moist mid-troposphereTall towers of deep convective clouds will only develop if moisture extends vertically into the atmosphere. If rising warm, moist air from just above the sea surface runs into a layer of dry air (such as the Saharan Air Layer), the lapse rate will change (from moist to dry) and the parcel will be much more apt to become neutral (i.e. and stop rising) or stable (and sink), and the convection will cease. However, if the column is moist, parcels will still continue to rise developing deep towers of spinning the atmosphere.
Positive relative vorticity at low levelsThis circulation (CCW in the NH) is indicative of an area of low pressure and is conducive to formation for two reasons:1. There will be convergence into the low that results in upward vertical motion and convection (as long as moisture remains in the column).
2. The vorticity allows the individual convective towers to merge as they spin inward (slightly) toward the center, forming a ring of convection around the low pressure center. Minimal vertical wind shear (deep shear < 10 m/s)
Strong TCs are symmetric horizontally and they are stacked verticallyHorizontal: Think of the “fat tire” or “donut” appearance of a strong hurricane or typhoon from a satellite perspective. The eyewall is evident as a thick ring of bright white (i.e. very tall) clouds, indicating very deep convection,. Winds here are also nearly symmetric about the storm center.
Vertical: The storm stands upright, and the strongest winds exist at the surface. . In regions of vertical wind shear, upper-level and lower-level winds are not identical. They can be different speeds, different directions, or both. Frequently, the upper-level winds are faster than the lower-level winds and the storm tilts over. The vertical integrity of the vertical columns is then disrupted and the columns dry out, reducing nearby convection.
* All conditions must be present simultaneously before tropical cyclogenesis can occur; HOWEVER, even if they are all present simultaneously, tropical
cyclogenesis may not occur…
(from Gray 1969)Slide10
TC Development: An “Upscale” Process
Deep thunderstorms are often
hot towers” to denote the latent heat released, which warms the column –or–
“vortical hot towers” (VHTs) to denote the cyclonic rotation present within the tower.These “incipient disturbances” must grow in size (spatial scale) and duration (temporal scale) in order to become a tropical storm.
The VHTs are convective scale systems, and to grow, they will often merge with larger mesoscale
systems MCV: mesoscale convective vortexMCS: mesoscale convective systemThis upscale growth continues through a process called “
axisymmetrization”denotes convection becoming symmetric about the center of a low-pressure system, which eventually becomes the vertical axis of the TCConvection that occurs on larger spatial scales will have longer temporal scales.
Thunderstorms can last several hoursHurricanes can last several days
(from Houze 2010)Slide11
Formation Mechanisms by Region
African Easterly Waves:
local convection and mesoscale systems that initiate in western Africa, subtropical cyclones.
Convergence upstream (east) of the trough axis results in convection.
Eastern PacificInstabilities in the ITCZ with moist easterly and equatorial waves originating from the Atlantic.West Pacific & Indian Ocean Monsoon trough, equatorial Rossby and mixed Rossby gravity waves, and merger of a number of small mesoscale systems.
) is a measure of the resistance of a symmetric vortex to “
forcings” acting to change its structure
Note: we said that a TS is “self-sustaining”, meaning that it was able to continue to develop even if one or more of the necessary (but not sufficient) conditions was lacking.The question is then: How can we quantify this?The formula for inertial stability is shown at right.Note the following relationships:
Inertial stability will increase when: relative vorticity,
Coriolis parameter, and
wind speed increaser decreases
(smaller radii, i.e. closer to the TC center).For a given radius and latitude (constant r and f):As wind speed increases, the inertial stability at that location increases.We expect inertial stability to vary with location in the TC.
is inertial stability
is the relative vorticity
is the local Coriolis parameter
The subscript denotes that the value is a constant and is derived from the TC center location
Winds are driven by the PGF between the systems (the TC,
pattern & STR).
Remember, the tighter the gradient, the faster the winds.
While it is convenient to look at pressure systems on the surface chart like the one above, TCs are steered by winds on more than just one level. In fact, the dominant steering level is 500 mb (~18,000’). Challenging aspect: At every level except the surface, forecasters look at constant-pressure charts (i.e. 300, 500, and 850-mb charts) to determine winds (and other weather features).
Since the entire chart is one pressure (i.e. 500 mb), contours on the chart mark the height of that surface. Higher heights indicate that the pressure surface (500 mb) is located higher in the atmosphere.RIDGE
think of a mountain on a topography mapLower heights indicate that pressure surface (500 mb) is located lower in the atmosphere.TROUGH think of a valley on a topography map
in the northern hemisphere than in the southern hemisphere.
In the southern hemisphere
, the polar jet is much more zonal (E/W). This strong westerly wind constrains the poleward extent of the TC track. (The jet is an upper-level feature and will shear the TC apart).In the northern hemisphere, the increased land mass creates greater thermal discontinuities, resulting in greater variability in the path of the jet. There is greater
meridional (N/S) flow which often facilitates increased poleward motion by TC exiting the tropics.
Landfall Changes in storm environmentLoss of ocean energy sourceWith less moisture, there is reduced convection; With reduced convection, there is less subsidence in the eyeThis weakens the warm core and raises the central pressure
This leads to a reduced pressure gradient and reduced surface windsIncreased frictionEffects on storm structureWeakening of surface winds
Redistribution of precipitation Go:
TC Exits the TropicsTC will undergo “Extratropical Transition”: Interaction with the Polar Front Jet will impact the symmetry of the TC.Vertical Wind Shear will cause upper levels to tilt eastward
Often this will destroy the coherence of the TC, and it will decay.Occasionally, however, the wave train will be positioned in such a way that the TC is absorbed and actually intensifies as an extratropical system.Decay: can result from the same “hostile” environmental factors noted for systems that remain in the tropics.
Intensification: If TCs evolve into extratropical systems, typically: symmetry decreasesDry air is wrapped into the southwestern sidePrecipitation increases on the northerneaster