402 Flashcards
Tropical cyclone
- Warm core, low pressure system without any front
- develops over tropical or subtropical waters, has organized circulation
- Atlantic/eastern provinces - hurricanes
- Western pacific - typhoons
- Indian Ocean - cyclones
Hurricane
- low pressure system of tropical origin which generally moves into the mid latitudes and may move far enough into north america to affect the weather in Canada
Tropical meteorology
-the study of the atmosphere on the equatorial side of the subtropical highs
Why is tropical theory and forecasting different from extra tropical theory
- Small value of the coriolis parameter
- the high air temperature allows the air to hold large amounts of water vapour/energy
- The strong surface heating of the air, which produces a deep surface based conditional unstable layer
Difference between tropical and extra tropical weather:
Thermal advection and fronts
- Thermal advection is weak
- fronts do not exist
Difference between tropical and extra tropical weather:
Surface convergence
-slightest lifting of the air due to convergence will trigger the instability, which will be enhanced by release of latent heat during condensation.
Difference between tropical and extra tropical weather:
Upper level flow
- Easterly flow in both hemispheres
- tropical storms move towards the west, as opposed to westerly flow of extra tropical regions
Difference between tropical and extra tropical weather:
General Circulation
- weak circulation in the tropics
- westerly flow
Hurricane season in:
Atlantic, Caribbean and gulf of mexico
Pacific
- June 1 through November 30
- Maximum activity in September
May 15 - November 30
The main energy sources involved in the formation of hurricanes:
- WAA - almost Nil
- Diabatic heating - very little heat transfer as ocean and surface air temp are about the same
- Divergence - weak circulation
- Latent heat release - hurricane yeilds one million tonnes of precipitation per second
- ———–latent heat released during condensation warms the air sufficiently to lower surface pressure enough by the amounts observed
2 sources of energy at work during formation of hurricanes:
-Sensible heat - warm ocean transfers sensible heat to the air just above it.
Latent heat
Conditions that assist in
-Water vapour condensing warms the air, lowers pressure
- Intense latent heating, heats the column of air near centre of the storm - divergence aloft lowers surface pressure
- lower surface pressure - stronger surface winds
- Stronger winds increases friction via choppy seas
- stronger convergence into storms centre
- enhanced convection, cycle restarts
- positive feedback loop
6 elements required for the formation of a hurricane
- Latitude
- Over ocean
- positive low level vorticity
- conditional instability
- mid tropospheric humidity
- minimum vertical shear
6 elements required for the formation of a hurricane:
Latitude
- wind acceleration is latitude dependent
- Coriolis is of primary importance to induce and sustain cyclonic circulation
- 1-15 degrees of equator
6 elements required for the formation of a hurricane:
Over ocean
- Threshold sea-surface temperature of 26.5c below which tropical cyclones do not form
- inner region consumes huge amounts of sensiblle energy, affecting sea temperatures down to as deep as 60 meters
Positive low level vorticity
- tropical cyclone form only in regions of positive low-level positive vorticity, concentrated within 240 km
- convergence produces an increase of relative vorticity
Conditional instability
- conditional instability allows air parcel to continue to gain energy , until it is triggered to lift and all the energy is released at once
- can promote deep convection and aid in hurricane formation
mid tropospheric humidity
- seasonally averaged of mid level humidity must be high
- supports continuous convection
Minimum vertical shear
-prevents energy from being dispersed and allows for the enhancement of convective currents
