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1

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

2

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

3

Tropical meteorology

-the study of the atmosphere on the equatorial side of the subtropical highs

4

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

5

Difference between tropical and extra tropical weather:
Thermal advection and fronts

-Thermal advection is weak
-fronts do not exist

6

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.

7

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

8

Difference between tropical and extra tropical weather:
General Circulation

-weak circulation in the tropics
-westerly flow

9

Hurricane season in:
Atlantic, Caribbean and gulf of mexico

Pacific

-June 1 through November 30
-Maximum activity in September

May 15 - November 30

10

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

11

2 sources of energy at work during formation of hurricanes:

-Sensible heat - warm ocean transfers sensible heat to the air just above it.

12

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

13

6 elements required for the formation of a hurricane

-Latitude
-Over ocean
-positive low level vorticity
-conditional instability
-mid tropospheric humidity
-minimum vertical shear

14

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

15

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

16

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

17

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

18

mid tropospheric humidity

-seasonally averaged of mid level humidity must be high
-supports continuous convection

19

Minimum vertical shear

-prevents energy from being dispersed and allows for the enhancement of convective currents