Atmospheric Disturbances Tropical Storms & Cyclones

Intro to Tropical Storms Storms are regional atmospheric disturbances. Storms have high winds and most have precipitation. 2 major categories of storms: Tropical cyclones occur in tropical regions (within Hadley cells) Extratropical cyclones occur in Ferrel cells and are winter weather disturbances. Both types of storms are cyclones which are rotating masses of low-pressure air.

Tropical Storms Around the Globe Atlantic - hurricanes Named from Caribbean god Huracan Western Pacific – typhoons – most common Named from the Chinese word for “great wind” Indian Ocean and Australia – cyclones South Atlantic - almost none

Tropical cyclone genesis areas and related storm tracks

Hurricane Formation Steps in the formation of hurricanes Tropical disturbance  Tropical depression Tropical storm -- winds greater than 37 mph Hurricane, Typhoon, Cyclone -- winds greater than 74 mph 5 categories from the Saffir-Simpson scale based on the hurricane wind speed

Classification of Tropical Cyclones V. Storms Classification of Tropical Cyclones

Tropical Cyclones form in one air mass Air mass-A large mass of air with nearly the same temperature, humidity, and density Tropical Cyclones form from the Trade Winds because they need a warm climate Latent heat-the heat required to convert something into a different state of matter (Ex. solid  liquid or vapor, liquid  vapor) without change of temperature.

How a Tropical Cyclone Forms Warm, humid air forms in great quantity only over a warm ocean. When hot, humid tropical air rises and expands, it cools and is unable to contain the moisture it held when warm. Rainfall begins. Tremendous energy is released as this moisture changes from water vapor  liquid.

V. Storms The dynamics of a tropical cyclone, showing the influence of the Coriolis effect. Note that the storm turns the “wrong” way (that is, counterclockwise) in the Northern Hemisphere, but for the “right” reasons.

Tropical cyclone structure Hurricane characteristics Sustained winds greater than 120 km/hr (74 mph) Average diameter = 600 km (350 mi) Central pressure = ~ 950 mb to 870 mb

V. Storms (b) How precipitation develops in an extra-tropical cyclone. These relationships between two contrasting air masses are responsible for nearly all the storms generated in the polar frontal zone and thus responsible for the high rainfall within these belts and the decreased salinities of surface waters below.

Vertical temperature profile across a hurricane Hurricane eye -- average diameter = 25 km (15 miles) -- area of descending air -- strongest winds in eye wall (clouds just outside eye) Hurricane eye

The double eye wall of Hurricane Emily Hurricane with a double eye wall (occurs near maximum strength) eye walls

Hot tower in Hurricane Rita A hot tower is a part of the eye wall that rises to great height (up to 36 km); it can indicate hurricane strengthening

Erratic hurricane path examples Hurricane paths are controlled by trade winds, upper air flow, air pressure systems and ocean temperatures; they can be quite erratic.

V. Storms The warmest waters (shown in orange) are the breeding grounds of tropical cyclones are shown as orange-shaded areas. The storms follow curving paths: First they move westward with the trade winds. Then they either die over land or turn eastward until they lose power over the cooler ocean of mid-latitudes.

Predominant Atlantic hurricane paths

How a Tropical Cyclone Dies Can lose power over cooler land Can lose power over cooler ocean mid-latitudes (in Ferrel Cells) curving farther north or farther south

V. Storms The Atlantic Hurricane Season of 2005 Was the Most Destructive Ever Recorded A record 28 tropical cyclones formed, and 15 of these became hurricanes. Three hurricanes reached category 5 strength. One of these was Hurricane Katrina, the most costly natural disaster to befall the United States. Another was Wilma, the most intense Atlantic hurricane ever seen.

V. Storms The Atlantic Hurricane Season of 2005 Was the Most Destructive Ever Recorded (cont’d.) The 2005 season was extraordinarily costly in lives and property: Total damage estimates exceed US$100 billion, and at least 1,777 dead. More than 1.5 million people were displaced, the greatest number since the Great Depression of the 1930s.

Hurricane Destruction and Fatalities are caused by several factors: Wind Heavy rain Tornadoes Storm surge-Rise in water level associated with pressure drop

Blown sand from Hurricane Katrina

Extratropical Cyclones Form between Two Air Masses V. Storms Extratropical Cyclones Form between Two Air Masses (a) The genesis and early development of an extratropical cyclone in the Northern Hemisphere

Extratropical Cyclones Don’t become hurricanes or typhoons, but they cause weather patterns Cause strong winds, huge waves, and rain/snow Can form nor’easters: big, cold, storms in the north causing heating bills to rise, less fishing & shipping, and destruction

Heat transfer of cyclones Tropical cyclones-are necessary to move large amount of heat from tropics to higher latitudes quickly (faster than convection) Extratropical cyclones-mix warmth from tropics with polar air to redistribute heat important to life on earth!

Review Video Severe Tropical Storms https://www.youtube.com/watch?v=SSx_gisp24w What are hurricanes, typhoons, and tropical cyclones?

Video Questions Indian Ocean storms are called what? Western Pacific storms are called what? Atlantic Ocean storms are called what? From where do hurricanes draw their energy? What 2 elements do hurricanes need to form around? What speed must air be spinning to be a category 1 hurricane? What is the most destructive category of hurricane? What is the clear zone in the center of the hurricane? What is a wall of seawater hitting land called?