Tropical Cyclones: When Nature Attacks!! AOSC 200 Tim Canty. Tropical Cyclone: African Easterly Jet

Transcription

1 Tropical Cyclones: When Nature Attacks!! AOSC 200 Tim Canty Class Web Site: Topics for today: Really powerful low pressure systems Lecture 25 Nov Tropical Disturbance: Tropical Cyclone: African Easterly Jet Mid-level, Easterly winds blowing off of the hot Sahara Saharan Air Layer age=11.4.0&type=text 2

2 Tropical Disturbance: Tropical weather system 100 to 300 nmi in diameter Originates in tropics or subtropics May be associated with perturbations in the wind field known as easterly waves. Fig 12-9 Weather A Concise Introduction 3 Tropical Disturbance: Tropical weather system 100 to 300 nmi in diameter Originates in tropics or subtropics May be associated with perturbations in the wind field known as easterly waves. 4

3 Tropical Disturbance: Tropical weather system 100 to 300 nmi in diameter Originates in tropics or subtropics May be associated with perturbations in the wind field known as easterly waves. Fig Weather A Concise Introduction 5 Tropical Depression: Maximum sustained surface wind speed up to 38 mph Depressions have a closed circulation Weak low pressure center ~1010 mb 6

4 Tropical Storm: Maximum sustained surface wind speed 39 mph to 73 mph Convection usually more concentrated near the center Outer rainfall organizing into distinct bands Central pressure ~1000 mb 7 Hurricane: Winds equal or exceed 74 mph Further designated by categories on Saffir-Simpson scale Central pressure can drop very low (Hurricane Wilma 882 mb) 8

5 Saffir-Simpson Scale 9 Recurvature: the C shaped path of Hurricanes Hurricanes track around the Bermuda High When they turn North, Westerly jet stream pushes hurricanes to North-East 10

6 Strongly affected by sea surface temperature Fig 8-32 Meteorology: Understanding the Atmosphere11 Tropical Cyclone: Role of SST Need SST greater than 26.5 C (found in the tropics) Evaporation increases quickly with rising temperature Latent heat provides energy to storm Fig 8-23 Meteorology: Understanding the Atmosphere12

7 Tropical Cyclone: Why no cyclones near the equator? Fig 8-23 Meteorology: Understanding the Atmosphere 13 Tropical Cyclone: End of the storm Tropical Cyclones Diminish when they move over cold ocean water move over land interact with aloft winds or pressure systems 14

8 Anatomy of a Hurricane Fig 11-2 Essentials of Meteorology 15 Anatomy of a Hurricane Fig 12-4 Weather A Concise Introduction 16

9 Anatomy of a Hurricane Fig 11-3 Essentials of Meteorology 17 Tropical Cyclone: Wind Damage Winds on the left side blow in the opposite direction as the hurricane is moving. Subtract the two speeds. Winds on the right side blow in the same direction as the hurricane is moving. Add the two speeds together. Hurricane winds can be increased or reduced along path Can spin off tornadoes Fig Essentials of Meteorology 18

10 Tropical Cyclone: Seawater Ocean water piles up in front of storm due to winds and low pressure 19 Tropical Cyclone: Rainfall Weather service had to add new colors to their figures 20

11 Hurricane Sandy 21 Hurricane Sandy Greene et al., Oceanography,