05/06/2016 Juma Al-Maskari, 1 Tropical Cyclones

2 What are Tropical Cyclones (TC) ? A low-pressure weather system in which the central core is warmer than the surrounding atmosphere. For this reason they are classified as “warm core” systems. They are also called Hurricanes, Typhoons.

3   Forms over a tropical ocean.   Center of storm is warmer than the surrounding air.   Has no fronts.   Strongest winds are near the Earth's surface.   Main energy source is the latent heat of condensation   Air sinks at the center of a TC   They are moved by steering winds in the troposphere.   TC weaken rapidly over land What are Tropical Cyclones (TC) ?

4 How do they develop ?   Warm ocean surface (T sea >26.5 o C) to a depth of ~ 50 m (evaporation)   Surface low pressure (convergence)   Surface winds are strongly cyclonic weakens with height   Moist air rises  condenses into water droplets and rain (latent heat released)  higher wind speed (mechanical energy)   Faster winds and lower pressure associated with them  increase evaporation and more condensation   Released energy increases updrafts   Divergence at upper levels   Weak vertical shear   Earth rotation (Coriolis force) causes the system to spin

5 Map of Tropical Cyclones © Wikipedia

6 Anatomy of a TC   The Eye   The Eye-wall   Rain-bands   Storm surge   Landfall

7 Anatomy of a TC

Airflow Patterns

14   The Eye: The low pressure centre of a tropical cyclone. Winds are normally calm and sometimes the sky clears. The eye of a storm is a roughly circular area and typically km in diameter. It is surrounded by the eyewall   The Eye-wall: The ring of thunderstorms that surrounds a storm’s eye. The heaviest rain, strongest winds and worst turbulence are normally in the eye wall. Anatomy of a TC

15   Storm Surge: is enhanced by high winds and greater storm size.   Rainbands : Rainbands are bands of showers and thunderstorms that spiral cyclonically toward the storm center.   Landfall: Officially, landfall is when a storm's center (the center of its circulation, not its edge) crosses the coastline. Anatomy of a TC

16 Classification   Low Pressure   Tropical Depression   Tropical Storm   Tropical Cyclone

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18 Categories/Classification

19 Why do we need to name TC ? Storms were initially given names to eliminate confusion when there are multiple systems in any individual basin at the same time which assist in warning people of the coming storm

20 Gonu meaning 'bag made from palm leaves' in Dhivehi, the Maldivian language. The name was one of the Maldivian contribution to the Panel on Tropical Cyclones Is Gonu an Indian Goddess ?

21 Frequency of Cyclones in Arabian Sea Juma Al-Maskari

22 Formation probability Juma Al-Maskari

Tropical (Cyclone) Applications of Satellite Data

One of first and most important applications of satellite observations in the tropics is the estimation of tropical cyclone position and intensity. 05/06/2016 Juma Al-Maskari, 24 Application: Intensity and position

Application: Track Forecasting Initial position/storm structure analysis Improvement of numerical models Assimilation of satellite data “Evaluation” of numerical models Synoptic feature identification for qualitative prediction Model analysis/satellite loop overlays provide assessment of t=0 hr accuracy 25

Application: Center Fixing Accurate positions necessary for estimation of storm motion Animation of imagery Visible/IR during day GOES IR window and shortwave IR at night Microwave imagery (SSM/I and AMSU-B) Formal center fixes began in

27 Forecast models, increased understanding of the forces that act on TC, as well as wealth of data from satellites and other sensors  lead to increase the accuracy of track forecasts. Accurate track predication depend on determining the position and strength of high and low-pressure areas, and Predicting how those areas will change during the life of a tropical system. However, prediction of TC intensity is still a challenge due to the complexity and incomplete understanding of factors that affect the development of these systems. How are they forecasted ?

28 HIRS sounder radiances AMSU-A sounder radiances AMSU-B sounder radiances GOES sounder radiances GOES, Meteosat, GMS winds GOES precipitation rate SSM/I precipitation rates TRMM precipitation rates SSM/I ocean surface wind speeds ERS-2 ocean surface wind vectors COSMIC data WindSat Quikscat ocean surface wind vectors AVHRR SST AVHRR vegetation fraction AVHRR surface type Multi-satellite snow cover Multi-satellite sea ice SBUV/2 ozone profile and total ozone Altimeter sea level observations (ocean data assimilation) AIRS MODIS Winds … Satellite Data Used in NWP

29 AMSUA/B, HIRS, AIRS DMSP SSM/I Scatterometers GEOS Satellite WindsOzone Coverage of satellite observations used in NWP

Satellite data used in NCEP’s operational data assimilation systems MODIS IR and water vapor winds GMS, Meteosat, and GOES cloud drift IR and visible winds GOES water vapor cloud top winds SSM/I wind speeds SSM/I precipitation estimates TRMM TMI precipitation estimates NOAA-17 HIRS 1b radiances AQUA AIRS 1b radiances NOAA-15, NOAA-16, NOAA-18 and AQUA AMSU-A 1b radiance NOAA-15, -16, and -17 AMSU-B 1b radiances GOES-12 5x5 cloud cleared radiances NOAA-16 and -17 SBUV ozone profiles 30