Hurricane

Atmospheric Phenomenon

WHAT IS A HURRICANE?

Hurricanes, or tropical cyclones, are large rotating storm systems with low pressure centers and high winds that typically last from several days to slightly more than a week. Only when the maximum sustained wind speed reaches 119 kilometers per hour (74 miles per hour) do we refer to these storms as hurricanes.  The term “hurricane” refers to tropical cyclones that forms in the North Atlantic and Eastern Pacific ocean basins, however, in other areas of the world hurricanes are referred to as “typhoons”, “tropical cyclones”, and “cyclones”.  Due to the effect of Earth’s rotation, hurricanes rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. The Saffir-Simpson Hurricane Wind Scale is commonly used to categorize hurricane strength into five categories based on each hurricane’s maximum sustained winds, which are representative of potential structural wind damage.  Hurricanes also cause a number of other hazards including heavy rainfall, high waves, rip currents, flooding, storm surge, tornadoes, high winds, landslides and lightning.

Image Source: UCAR The COMET Program


 

Why do hurricanes occur?

Hurricanes occur in the tropics and subtropics where there is warm, moist air and a low pressure disturbance causing air to converge and rise.  Near the equator, hurricanes cannot form due to the lack of the Coriolis force needed for storms to rotate.  In the Atlantic Ocean, most hurricanes form from easterly waves, or troughs of low pressure that originate over Africa. Through surface evaporation, warm sea surface temperatures serve as the main fuel source for hurricane formation.  Easterly waves force warm, moist air to rise, creating clouds and thunderstorms.  As the warm, moist air rises and produces clouds and precipitation, it releases latent heat through condensation of the rising water vapor molecules. This release of latent heat causes warming aloft making the air pressure higher and causing air to move outwards, or diverge away from the storm.  This, in turn, causes the surface pressure to lower, enhancing convergence of air into the storm at the surface, increased evaporation, rotation, and wind speeds.  Once the peak wind speeds reach 119 kilometers per hour (74 miles per hour), a hurricane is formed.  Hurricanes require deep, warm ocean water as an energy source and low wind shear (change of wind speed and direction with height) to enable storms to grow without being torn apart. The environmental conditions surrounding a hurricane determine whether it will continue to strengthen or weaken.  High wind shear, dry air, land, and cool water all prevent hurricane formation and can weaken existing storms.

Where do hurricanes occur?

Hurricanes (tropical cyclones) form within the Atlantic, Pacific, and Indian ocean basins in the tropics and subtropics, however, where they form within these basins is determined by the ocean currents, a pre-existing low pressure area, and the proximity to the equator.  As previously mentioned, hurricanes rarely form within 5 degrees of the equator due to the lack of Coriolis force.  In the South Atlantic and southeastern Pacific oceans, hurricanes do not form because the ocean currents in these areas transport cooler polar water towards the equator, failing to provide the source of fuel needed for hurricanes to form.  Once a hurricane forms in the tropical and subtropical regions of these ocean basins, they travel northward/southward into the midlatitudes where they weaken as they move over land and cooler ocean waters.

ASSOCIATED PHENOMENON

Flood

Storm Surge

Waves

Tornadoes

Lightning

HOW ARE HURRICANES OBSERVED?

Many spaceborne, airborne, and ground- and ocean-based instruments are used to monitor hurricanes.  Spaceborne satellites retrieve information needed to track and understand hurricane evolution and intensity, particularly the rainfall occurring within the storm, and the environmental conditions surrounding the hurricane.  This information helps inform forecasters who use it with numerical forecast models to predict the future path and strength of the storm.  Aircraft instruments are flown into hurricanes to acquire detailed measurements needed to better understand underlying processes that govern the size and intensity of a hurricane.  Instruments at sea situated on buoys and ships provide information about ocean and atmospheric conditions.  Ground-based measurements offer information on how intense the precipitation, atmospheric pressure, and wind speeds of the hurricane are.  Weather radars are used to observe rainfall in hurricanes, however, many are unable to be used until the storm nears landfall, given that they are located on land.

To better understand how hurricanes form, strengthen, and weaken, scientists conduct research projects using many different types of aircraft-, satellite-, and ground-based instruments.

 

GHRC Projects Containing Data used to Study Hurricanes

 

PROJECT RELEVANT INSTRUMENTS PLATFORM TYPE HOW WERE THESE DATA USED?
Camex-1, 2, 3, 4
Radar
Ceilometer
Lidar
AMPR
GOES-8
Field Mill
Hygrometer
Cloud Physics
AMPR
Rawindsondes
Radiosondes
Aerosonde
Dropsonde
MTP
Microwave Profiling Radiometer
SODAR
AERI
HAMSR
SAW
MAMS
Absorption Ozone Photometer
Doppler Wind Profiler

Airborne

 

Ground-based

Understanding hurricane development,

tracking, intensification, and landfalling

impacts

GRIP

HIWRAP

HIRAD

LIP

HAMSR

DAWN

Dropsonde

APR-2

GEOS-11,13

GHIS

Radiosonde

Cloud Microphysics

Lidar

Airborne

 

Spaceborne

Understand the formation and development

of tropical storms into major hurricanes.

HS3
HIWRAP
HIRAD
AVAPS
CPL
WWLLN
HAMSR
S-HIS

Airborne

Tropical cyclone development
Electric field measurements
Electrical structure of storms
Total lightning
Electric charge
Air conductivity
LANCE AMSR-2

Spaceborne

Provides low-latency data products

to observe hurricanes.

TCPF
GEOS 11
Aerosonde
CRS
HAMSR
Doppler Radar
MTP
LIP
Ticosonde

Ground-based

 

Spaceborne

Tropical cyclone structure, genesis, intensity
change, moisture fields and rainfall.
 
Satellite and aircraft remote sensor data
assimilation and validation studies pertaining to
development of tropical cyclones.
 
The role of upper tropospheric/lower
stratospheric processes governing tropical
cyclone outflow, the response of wave
disturbances to deep convection and the
evolution of the upper level warm core.
SANDS MODIS

Spaceborne

Sediment redistribution after hurricanes.

 

 

RESEARCH AND APPLICATION AREAS

Relevant Publications
Climatology
Landsea, C. W. (1993). A climatology of intense (or major) Atlantic hurricanes. Monthly Weather Review, 121(6), 1703-1713. https://doi.org/10.1175/1520-0493(1993)121<1703:ACOIMA>2.0.CO;2
 
Zhao, M., Held, I. M., Lin, S. J., & Vecchi, G. A. (2009). Simulations of global hurricane climatology, interannual variability, and response to global warming using a 50-km resolution GCM. Journal of Climate, 22(24), 6653-6678. https://doi.org/10.1175/2009JCLI3049.1
 
Physical Processes
Braun, S. A., Kakar, R., Zipser, E., Heymsfield, G., Albers, C., Brown, S., ... & Ismail, S. (2013). NASA's Genesis and Rapid Intensification Processes (GRIP) field experiment. Bulletin of the American Meteorological Society, 94(3), 345-363. https://doi.org/10.1175/BAMS-D-11-00232.1
 
Braun, S. A., Newman, P. A., & Heymsfield, G. M. (2016). NASA’s Hurricane and Severe Storm Sentinel (HS3) Investigation. Bulletin of the American Meteorological Society, 97(11), 2085-2102. https://doi.org/10.1175/BAMS-D-15-00186.1
 
Halverson, J., Black, M., Rogers, R., Braun, S., Heymsfield, G., Cecil, D., ... & McFarquhar, G. (2007). NASA's Tropical Cloud Systems and Processes Experiment: Investigating tropical cyclogenesis and hurricane intensity change. Bulletin of the American Meteorological Society, 88(6), 867-882. https://doi.org/10.1175/BAMS-88-6-867
 
Heymsfield, G. M., Halverson, J. B., Simpson, J., Tian, L., & Bui, T. P. (2001). ER-2 Doppler radar investigations of the eyewall of Hurricane Bonnie during the Convection and Moisture Experiment-3. Journal of Applied Meteorology, 40(8), 1310-1330. https://doi.org/10.1175/1520-0450(2001)040<1310:EDRIOT>2.0.CO;2
 
Kamineni, R., & Krishnamurti, T. N. S. Pattnaik, EV Browell, S. Ismail, and RA Ferrare, 2006: Impact of CAMEX-4 datasets for hurricane forecasts using a global model. J. Atmos. Sci, 63, 151-174. https://doi.org/10.1175/JAS3588.1
 
Modeling and Simulation
Holland, G. J. (1980). An analytic model of the wind and pressure profiles in hurricanes. Monthly weather review, 108(8), 1212-1218. https://doi.org/10.1175/1520-0493(1980)108<1212:AAMOTW>2.0.CO;2
 
General Information
 
DATE UPDATED
Apr 4th, 2018
AUTHOR(S)
Amanda Weigel
MICRO ARTICLE TYPE
Phenemonon

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