Hurricanes: Description and Scientific Analysis

Introduction

Records of hurricanes have existed since before modern society. Hurricanes are defined by their strong winds and torrential rain. Scientists have developed new methods and techniques that attempt to forecast the intensity of hurricane threats. Hurricanes like Camille, Andrew, and Hurricane Katrina have ravaged the Gulf Coast prompting more research into the predictability and response for hurricane disasters. This paper will contain four elements about hurricanes which include a general overview, methods of study and tools used, discoveries, and unanswered questions.

General Overview

The National Oceanic and Atmospheric Administration's Hurricane Research Division states that hurricane is a specific term used to refer to a tropical cyclone that forms in the tropical waters of the North Atlantic and must have minimum wind speed at 74 mph (Landsea 2011). Scientists hypothesize that hurricanes are caused by easterly waves that form off the coast of Africa. Dunkerton, Montgomery, and Wang (2009) observe that easterly waves are, “A prominent synoptic-scale feature of the summer tropics, centered ten or more degrees off the equator just poleward of the ITCZ [Intertropical Convergence Zone], originating and propagating westward across tropical Africa, the tropical Atlantic, and eastern or central tropical Pacific,” (p. 5639). Easterly waves are caused by the warm temperatures of the Saharan desert that come into contact with cool temperatures off of the coast of Guinea. This causes the easterly jet to destabilize which breaks the air current into an easterly wave (Emanuel, 2005, p. 98). Hurricanes depend upon the convection that occurs in the warm waters of the Atlantic because warm temperatures fuel the organization of the storm. The NOAA website further summarizes that the formation of a hurricane depends on water temperatures of at least 80 degrees Fahrenheit with moist levels of air in the middle of the system with a decent level of vorticity or spinning motion. For a hurricane to gain momentum the Coriolis Effect caused by the Earth’s rotation must be present with low levels of vertical wind shear (Landsea, 2011). These factors represent the best hypothesis on the causation of hurricanes.

A hurricane is composed of the eye, the eyewall, winds, and storm surges. The eye is a somewhat circular center of the hurricane that experiences warmer temperatures, light winds, and little precipitation. The NOAA website provides a summary of the different hypotheses on how the eye is formed, “In either case, as the air subsides, it is compressed and warms relative to air at the same level outside the eye and thereby becomes locally buoyant. This upward buoyancy approximately balances the downward directed pressure gradient so that the actual subsidence is produced by a small residual force” (Landsea, 2011). A combination of wind direction and air temperature causes the conditions to form the eye structure which is surrounded by the eyewall defined by strong thunderstorm activity which results in high winds and heavy rains. Maximum sustained winds are defined by the NOAA as surface winds that are last for more than 1 minute, while gusts last only a few seconds. The storm surge represents an unusual amount of rise in the tide due to the hurricane which can cause massive amounts of flooding on the coast.

Methods of Study and Tools Used

Scientists use methods and tools to measure the different characteristics that determine the intensity of hurricanes and that help forecast their formation. One of the most prevalent methods of studying hurricanes utilizes hurricane reconnaissance aircraft. Kerry Emanuel (2005) describes the process of using these crafts, “...many reconnaissance flights deploy dropwindsondes, instrument packages on parachutes that float down to the sea surface, transmitting information back to the aircraft,” ( p. 200). These tools measure humidity, pressure, wind speed, and air temperature to provide data for computers to process about the hurricane’s track. Emanuel points out that scientists use Airborne Expendable Bathythermographs which are lowered from the aircraft with parachutes to determine ocean temperatures. Many aircraft are being replaced by unmanned aerial vehicles (UAV) to ensure the safety of scientists (201). Meteorologists also use satellites like the Tropical Rainfall Measuring Mission (TRMM) to measure rainfall (185). The NOAA website highlights some of their strategies for researching hurricanes which include the Doppler radar system which tracks the movement of hurricanes and the Saffir-Simpson Hurricane Wind Scale that measures the wind speed to predict damage (Landsea, 2011). Researching hurricanes requires technology that can accurately forecast the relatively unpredictable nature of these natural disasters.

New Discoveries

The National Science Foundation recently published an article that describes the Prediction Intensity Interval for Hurricanes model (PIIH). The model measures wind and, “...uses previous data, including current maximum intensity, the potential for an increase in intensity, time of year, various temperature measurements, the direction of storm movement and wind shear--the difference in wind speed and direction over a relatively short distance in the atmosphere,” (New forecasting, 2011). The PIIH depends on the statistics of past hurricanes to roughly determine the intensity of new hurricanes. The atmospheric conditions, when combined with the current time of year, are used to forecast the outcome of hurricanes that could make landfall along the coast.

Unanswered Questions

Even though scientists have relied on traditional meteorological techniques to forecast hurricanes, there is still much more progress to be made. Emanuel (2005) states that meteorologists need better instruments to measure the atmosphere as well as more accurate algorithms to improve models (p. 235). The author further implies that scientists are still unsure as to why hurricanes are triggered and why they do not occur more often (p. 95). He explains that scientists must increase understanding of how humidity develops in the mid-level of the atmosphere which is generally a precursor to a hurricane forming as well as investigating the complete process by which easterly waves become organized hurricanes (p. 96-98). The cause and formation of hurricanes remain the most unanswered aspect of these storms which prompts scientists to research more comprehensive tools of analysis.

Conclusion

Hurricanes have the potential to cause a substantial amount of damage depending on the intensity of their winds and storm surges. Scientists are constantly inventing new technologies to address the remaining challenges to understanding the formation and cause of hurricanes. The term hurricane is one of a few specific types of tropical cyclones that form within the Atlantic Ocean. One of the proposed causes of hurricanes consists of easterly waves becoming organized into storm fronts that feed on warm water and humidity. These storms evolve into hurricanes with identifiable eyes, the center of the hurricane with little activity, and eyewalls where most of the intense winds and rain happens. Scientists use several tools and methods to measure hurricanes including aircraft, satellites, and computer models to study hurricanes. The PIIH is a newly discovered algorithm that forecasts hurricanes based on maximum wind speed. Meteorologists are researching new ways to specify how hurricanes form which includes an overall emphasis on examining atmospheric conditions.

References

Emanuel, K. (2005). Divine Wind: The history and science of hurricanes. New York, NY: Oxford University Press.

Dunkerton, T. J., Montgomery, M. T., & Wang, Z. (2009). “Tropical cyclogenesis in a tropical wave critical layer: Easterly waves.” Atmospheric Chemistry & Physics, 9(15). Retrieved from file:///C:/Users/owner1234/Downloads/acp-9-5587-2009.pdf.

Landsea, C. (2011). Frequently Asked Questions. Retrieved April 14, 2014, from http://www.aoml.noaa.gov/hrd/tcfaq/A1.html.

New forecasting algorithm helps predict hurricane intensity and wind speed. (2011). Retrieved April 14, 2014, from http://www.nsf.gov/discoveries/disc_summ.jsp?cntn_id=122439.