Other Techniques for Investigating Hurricanes
Forecasters have developed various ways to gather and analyze tropical cyclones. Before the 1940s, the main source of information on these massive storms came from reports from ships because tropical cyclones form and spend most of their duration over water.
One of the original methods of gathering information was through manned aircraft. Of course, flying a plane with a human pilot into a storm is not a safe way to collect weather information. Hurricane Hunters, the aircrews who flew routine weather reconnaissance tracks, lost seven of their coworkers on October 1, 1945 when the plane went down a Category 1 typhoon.
As technology has advanced, researchers have gained access to aircraft reconnaissance, low-earth orbiting satellites, and operational geostationary satellites. Satellites revolutionized many aspects of meteorology. TIROS I was the first successful low-earth orbital weather satellite, launched in 1960. After this advancement, a great deal of research was done to find methods of analyzing the tropical cyclones’ intensity based on the satellite imagery.
One of the most successful methods of data collection, developed almost a decade later, is the Dvorak technique. Simply put, this technique analyzes the intensity of a tropical cyclone based on the evolution of its cloud patterns. Although many improvements of the Dvorak technique have been developed over the years, the technique has some limitations and suffers from the subjective nature of judgments about the cloud patterns.
The IR images of Hurricane Linda and the corresponding Dvorak intensities denoted by T2, T4, T6, and T8. Image courtesy of Colorado State University (PDF).
Satellites cannot give us precise and direct information about the interior barometric pressure of a hurricane nor the wind speed near the center of the storm. This information about the center of a storm, called the eye (shown in the following figure), is vital for forecasters to estimate the development, movement, and the intensity of a tropical cyclone.
Because satellites can't provide some of this pivotal information, other methods of data gathering were needed. Dropsondes and drones are two methods investigated over recent years for the direct measurement of more parameters.
The eye of Hurricane Isabel, 2003. Image courtesy of Mike Trenchard, Earth Sciences & Image Analysis Laboratory, Johnson Space Center.
A dropsonde is an expendable device which can accurately measure pressure, temperature, and humidity. Incorporating a GPS module, a dropsonde can measure the wind speed and direction based on how much the wind moves the device.
An aircraft is used to carry the sonde and drop it in a desired location. The readings of the sonde are transmitted to a computer in the aircraft. Immediately after being released, the dropsonde utilizes a small parachute to have a slow and stable descent. Moreover, the parachute keeps damage to the devices minimal as they strike the ground or the ocean.
In a typical hurricane season, Hurricane Hunters deploys 1000 to 1500 dropsondes. The following figure illustrates some of the most important features of a dropsonde.
The main features of a dropsonde. Image courtesy of NASA.
A dropsonde used in NASA's explorations. Image courtesy of NASA.
Global Hawk Tracking Hurricane Matthew
This year, a Category 5 Atlantic hurricane, dubbed Hurricane Matthew, left an alarming amount of damage in its wake. It killed over 1,000 people and left over 1 million people in Florida without power. While NASA flew planes with human pilots to gather information about Hurricanes Emily and Dennis in 2005, it instead employed a reconnaissance drone to observe Hurricane Matthew. This drone is called a Global Hawk.
The huge drone was sent over the hurricane to measure weather data such as temperature, air pressure, humidity, wind speed, and wind direction. To provide the real-time data, the drone released several dropsondes over the hurricane. The data captured by the dropsondes were transmitted to the National Hurricane Center in Florida, the National Oceanic and Atmospheric Administration, and other worldwide organizations that forecast weather.
Global Hawk, which is originally an unmanned surveillance aircraft for military applications, employs high-resolution radar and long-range infrared sensors to provide a broad overview and systematic surveillance of storm systems. The drone was estimated to cost about $222.7 million in 2013. It has a wingspan of 140 feet, weighs 15,000 pounds, and can fly over 30 hours at an altitude of 60,000 feet.
In December 2007, two Global Hawks were transferred from the U.S. Air Force to NASA’s Armstrong Flight Research Center at Edwards Air Force Base. To support applications similar to the Hurricane Matthew mission, the drone was equipped with weather sensors such as Ku-band radar, lightning sensors, and dropsondes. Before Hurricane Matthew, NASA successfully had flown the drone into Hurricane Earl on September 2nd, 2010.
NASA's Global Hawk drone. Image courtesy of NASA.
A Drone in the Eye of the Storm
In addition to the expensive Global Hawk, another aircraft, called Coyote, was dispatched by the National Oceanic and Atmospheric Administration (NOAA). However, unlike the Global Hawk which flew over the hurricane, the 13-pound Coyote drone was sent right into the eye of the hurricane.
The Coyote, which has a wingspan of five feet, was dispatched from a NOAA aircraft. A remote-controller steered the light-weight drone in different directions and guided it to the desired location in the storm. When prototyping in 2014, the drone was operated from only three miles away; however, in this recent mission, the signal range was increased to over 50 miles.
Coyote has many unique features. It can go to the lowest level of the hurricane, which is about 100 feet above the ocean, and give us an understanding of how the ocean affects the storm. According to Joe Cione, a meteorologist from the Hurricane Research Division (HRD), this information is sort of the Holy Grail for studying hurricanes.
Moreover, Coyote is equipped with infrared sensors to measure the temperature of the ocean’s surface.
In comparison with the $800 dropsondes used by the Global Hawk, the tiny $22,000 Coyote drone seems expensive. We should note, however, that in each mission of Global Hawk, several sondes need to be ejected. Therefore, the cost difference between using Coyote and ejecting dropsondes from the Global Hawk is not that much.
To have a fair comparison between the two methods, Cione notes that the descent of a dropsonde lasts less than five minutes while Coyote can fly for about an hour. As a result, the cost of data per minute is currently around $360 for a dropsonde versus $180 for a Coyote flight.
Learning more about tropical cyclones is pivotal in anticipating when and where the storms will form and where they will make landfall. This information would help coastal communities prepare more effectively for these devastating natural disasters.
With these successful strides in developing research methods, we can expect that the drones will increasingly prove to be more indispensable in meteorology. Due to the technological advancements these drones represent, more people—both in the Hurricane Hunters and in the path of a hurricane—will survive.