Hurricanes And Thunderstorms Hazards To Aviation

Published Date: 02 Nov 2017

Aviation meteorology

PEME1120

Hurricanes and thunderstorms – hazards to aviation.

Anatolij Oniscenko 200670783

5/4/2012

Aviation meteorology. Hurricanes and thunderstorms– hazards to aviation. Anatolij Oniscenko.20067083

Introduction.

To begin with thunderstorms are the crucial elements of the hurricanes . That is why it is really important to analyse the formation about them before describing hurricanes. "Thunderstorms generate spectacular weather which may be accompanied by thunder, lightning, heavy rain, squalls and tornadoes" (1). Each of these dangers can be difficult to handle with. However, if all these circumstances appear at once, they can be tragic. Understanding basic thunderstorm formation and arrangement can prevent pilots from doing severe mistakes, which may affect the safety of the flight. The Worldwatch Institute stated that in 2008 severe weather conditions caused more than 30000 deaths and up to $90 billion damage in infrastructure (2).Hurricanes usually destroy coastlines, tornadoes flow through the territories of the countries with a huge force, as well as annihilate crops and leave millions of people homeless (2).More than 40000 thunderstorms appear through the world each day (3). So what causes such a severe unstable weather conditions and may humanity reduce damage and consequences caused by storms?

Usually thunderstorms related to cumulonimbus clouds (1). Furthermore, it could be more than one thunderstorm sector or "cell" within the cloud (1). All kinds of thunderstorms represent a huge danger to aviation, especially to light and small aircrafts. Thunderstorms are divided into two particular types: ordinary and severe (3). The ordinary thunderstorms are typical summer storms and generally last approximately 60 minutes (3). The precipitation (form of water: rain, snow, sleet, or hail, that falls to the earth's surface) connected with these types of storms, usually comprises rain and sometimes slight hail (4). With ordinary thunderstorms, cumulonimbus clouds may raise up to 12 kilometres high (3). Severe thunderstorms are very hazardous (3). They are capable of creating baseball-sized hail, particularly very powerful winds, intense rain, flashy floods, and even tornadoes (3). Severe thunderstorms can last a number of hours and can raise 18 kilometres high (3). Several phenomena are related with severe thunderstorms, containing gust fronts, hurricanes, microbursts and the squall lines (3).

The three essential conditions for the thunderstorm formation.

For a thunderstorm to develop the three conditions are needed (1).It is a deep instability, high moisture content and a trigger action (1).

Moisture. Enough moisture content must be present in the atmosphere for clouds to start forming (5). Even though convection happens in the atmosphere without visible clouds, moisture is not the only source of visible clouds, but also a kind of "fuel" the convection to continue (5). As the warm air starts to rise, it begins to cool, and the water vapour in the atmosphere condenses into cloud droplets (5).

Deep instability. "So that one the air starts to raise it will continues rising (1)." Overall, as there is an increase in altitude, the air temperature refrigerates up to the top of the troposphere (5). A measure of atmospheric stability is the speed of the air cooling (5). Meteorologists denote to this vertical alteration in temperature as the lapse rate (5). The temperature generally decreases 1.98 °C per 1000 feet. If the actual climbing air cools slower than the lapse rate, the air remains relatively warm compared to the surrounds, so that is why it continues to rise (5).

Trigger action. Trigger action (also known as catalyst) , encourages the air, rising from : a front obliging the air aloft; a mountain forcing the air aloft; strong heating of the air in connection with the earth`s surface or heating of the lower layers of a polar air mass as it transfers to lower latitudes. (1).

The life Cycle of a Thunderstorm.

"Most thunderstorms form by a cycle that has three stages: the cumulus stage, mature stage, and dissipating stage (6)".

Figure 1. The three stages of the thunderstorm (5).

Cumulus stage. As the moist air starts to rise, the same time it begins to cool until it reaches its dewpoint temperature (1).After that the water vapour condenses in liquid droplets and the stage of the cloud formation begins (4). The rising air cools at a lesser rate as latent heat goes off in the condensation stage (4). At this initial phase in the formation of the thunderstorm, the strong and warm updraft occurs with a diameter approximately one or two miles (1). However, at this stage still there are no downdrafts, which usually appear it the late stages. Air causes the updraft to become stronger with height, as it is drawn horizontally inside the cell at all heights (1). The is a slight difference between the temperature inside and outside the cloud (4). It is higher inside the cloud comparatively to the temperature of the surround air (4). That makes cloud to rise to greater and greater height levels (1). Furthermore, the warm updrafts bring the water droplets to upper and upper levels of the cloud, where liquid droplet coalesce in order to form bigger drops (1).

http://www.physicalgeography.net/fundamentals/images/thunderstorm.jpg

Figure 2. The cumulus stage of the thunderstorm (7).

The mature stage. It is the stage, where the downdrafts appear. The duration of this phase is longer, as it usually takes from 20 to 40 minutes, whereas the cumulus stages takes only 10-20 minutes. The mechanism of the downdraft formation is quite simple. As the water droplets ultimately become too big and too heavy, they can not be supported by the coming updrafts (1). It means that the droplets start to fall, causing the drag of the air along their downfall trajectory in the cloud (1). Very often, the first lighting and rain appears particularly in the mature stage of the thunderstorm (1). The downdraft tugs the heavy water downward, causing rain or even hail (6). Such a cloud becomes a cumulonimbus, as it has an updraft, a downdraft, and rain (6). Eventually thunder and lightning start to follow, as well as heavy rain (6). After that the cumulonimbus cloud occasionally becomes a thunderstorm cell (6). The top of the cloud in this mature stage is different and depends on the latitude and even may reach tropopause (1). The most important feature of the thunderstorm, which allows recognising the mature stage of it, is the typical shape of a cumulonimbus with the top spreading out in an anvil shape in the direction of the wind (1).Furthermore, that stage is dangerous due to formation of the severe windshears. That could be explained as the cold downdrafts flow out of the base of the cloud and begin changing the direction (1).Consequently, the horizontal wind flow occurs, when the ground is approached (1). Moreover, the roll cloud may also develop at the base of the main cloud, in a place, where the cold downdrafts and warm updrafts pass through.

http://www.touringmachine.com/images/NOAA-Thunderstorm.jpg

Figure 3. The mature stage of the thunderstorm; formation of the anvil in the cumulonimbus cloud (8).

The dissipating stage. After about half an hour, the thunderstorm begins to dissipate (6). This happens when the downdrafts in the cloud begin to dominate over the updrafts (6). Subsequently the warm moist air can no longer rise, so cloud droplets can no longer be present inside of the cloud; that leads to the death of the storm (6). Usually, the storm ends with the light rain as the cloud dissolves from the bottom to the top (6). http://www.k3jae.com/images/storm-develop.png

Figure 4. All stages of the thunderstorm formation. (9).

Hurricanes.

"A hurricane is a type of tropical cyclone or severe tropical storm that forms in the southern Atlantic Ocean, Caribbean Sea, Gulf of Mexico, and in the eastern Pacific Ocean" (11). A typical cyclone is supplemented by thunderstorms and counter clockwise circulation of winds by the earth’s surface in Northern hemisphere (11). So as was mentioned earlier the tropical cyclone is a rotating, organised assembly of clouds and thunderstorms that originates over tropical and subtropical waters having relatively closed low-level circulation (13). The best definition for hurricane is a tropical cyclone with a maximum wind speed of 64 knots (13). In the western North Pacific they are called typhoons; analogous hurricanes in the Indian Ocean and South Pacific Ocean are named cyclones (13). The peak of Atlantic Ocean’s hurricane season start approximately in the middle of August to late October and averages five to six hurricanes per year (12). Hurricanes originate as tropical disturbances in warm ocean waters with surface temperatures of at least 26.5 degrees °C (12). A hurricane’s high winds are also very hazardous and destructive and even may give birth to tornadoes (12). Hurricanes are massive heat engines that produce energy on an astounding scale (12). They gain heat energy from the ocean via the heat of condensation from water vapour (with solar energy being the initial source of evaporation) and twist around a low-pressure centre known as the "eye" ,which is surrounded by a circular "eye wall" that engages the storm’s strongest winds and rain (12). A twist of the hurricane is driven by physical forces (rotation and gravity).However, hurricanes may also carry heat energy away from the tropics and transfer it away from high temperate latitudes, which makes them a very important part of the Earth`s atmospheric circulation mechanism. As a result, tropical cyclones help to keep equilibrium in the Earth's troposphere and maintain constant a relatively stable and warm temperature worldwide. Hurricanes could be extremely dangerous, as they can extend 100 miles.Peak Of Season

Figure 5.Number of Tropical Cyclones per 100 Years (13).

http://www.nhc.noaa.gov/climo/images/tcformation.png

Figure 6. Tropical Cyclone formation regions with mean tracks (13).

2012

2013

2014

2015

2016

2017

Alberto

Andrea

Arthur

Ana

Alex

Arlene

Beryl

Barry

Bertha

Bill

Bonnie

Bret

Chris

Chantal

Cristobal

Claudette

Colin

Cindy

Debby

Dorian

Dolly

Danny

Danielle

Don

Ernesto

Erin

Edouard

Erika

Earl

Emily

Florence

Fernand

Fay

Fred

Fiona

Franklin

Gordon

Gabrielle

Gonzalo

Grace

Gaston

Gert

Helene

Humberto

Hanna

Henri

Hermine

Harvey

Isaac

Ingrid

Isaias

Ida

Ian

Irma

Joyce

Jerry

Josephine

Joaquin

Julia

Jose

Kirk

Karen

Kyle

Kate

Karl

Katia

Leslie

Lorenzo

Laura

Larry

Lisa

Lee

Michael

Melissa

Marco

Mindy

Matthew

Maria

Nadine

Nestor

Nana

Nicholas

Nicole

Nate

Oscar

Olga

Omar

Odette

Otto

Ophelia

Patty

Pablo

Paulette

Peter

Paula

Philippe

Rafael

Rebekah

Rene

Rose

Richard

Rina

Sandy

Sebastien

Sally

Sam

Shary

Sean

Tony

Tanya

Teddy

Teresa

Tobias

Tammy

Valerie

Van

Vicky

Victor

Virginie

Vince

William

Wendy

Wilfred

Wanda

Walter

Whitney

Table 1. Since 1953, Atlantic tropical storms had been named from lists originated by the National Hurricane Centre (13).

Difficulties for aviation.

As the main elements of the hurricane are strong winds and thunderstorms, the particular hazards for aviation come from them. The only difference that hurricanes are much more powerful and widespread for long distances than separate thunderstorms. It is very important to know not only that danger could be not inside the hurricane but also for quite some distance around it. So the thunderstorms must be avoided at least 10 nm or in severe cases 20 nm (1). Thunderstorms are particularly dangerous for light aircrafts as they usually do not have whether radars. Firstly, damage from lighting strikes, not only mechanical but also including electrical damage such as interference to radio communications and radio navigation instruments (1).Large metal aircraft has good protection for the occupants, but contains sensible to a lighting strike electronic components (3).Wooden and GRP aircrafts could obtain a serious damage or even destruction from lighting (3). The main hazard from lighting is due its ability to strike along away from the cumulonimbus cloud (more than 10nm) (3).Secondly, reduced visibility could also be a severe problem for VFR aircrafts. Thirdly, severe icing (both rime and clear).All of them strongly affect lift, increase weight, cause additional drag and carburettor icing. As thunderstorms are driven from the conversion of liquid water to ice it is expected to find an airframe icing in all kind of thunderstorms (5). Although all forms of icing may appear during a flight trough thunderstorm clouds, clear icing, caused by larger drops of supercooled water, is the most appropriate form of icing (5). Another issue of icing during the flight via thunderstorms is pitot tube icing, which seriously affects the indication of the airspeed. Recent case was with the Air France 447 flight. It has been suggested that pitot tube icing may have been a contributing factor for the crash of Air France Flight 447 ,which was flying through the thunderstorm. The next very severe hazard of the thunderstorm is turbulence, which is able to cause loss of control and structural damage of the aircraft. Pilot reports from aircraft suffering from thunderstorm have noted up and down drafts exceeding 6000 feet per minute (5). Nevertheless, turbulence, which may exceed the performance capability of most aircraft, can be found inside and even around thunderstorms (5). It is very important not to forget about hail damage, which also could very severe. The most vulnerable parts of the aircraft for the hail are cockpit windows and the airframe. However, the most dangerous consequence of the thunderstorm and hurricane is severe windshear. It may cause flight path deviations, control problems, loss of airspeed and possibly structural destruction (1). "The passage of an aeroplane through the windshear of violent updrafts and downdrafts of the cumulonimbus clouds can result in structural failure" (1). Furthermore, the rapidly changing direction of the airflow, which strikes the airframe and the wings, could also cause a stall (1).

In conclusion, hurricanes and thunderstorms are extremely hazardous to aviation, so pilots have always to remember the following publication of the FAA - Weather Avoidance Tips. "To rely solely on Air Traffic Control (ATC) as a source for weather avoidance is not entirely prudent. It is the pilot’s responsibility to obtain a pre-flight weather briefing. Any ATC reported weather information, along with periodic contacts with Flight Watch while airborne, will supplement what was learned during the pre-flight briefing. The ATC reports of precipitation areas are of value because they can give you a global view of what is in the area (14)."