Marit Finne Ed i t o r -i n -C h i e f Vai s ala New s Vai s ala Helsinki NOAA’s WP-3 Orion Hurricane Research Aircraf t are among the most Fi n l a n d advanced airborne environmental research platforms for the study of seve r e storms and global climate chan g e . NOAA ‘Hurricane‘Hurricane Hunters’Hunters’ Flying in the Storm

Specially equipped NOAA aircraft r o u n d b r e a king re- ously low altitudes. The ‘NOAA se a r c h and im p r o v - Hurricane Hunters’ Captain play an integral role in hurricane ed forecasts have al- David Tennesen and Lieuten- fo r e c a s t i n g . NOAA’s Hurricane G re a d y emerged from ant Commander Sean White Re s e a r c h Scientists fly a Gulfstream the data gathered by RD9 3 are NOAA Corps officers sta- G-IV Jet beyond hurricanes at high GP S dropwindsondes in hurri- tioned at the Aircraft Opera- canes and winter storms. The tions Center at MacDill Air altitudes (40,000–45,000 feet) and dropsonde data have improved Force Base in Tam p a , Florida. two WP-3 Orion turboprops into the mean hurricane track fore- Captain Ten n e s e n , a pilot since hurricanes at low altitudes casts from the Geophy s i c a l 1968, is the senior aviator at Fluid Dynamics Lab o r a t o ry ’ s AO C while Lieutenant Com- (1,5 0 0 – 1 0,000 feet), to collect (GF DL) hurricane model by as mander White, a meteorolo- re s e a r c h data. During their mu c h as 32 per cent and the gi s t , has been Project Manager mi s s i o n s , these aircraft release intensity forecasts by as much for the NOAA Gulfstream IV Vai s ala RD93 GPS dropwindsondes as 20 per cent.*) since its acquisition. Specially equipped NOAA used for weather reconnaissan c e , Pilots trained to aircraft play an integral role in hurricane and weather research. fly hurricanes hurricane forecasting. Data col- lected during hurricanes by NOAA Corps pilots, who sup- these high-flying meteorologi- po r t the civilian scientists and cal stations and from a variety engineering staff of the Aircraft of other sources are fed into Operations Center (AOC), are numerical computer models, to among an elite group of pilots help forecasters predict how who are trained to fly into hur- intense a hurricane can be, and ri c a n e s , sometimes at danger- where it will make landfall.

14 150/1999 Hurricanes Have a Mind of Their Own

Satellite images of hurricanes show a unique and characteris - tic cloud forma t i o n , signaling an intense tropical weather sys- te m . The powerful storms spawned in the tightly coiled sys- tems produce heavy rain and winds with maximum sustained sp e e ds of 74 mph/64 knots (33 m/s). The United States has a significant hurricane problem. There are already some 45 million permanent residents along The NOAA G-IV plane flies the hurricane-prone coastlines – and the population is still hi g h - altitude tracks, between gr o w i n g . 41,000 to 45,000 feet (12, 4 9 7 A hurricane is a type of tropical cyclone – a general term –13 , 716 m), to release the GPS for all weather systems circulating (counterclockwise in the dropsonde at predetermined No rt h e r n Hemisphere) over tropical waters. lo c a t i o n s . Using the specific Hu r r icanes are products of the tropical ocean and atmos- mission systems onboard the phere. Pow e r e d by heat from the sea, they are steered by the ai r c r a f t , the information meas- eas t e r ly trade winds and the temperate westerli e s , as well as ured by the GPS dropsonde is by their own ferocious energy. Around their core, winds grow co l l e c t e d , analyzed, processed, to a great velocity, generating violent seas . Moving ashore, formatted into a message and they sweep the ocean inward while spawning tornadoes and transmitted via Satellite Com- producing torrential rains and floods. Each year an average Lieutenant Commander Sea n munications (S ATCOM) to of ten tropical storms (of which six become hurricanes), deve l - White is Project Manager of the the ground, almost in real time. op over the Atlantic Ocean , Carib b e an Sea, or Gulf of NOAA Gulfstream G-IV Jet , seen These atmospheric vertical pro- Me x i c o . Every three year s , about five hurricanes strike the files are used to initialize in the bac kground with the Mup p e t s Un i t e d States coastline. Two of the five will be major hurri- numerical models providing char acter logo. canes (catego r y 3 or great e r , on the Saffir-Simpson Hurric a n e data otherwise not available in Scale. The scale from minimum to maximum is 1 to 5). the ’data void’ regions over the oc e a n s . Captain Tennesen say s , “Since NOAA’s Corps pilots fly the the 199 7 hurricane season, the Gulfstream G-IV Jet at high G-IV jet complements the work altitudes (41,000–45,000 feet) of the WP-3s. Data from drop- and two WP-3 Orion turboprops sondes measuring barometric at lower altitudes (1,5 0 0 – 2 5 , 0 0 0 pressure, temperature, humidi- fe e t ), to collect research-m i s - ty , and wind flow are transmitt- sion data. Lieutenant Com- ed to a satellite, which then mander White explains that he transmits the data to the Na- coordinates field operations tional Hurricane Center in Mia- and crew activities (pilots, mi , and the National Envi r o n - me t e o r o l o g i s t s , engineers and mental Satellite, Data and In- te ch n i c i a n s ) in all the phases re- formation Service outside Was h - quired to accomplish each mis- in g t o n , DC. ” si o n . Air missions DR93 GPS dropsonde relay storm data me asures critical atmospheric conditions During hurricane synoptic sur- veillance missions, the NOAA The Airborne Ver tical Atmos- G-IV flies in the envi r o n m e n t pheric Profiling System (AVAP S) of the hurricane. The tracks usu- was developed by the U. S. ally target specific areas around National Center for Atmos- the hurricane, concentrating on pheric Research (NCAR), in cooperation with the German PHOTO COURTESY OF NOAA, USA. Aerospace Research Establish- ment (DLR) and the NOAA Co r p s . NCAR has licensed the production of the RD93 GPS dropsonde, which is a key com- ponent of the AVAP S, to Vai - sal a . The Airborne Ver tical At- mospheric Profiling System, wh i c h incorporates a Vai sa l a RD93 GPS dropwindsonde, is Lieutenant Commander Sean White, with Vaisala’s DR93 GPS an advanced tool for weather Captain David Ten n e s e n , the Sen i o r Dropsonde, coordinates field operations and crew activities in all the re c o n n a i s s ance, hurricane and Av i a t o r , with his favorite aircraf t, ph ases required to accomplish each mission in the NOAA aircraf t. weather research. NOAA WP-3 Orion.

150/1999 15 synoptic features that influence This picture shows the lightning rod protruding from the front of the aircraf t. its track. For winter storm recon- *) Ref e r e n c e s na i s s ance, the aircraft flies in [1] Ho c k, Terrence F., and sensitive areas over the No rt h James L. Frankli n , 199 9 : Pacific two to five days upstream The GPS Dropsonde, The of the weather development areas Bulletin of the American affecting the United States. The s e Meteorological Society, predetermined sensitive areas Volume 80, No.3, are chosen to provide the nu- Ma r c h 199 9 . merical models with crucial data that otherwise would be [2 ] Ab e r s o n , Sim D. and James un a v a i l a b l e . L. Frankli n , 1999: During the acquisition pro- Impact on Hurricane Tra c k cess and instrumentation of the and Intensity Forecasts of NOAA G-IV, the Atmospheric GP S Dropwindsonde Tec hnology Division (ATD ) of Ob s e r vations from the the National Centers for Atmos- Fi r s t - Season Flights of the pheric Research was chosen to NOAA Gulfstream-IV Jet design and develop the new Ai r c r a f t , The Bulletin of GP S dropsonde. The NCAR / the American ATD chose Vai s ala’s PTU sen- Meteorological Society, sor and GPS components for Volume 80, No.3, their design of the new GPS Ma r c h 199 9 . dropsonde. “T hough I was only indirect- ly involved in the enhancement process that further improved be a success. This includes the the GPS dropsonde, I have dr o p s o n d e s . The accuracy of nothing but high praise for the Vai s ala instrument and the Vai s ala’s efforts to respond to information it collects directly our needs and the tight deliver y affects the weather forecasts for sc hedule. Along with individu- the entire No rthern Hemi- als within NOAA, NCAR and sp h e r e . ” the Air Force’s We a t h e r Lieutenant Commander White Re c o n n a i s s ance Squadron, Vai - says his most memorable expe- sala’s commitment to quality rience was a flight into Hur- has provided the GPS drop- ricane Hugo as the navigat o r sonde that will enable the on a WP-3 aircraft in Sep- NOAA G-IV to enter the 21s t tember 1989, during a mission Ce n t u r y as the premier high- originating from Barbados. altitude platform,” Sean White “During this low-level research say s . m i s s i o n, the aircraft experi- enced extreme turbulence upon Res e arch flying is entering the eyewall of Hur- a team effort ricane Hugo, at an altitude of Hurricane Hugo making landfal l , September 22, 198 9 . Charleston rad a r 1,500 feet (452 m). After a pre- The Aircraft Operations Center image. Photo courtesy of NOAA, Hurricane Research Division, USA. ca u t i o n a r y shutdown of one of (A O C) was created in 1983 to the engines during the eye-wa l l consolidate the aviation assets penetration and the subse- of the National Oceanic and quent entry of the calm eye at Atmospheric Ad m i n i s t r a t i o n. about 800 feet (243 m), the 3- Its versatile aircraft collect the engine, 1-hour climb to a saf e r en vironmental and geographic altitude in the small eye of data essential to NOAA hurri- Hu g o , together with the pene- cane research. “Our aircraft tration of the eyewall to exit operate in some of the world’s and the subsequent ferry back most remote and demanding to Barbados formed the most flight regimes – over open ocean, sobering experience of my life.” mountains and coastal wet- The center, or eye, of a hurri- la n d s , in and around hurricanes cane is relatively calm. The most or other severe weather,” Cap- violent activity takes place in the tain Tennesen points out. area immediately around the David Tennesen stresses that eye, called the eyewall. At the the research flying they do is top of the eyewall, (about ve r y much a team effort. “Eve r y 50,000 feet /15,240 m), most of crew member and the research The graph shows the vertical motion the NOAA Hurricane Hunters fly the air is propelled outward, in- instruments they operate must through on one of their research flights. As can be seen, this is not a smooth creasing the air’s upward motion. work together for each flight to airline ride. ■

16 150/1999