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Hello Dolly! Tropical Cyclone Season has “un”officially arrived!

Posted On: July 28, 2008 - By: CIRA Web

Jeff Braun

As Hurricane Dolly made its way into southern Texas July 24, 2008 with 100+ mph winds, drenching a 40 mile wide and 100mile long stretch, along and north of the Rio Grande River, with anywhere between 8 and 22 inches of rain, it heralded the true beginning of tropical cyclone season here in the lower 48.  Yes, the “official” season starts on June 1st and we have already had named storms in both the Atlantic and Pacific, however, this was the first direct hit that the USA has taken in the new year.  Tropical Storm Arthur formed near coastal Belize and then immediately tracked westward into Mexico.  Hurricane Bertha started out as a wave off the coast of Africa, reaching hurricane strength (as high as a category 3 for a short time) northeast of the Windward Islands and then weakened back to tropical storm intensity a hundred miles or so south southeast of Bermuda.  Several days later, after passing almost directly over the island of Bermuda, it slowly headed off to the northeaast where it regained category 1 intensity briefly before heading into the much cooler waters of the North Atlantic.  Of note:  While Bertha did not bother too many interests other than Bermuda and the shipping industry, it did wander the waters of the Atlantic for well over two weeks.  Just before the appearance of Dolly, Torpical Storm Cristobal formed near the gulfstream waters just east of Savannah, Georgia.  Cristobal tracked to the northeast, along and away from the eastern coast of the USA,  for the next 5 days – becoming extratropical on July 23rd.  Cristobal provided areas of much needed rain to the southeastern USA in addition to some good breakers for the surfers up the coast.   In the Pacific, there have been 7 named storms from Alma to Genevieve, however, most of those have had little direct impact (again, other than the shipping business) on the USA.�


(Courtesy NASA/MODIS/TERRA – July 23, 2008 – at landfall)

The week of July 27th is turning out to be on the slow side  – northern hemisphere, tropical cyclone speaking – so I thought, during this lull, that I would mention what the primary missions of this year’s (2008) Hurricane Field Program are …in the case that you haven’t already heard about them (from the 2008 Hurrcane Field Program Plan, signed June 30, 2008):

(1) Three-Dimensional Doppler Winds: This is a multi-option, single-aircraft operational missiondesigned to use the NOAA P-3 to sample TCs ranging in intensity from tropical depression to a major

hurricane. The definition is meant to separate this category from tropical waves and disturbances that have yet to develop a well-defined warm-core circulation. The main goals of these missions is: 1) to improve understanding of the factors leading to TC intensity and structure changes, 2) to provide a comprehensive data set for the initialization (including data assimilation) and validation of numerical hurricane simulations (in particular HWRF), 3) to improve and evaluate technologies for observing TCs, and 4) to develop rapid real-time communication of these observations to NCEP. The overall experiment is comprised of two parts: one designed to obtain regular 12- or 24-h resolution airborne Doppler-radar observations of hurricanes, with optional dropwindsondes, and one, the National Environmental Satellite, Data, and Information Service (NESDIS) Ocean Winds and Rain Experiment, designed to improve understanding of microwave surface scatterometery in high-wind conditions over the ocean by collecting surface scatterometery data and Doppler data in the boundary layer of hurricanes.

(2) Tropical Cyclone Landfall and Inland Decay Experiment: This is a multi-option, single-aircraft experiment designed to study the changes in TC surface wind structure near and after landfall. It has several modules that could also be incorporated into operational surveillance or reconnaissance missions. An accurate description of the TC surface wind field is important for warning, preparedness, and recovery efforts. It addresses IFEX Goals 1, 2, and 3.

(3) Tropical Cyclone Unmanned Aerial System (UAS) Inflow/Eyewall/Eye Experiment: This is a multioption, multi-aircraft experiment that uses the Aerosonde UAS and dropwindsondes or aircraft expendable bathythermographs (AXBTs) launched from the NOAA P-3 to fully demonstrate and utilize the unique capabilities of the Aerosonde platform to document areas of the TC environment that would otherwise be either impossible or impractical to observe. It is planned that this effort will be based in Barbados. The immediate focus is to document and significantly improve understanding of the rarely observed TC boundary layer and undertake detailed comparisons between in-situ and remote-sensing observations obtained from manned aircraft (NOAA P-3 and Air Force Reserve (AFRES) C-130) and satellite-based platforms. In addition, a primary objective of this effort is to provide real-time, near-surface wind observations to NHC in direct support of NOAA operational requirements. These unique data will also be made available to EMC for both model initialization and forecast verification purposes. This addresses IFEX Goals 1, 2, and 3.

(4) Tropical Cyclogenesis Experiment: This multi-option, multi-aircraft experiment is designed to study how a tropical disturbance becomes a tropical depression with a closed surface circulation. It seeks to answer the question through multilevel aircraft penetrations using dropwindsondes, flight-level data, and radar observations on the synoptic, mesoscale, and convective spatial scales. It will focus particularly on dynamic and thermodynamic transformations in the low-and mid-troposphere and lateral interactions between the disturbance and its synoptic-scale environment. It addresses IFEX Goals 1 and 3. (5) Nadir Off-set SFMR Experiment: This is a single-aircraft experiment designed to obtain measurements off nadir of the sea surface to help develop retrieval models for the HIRAD.

(6) Tropical Cyclone/AEW Arc Cloud Experiment: This is a single-aircraft experiment, designed to collect observations across arc cloud features in the periphery of an AEW or TC using aircraft flight-level and dropwindsonde data to improve understanding of how these features may limit short-term intensification. Observations could be made using either the P-3 aircraft conducting another experiment, or the G-IV during a synoptic surveillance mission.

(7) Saharan Air Layer Experiment: This is a multi-option, multi-aircraft experiment which usesdropwindsondes launched from the NOAA G-IV and NOAA P-3 to examine the thermodynamic andkinematic structure of the SAL and its potential impact on TC genesis and intensity change. The dropwindsonde release points will be selected using real-time GOES SAL tracking imagery from UWCIMSS and mosaics of SSM/I total precipitable water from the Naval Research Laboratory. Specific effort will be made to gather atmospheric information within the SAL as well as regions of high moisture gradients across its boundaries and the region of its embedded mid-level easterly jet. The goals are to better understand and predict how the SAL dry air, mid-level easterly jet, and suspended mineral dust affect Atlantic TC intensity change and to assess how well these components of the SAL are being represented in forecast models. It addresses IFEX Goals 1 and 3. 8) Sea-Salt Aerosol and Cloud Base Number Concentration Experiment: This single-aircraftexperiment is a downwind flight leg outside the eyewall in relatively clear air, or just inside the inner edge of the eyewall. It will measure the concentrations of sea-salt aerosol and CCN concentrations below cloud base (1200- to 2000-ft flight levels are likely) in tropical storms and category 3 or less TCs, as well as approximately 200 ft above cloud base.

(9) Eyewall Microphysics Experiment: This is a single-aircraft, high-altitude penetration of eyewall convection, designed to document the ice-phase microphysics of the eyewall better than ever before, to benefit microphysical parameterizations in simulation of TCs. This could improve modeling of precipitation production, thus accurately estimating latent heat release (LHR) (affecting hurricane intensity) and rainfall quantitative prediction. It is preferred that it be flown at or above 20,000 ft. (10) TC-Ocean Interaction Experiment: This is a multi-option, single aircraft experiment acting insupport of upper ocean and air-sea flux measurements made by oceanic floats and drifters. One to three float and drifter arrays will be deployed into one or two mature storms by an AFRC C-130J and provide real-time ocean data. A NOAA P-3 will deploy dropwindsondes and make SFMR and Scanning Radar Altimeter (SRA) measurements within the float and drifter array as the storm passes over it. This work will be coordinated with NASA P-3 deployments of CTD probes.

(11) Hurricane Synoptic Surveillance: This is a multi-option, single or multi-aircraft operational mission that uses dropwindsondes launched from the NOAA G-IV, and the AFRES C-130 to improve landfall predictions of TCs by releasing dropwindsondes in the environment of the TC center. These data will be used by NCEP to prepare objective analyses and official forecasts through their assimilation into operational numerical prediction models. Because the atmosphere is known to be chaotic, very small perturbations to initial conditions in some locations can amplify with time. However, in other locations, perturbations may result in only small differences in subsequent forecasts. Therefore, targeting locations in which the initial conditions have errors that grow most rapidly may lead to the largest possible forecast improvements. Locating these regions that impact the particular forecast is necessary. When such regions are sampled at regularly spaced intervals the impact is most positive. The optimal targeting and sampling strategies is an ongoing area of research. This addresses IFEX Goal 1.

For more on the many (other) research oriented activities of the Hurricane Research Division (HRD) – part of the Atlantic Oceanographic and Meteorological Laboratory (AOML) – please follow this link: .

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