An Improved Understanding of Low-Level Thermodynamic Conditions Near the Tropical Cyclone Inner Core
Principal Investigator:
Joseph J. Cione
Collaborating
scientist(s):
Peter Black (HRD)
Objective:
Through observations, obtain an improved physical understanding of air-sea interaction processes and boundary layer thermodynamics within and outside the tropical cyclone (TC) inner core.
Rationale:
Up until very recently, observations of the TC boundary layer, especially within the inner core high wind region, have been extremely rare. The severe lack of data within the TC boundary layer has forced theoreticians and TC modelers alike to make severa
l assumptions regarding the thermodynamic structure of the TC boundary layer, including the critically important air-sea interface, where ocean-atmosphere exchanges of heat and moisture occur. Despite the lack of observations, it is currently conventiona
l wisdom that surface air temperature (SAT) and sea surface temperatures (SSTs) within the TC environment are nearly uniform in the horizontal and are close to neutrally buoyant (i.e. SST-SAT ~ 0-1K). The specific purpose of this study is to determine th
e validity of these critical assumptions while the more general charge of this observational research is to dramatically improve our physical understanding of the rarely observed TC atmospheric boundary layer, including observations within the TC inner co
re.
Method:
Use drifting buoy, moored buoy and Coastal Marine Automated Network (C-MAN) observations in cases where buoys/platforms came in close proximity to 1975-1997 Atlantic basin and Gulf of Mexico TCs in order to build composite analyses of surface moisture, ai
r and sea temperatures within the vicinity of the TC inner core. Also, when available, obtain data from the newly acquired Global Positioning Satellite (GPS) dropwindsondes in order to accurately determine near surface/boundary layer structure in and aro
und the TC inner core.
Accomplishment:
Near-surface wind and thermodynamic observations were obtained from fixed buoys, drifting buoys and Coastal Marine Automated Network (C-MAN) platforms for 26 TCs between 1975-1997. During this 22-year period, more than 160 'TC-buoy encounters' with over
8,000 individual observations were compiled. Preliminary findings from this study illustrate that previous assumptions of near-surface, thermodynamic horizontal homogeneity and atmospheric neutrality are often not supported near the TC inner core. From
this data set, substantial sea-air contrasts (i.e. SST -SAT) greater than 2.5K were repeatedly observed within the TC high wind regime. These observations suggest that the low-level TC inner core, under certain circumstances, may exhibit strong near-surf
ace instability and be typified by large surface fluxes of heat and moisture (Figure). It is believed that these individual surface observations, when looked at in a composite sense, will both offer new insight and significant
ly improve our physical understanding of the infrequently observed near-surface TC inner core. A journal article describing the major findings from this observational research is currently underway.
Key reference:
Cione, Joseph J. , 1997: 1975-1996 Tropical cyclone 'close encounters': An observational investigation of surface conditions within the high wind regime of Gulf of Mexico and Atlantic basin hurricanes. Preprint >from the AMS Conference on Air-Sea
Interaction Phoenix, Arizona, 11-16 January 1998.
Cione, Joseph J., and P. Black, 1997: Surface temperature observations within the tropical cyclone inner core. Preprint from the AMS Conference on Tropical Cyclone Intensity Change; Phoenix, Arizona, 11-16 January, 1998.
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