Air-sea interaction at contrasting sites in the eastern tropical Pacific : mesoscale variability and atmospheric convection at 10°N
Farrar, J. Thomas
MetadataShow full item record
Tropical Pacific Ocean
KeywordOcean-atmosphere interaction; Cloud physics; Roger Revelle (Ship) Cruise Genesis 4; Thomas G. Thompson (Ship) Cruise TN73; Melville (Ship) Cruise PACS03MV
The role of ocean dynamics in driving air-sea interaction is examined at two contrasting sites on 125°W in the eastern tropical Pacific Ocean using data from the Pan American Climate Study (PACS) field program. Analysis based on the PACS data set and satellite observations of sea surface temperature (SST) reveals marked differences in the role of ocean dynamics in modulating SST. At a near-equatorial site (3°S), the 1997-1998 El Nino event dominated the evolution of SST and surface heat fluxes, and it is found that wind-driven southward Ekman transport was important in the local transition from El Nino to La Nina conditions. At a 10°N site near the summertime position of the Inter-tropical Convergence Zone, oceanic mesoscale motions played an important role in modulating SST at intraseasonal (50- to 100-day) timescales, and the buoy observations suggest that there are variations in surface solar radiation coupled to these mesoscale SST variations. This suggests that the mesoscale oceanic variability may influence the occurrence of clouds. The intraseasonal variability in currents, sea surface height, and SST at the northern site is examined within the broader spatial and temporal context afforded by satellite data. The oscillations have zonal wavelengths of 550-1650 km and propagate westward in a manner consistent with the dispersion relation for first baroclinic mode, free Rossby waves in the presence of a mean westward flow. The hypothesis that the intraseasonal variability and its annual cycle are associated with baroclinic instability of the North Equatorial Current is supported by a spatio-temporal correlation between the amplitude of intraseasonal variability and the occurrence of westward zonal flows meeting an approximate necessary condition for baroclinic instability. Focusing on 10°N in the eastern tropical Pacific, the hypothesis that mesoscale oceanic SST variability can systematically influence cloud properties is investigated using several satellite data products. A statistically significant relationship between SST and columnar cloud liquid water (CLW), cloud reflectivity, and surface solar radiation is identified within the wavenumber-frequency band corresponding to oceanic Rossby waves. Analysis of seven years of CLW data and 20 years surface solar radiation data indicates that 10-20% of the variance of these cloud-related properties at intraseasonal periods and wavelengths on the order of 10° longitude can be ascribed to SST signals driven by oceanic Rossby waves.
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2007
Suggested CitationThesis: Farrar, J. Thomas, "Air-sea interaction at contrasting sites in the eastern tropical Pacific : mesoscale variability and atmospheric convection at 10°N", 2007-02, DOI:10.1575/1912/1567, https://hdl.handle.net/1912/1567
Showing items related by title, author, creator and subject.
FASINEX Frontal Air-Sea Interaction Experiment (January-June 1986) : summaries for FASINEX mooring cruises; phase one: R/V KNORR Cruise 119, phase three: RV/KNORR Cruise 123 Pennington, Nancy J.; Weller, Robert A. (Woods Hole Oceanographic Institution, 1986-10)The Frontal Air-Sea Interaction Experiment (FASINEX) was a study of the response of the upper ocean to atmospheric forcing in the vicinity of an oceanic front in the subtropical convergence zone southwest of Bermuda, the ...
FASINEX Frontal Air-Sea Interaction Experiment (January-June 1986) : cruise summaries for FASINEX phase two; R/V OCEANUS cruise 175, R/V ENDEAVOR cruise 141 Pennington, Nancy J.; Weller, Robert A. (Woods Hole Oceanographic Institution, 1986-10)The Frontal Air-Sea Interaction Experiment (FASINEX) was a study of the response of the upper ocean to atmospheric forcing in the vicinity of an oceanic front in the subtropical convergence zone southwest of Bermuda, ...
Pennington, Nancy J.; Briscoe, Melbourne G. (Woods Hole Oceanographic Institution, 1979-12)102 profiles of conductivity, temperature, and depth (pressure) (CTD) were taken in the JASIN area northwest of Scotland in July-September 1978. These stations consisted of single and yo-yo profiles. The data set includes ...