Relative Humidity over the West Florida Continental Shelf

Abstract

Observed relative humidity variations on the coastal ocean of the West Florida Continental Shelf (WFS) are examined over the 5-yr period 1998-2003. Despite considerable daily variability within seasons, the monthly mean values are nearly constant at about 75%. Summertime specific humidity is twice that during winter, so high air temperatures are responsible for the low summer monthly mean relative humidities. Winter has the greatest relative humidity variability; values range from less than 50% to over 100% as extratropical fronts move over the WFS. Saturation (and fog) occurs as warm moist air passes over colder water. Two different sensors, mounted on multiple moorings, were used to make these observations. Monthly mean values from the Rotronics MP-100F are higher than the Hygrometrix 1020SHT. In addition to sensor differences, a contributing cause to this offset appears to be the locations chosen for sensor deployment. NCEP reanalysis climatology over the WFS and land-based coastal data both show an annual cycle in monthly mean relative humidity, with higher values in summer, suggesting that the reanalysis field is influenced by land. Air-sea fluxes over the WFS are sensitive to small spatial variability in the coastal ocean and atmosphere. The large grid spacing of the NCEP reanalysis does not capture this variability. The lack of coastal ocean data for assimilation biases the NCEP reanalysis fields toward land-based measurements. Increased spatial coverage via evolving Coastal Ocean Observing Systems should remedy this problem by providing required information for describing and understanding the complicated ocean-atmosphere interactions that occur on continental shelves.

Seasonal and spatial variation in the stable isotopic composition (δ18O and δD) of precipitation in south Florida

“…Annual relative humidity (R.H.) over the waters of the west Florida Shelf average near 75% (Virmani and Weisberg, 2005), with lower R.H. values in the summertime due to higher air temperatures. This average annual R.H is also similar to that measured at Miami airport of 74% (www.ncdc.noaa.gov), therefore, higher R.H. values do not seem to be responsible for the lower d-excess and lower isotopic values measured at Long Key.…”

An ammonium enrichment event in the surface ocean: Wind forcing and potential ramifications

“…Then both wind speed and barometric pressure increased rather sharply, mostly during JD 116. These wind-speed and barometric-pressure patterns indicate the approach and passage of a low-pressure weather front (Virmani and Weisberg, 2005). The period of calming winds ahead of the front was of particular interest because it matched so well with the period in which the strong surface and subsurface [NH 4 + ] maxima were present-i.e., the ammonium event in JD 112-116 (Section 3.2).…”

“…For example, each year that region receives on average 7-8 winter weather fronts (Virmani and Weisberg, 2005) such as observed in FSLE V and VI, and 24-hour, low-pass filtered hourly wind-speed data from the nearby COMPS current mooring C10 (Fig. 1) established that wind speeds persisted below 4 ms −1 for two days or more 72 times in 2001, suggesting ample opportunities during a year for calming winds to permit ammonium accumulation.…”

Linkages between environmental conditions and recreational king mackerel (Scomberomorus cavalla) catch off west‐central Florida

“…Fishing locations recorded outside the study area and within Tampa Bay or Charlotte Harbor were not included in the study. The general circulation of this area as a result of wind, thermal stratification, topography, and fresh water inputs has been described previously (Schmidt et al, 2001;Hu et al, 2004;Virmani and Weisberg, 2005;Weisberg et al, 2005). These oceanographic processes generate cross-shelf gradients in physical, biological, and chemical properties, and cross-and along-shelf transport of nutrients and plankton (Del Castillo et al, 2001;Gilbes et al, 2002;Paramo and Viana, 2002;Hu et al, 2004;Weisberg et al, 2005).…”