[1] In this paper we examine the variations of the boreal summer season sea breeze circulation along the Florida panhandle coast from relatively high resolution (10 km) regional climate model integrations. The 23 year climatology (1979-2001) of the multidecadal dynamically downscaled simulations forced by the National Centers for Environmental Prediction-Department of Energy (NCEP-DOE) Reanalysis II at the lateral boundaries verify quite well with the observed climatology. The variations at diurnal and interannual time scales are also well simulated with respect to the observations. We show from composite analyses made from these downscaled simulations that sea breezes in northwestern Florida are associated with changes in the size of the Atlantic Warm Pool (AWP) on interannual time scales. In large AWP years when the North Atlantic Subtropical High becomes weaker and moves further eastward relative to the small AWP years, a large part of the southeast U.S. including Florida comes under the influence of relatively strong anomalous low-level northerly flow and large-scale subsidence consistent with the theory of the Sverdrup balance. This tends to suppress the diurnal convection over the Florida panhandle coast in large AWP years. This study is also an illustration of the benefit of dynamic downscaling in understanding the low-frequency variations of the sea breeze.

1. Introduction

[2] Sea breeze is a regular feature of the summer season (June-July-August [JJA]) over Florida, especially over the Florida peninsula where there is usually a convergence of a double sea breeze front, one from the Atlantic coast and the other from the Gulf coast [Blanchard and Lopez, 1985]. Sea breeze fronts are typically forced by the temperature contrast between the warm land and the relatively cold ocean surface, creating a pressure gradient toward the land surface during daytime, which reverses at nighttime. Anthes [1978], using a 2-D mesoscale model, showed that the balance between the solenoidal term, the vertical diffusion of momentum, and the Coriolis force dominated the simulated sea breeze circulation.

[3] These sea breeze circulations and the consequent rainfall from it are typical mesoscale events, which are often not clearly captured in coarsely defined gridded observations. Here, we examine the variability of the sea breeze over Florida from a relatively high resolution (~10 km) regional climate model simulation.

[4] In an observational study, Blanchard and Lopez [1985] have characterized the south Florida sea breeze into 4 types based on their inland penetration and sea breeze intensity. They suggest that these sea breeze variations exist as a result of the background synoptic conditions. Similarly, Nicholls et al. [1991] from their modeling study conclude that sea breeze characteristics are related to the prevailing wind speed and direction. In this paper we propose that the large-scale variations of winds and temperature forced by the variability in the Atlantic warm pool [Wang and Enfield, 2001; Wang et al., 2006] have the potential to influence the sea breeze along the Florida coasts.

[5] For 1979-2001 we isolated 5 large and 5 small Atlantic Warm Pool (AWP) years, whose area of the AWP (enclosed by the 28.5° isotherm) in JJA was 1 standard deviation above and below the corresponding climatology, respectively. The average sea surface temperature (SST) [Smith et al., 2008] and 850 hPa winds from the National Centers for Environmental Prediction-Department of Energy (NCEP-DOE) Reanalysis II (also referred to as R2) [Kanamitsu et al., 2002] for the 5 large and 5 small AWP years are shown in Figures 1a and 1b, respectively. In years of large AWP, the trade winds are relatively weak [Wang and Enfield, 2003; Wang et al., 2006] (Figure 1c), the Caribbean Low Level Jet (CLLJ) is also weak [Wang et al., 2007; Chan et al., 2010], evaporation from the ocean surface is weak [Misra et al., 2009], and there is an increased cloud radiative feedback resulting in decreased longwave radiative loss [Wang and Enfield, 2001]. All of these lead to warmer temperatures of the ocean surface (Figure 1c). An estimate of the composite mean difference of the JJA seasonal mean rainfall from observations between these large and small AWP years (Figure 2), shows that the largest negative differences are found in the panhandle of Florida, followed by central and south Florida. In large AWP years, these regions of Florida have less summer seasonal rainfall than in small AWP years (Figure 2c). We contend in this paper that these differences of seasonal mean rainfall especially along the northwestern coast of Florida are related to corresponding changes in the sea breeze circulation forced by the AWP variations.

[6] In the next section we describe the regional climate model used in this study and provide details of the conducted model experiments. The results are presented in section 3 followed by a discussion in section 4. The concluding remarks are included in section 5.

Figure 1. (left) The JJA average SST (°C) from ERSSTV3 [Smith et al., 2008] and corresponding 850 hPa winds (m s-1) from NCEP-DOE reanalysis [Kanamitsu et al., 2002] for five (a) large (1981, 1987, 1995, 1998, 1999) and (b) small (1984, 1986, 1989, 1993, 1994) AWP years. [larger image]	Figure 2. (right) The JJA averaged CPC rain gauge based precipitation [Higgins et al., 2000] for the (a) five large AWP years (from Figure 1), (b) five small AWP years (from Figure 2), and (c) difference of Figures 2a-2b. The units are in mm d-1. [larger image]

S. Chan, J. J. O'Brien, and L. Stefanova, Center for Ocean-Atmospheric Prediction Studies, Florida State University, Tallahassee, FL 32306, USA.
V. Misra and L. Moeller, Department of Earth, Ocean and Atmospheric Science, Florida State University, Tallahassee, FL 32306, USA. (vmisra@fsu.edu)
N. Plant, St. Petersburg Coastal and Marine Science Center, U. S. Geological Survey, 600 Fourth St. S., St. Petersburg, FL 33701, USA.
T. J. Smith III, Southeast Ecological Science Center, U. S. Geological Survey, 600 Fourth St. S., St. Petersburg, FL 33701, USA.

SOFIA Project: Dynamics of Land Margin Ecosystems: Historical Change, Hydrology, Vegetation, Sediment, and Climate