Study on Diurnal Sea Surface Warming and a Local Atmospheric Circulation over Mutsu Bay

Abstract

This study aims to investigate diurnal sea surface temperature (SST) rise in Mutsu Bay, and its relationship with the local atmospheric field. First, the characteristics of diurnal SST warming is revealed, using satellite and buoy data during 1995-2000. Satellite observations can clearly capture large diurnal SST rise that reaches a few degrees, and clarify the spatial distribution of the SST rise. The diurnal variation of the satellite-derived SST will reflect that of skin SST, which is defined as the temperature of the top layer with the thickness of a few tens micrometers. The analysis of the bulk SST observed with buoys at 1-m depth reveals that the frequency of large diurnal amplitude of SST (DSST) appearance becomes high from April to August, and the bulk DSST exceeds 1.0 K in some places in the bay for 71% of the days in July. Over the bay, surface air temperature in the daytime is higher than the bulk SST on average in April-August. From spring to summer the wind becomes weaker, and the easterly wind becomes frequent. The weak wind plays a role in promoting the diurnal SST rise, and the warm air-temperature may also secondarily contribute to large DSST.A model experiment is then performed to examine a local atmospheric circulation that develops around the bay under a clear and calm condition in summer, and to address the interaction between the circulation, and the diurnal SST warming. A local circulation forced by the land surface solar heating of this area produces the weak easterly surface wind and the subsidence of the air, and makes the air warmer over the bay. This is consistent with the observational results. In such a case, the diurnal rise of skin SST simulated by an ocean model exceeds 2 K all over the bay, and it is especially large in the northeastern area. If the diurnal skin SST rise is considered in the atmospheric model, although the circulation pattern does not change, the circulation becomes weaker and the surface air temperature inCorresponding author and present affiliation: Yoshimi Kawai, Independent Administrative Institution,

Sensible Heat Transfer on Atmospheric-Oceanic Boundary in the Outer Ambon Bay of Indonesia

“…SST warming over the eastern equatorial Pacific weakens Walker circulation which triggers an El Nino episode (Lau and Yang, 2003;Meyers et al, 2007). In coastal environment, SST significantly influences atmospheric condition over urban areas (Oda and Kanda, 2009;Pullen et al, 2007;Kawai and Wada, 2007;Kawai et al, 2006) that potentially affects the local weather (Yoshikado, 1992;Fujibe, 2003;Kobayashi et al, 2007). In turn, atmospheric variability, which can manifest through anomalous atmospheric convection, influences SST through cloud-radiation, wind-evaporation effect, wind induced oceanic mixing and upwelling (Kirtman and Vecchi, 2011).…”

A case study of sea breeze blocking regulated by sea surface temperature along the English south coast

“…More recent studies have concluded that the impact of SST on the sea breeze is stronger than was previously thought. Kawai et al (2006) investigated the effect on the surface wind field of a diurnal variation in SST within Mutsu Bay, Japan -a semi-enclosed sea. Diurnal SST variation is climatologically high in most semi-enclosed to fully enclosed seas such as the Mediterranean, the Arabian Sea, the Sea of Okhotsk and the Sargasso Sea.…”

“…Due to this, Kawai and Wada (2007) estimated that the simulated heat flux from the ocean is underestimated by an average of 10 Wm −2 by midday if SST is held constant. Kawai et al (2006) analyzed SSTs from NOAA AVHRR satellite retrievals and in situ buoy data and found that for over 80 % of the days between April and September when the diurnal SST signal exceeded 1.0 K the daytime upslope wind speed remained below 5.0 ms −1 . By comparing numerical simulations of the sea breeze with and without a coupled mixed-layer ocean model, Kawai et al (2006) demonstrated that, while the sea breeze circulation does not change structurally, the circulation was weaker in the coupled diurnally varying SST run than in the uncoupled fixed SST control run.…”

“…Kawai et al (2006) analyzed SSTs from NOAA AVHRR satellite retrievals and in situ buoy data and found that for over 80 % of the days between April and September when the diurnal SST signal exceeded 1.0 K the daytime upslope wind speed remained below 5.0 ms −1 . By comparing numerical simulations of the sea breeze with and without a coupled mixed-layer ocean model, Kawai et al (2006) demonstrated that, while the sea breeze circulation does not change structurally, the circulation was weaker in the coupled diurnally varying SST run than in the uncoupled fixed SST control run. Tang (2012) investigated the effect of hourly updated SST in a convection-permitting numerical model simulation of the sea breeze in the southern UK.…”

Low-Level Easterly Winds Blowing through the Tsugaru Strait, Japan. Part II: Numerical Simulation of the Event on 5–10 June 2003

“…2) We need to look into the diurnal cycles of the local wind accelerations. As possible causes, Part I has suggested diurnally varying cool-air intrusion into the strait and the bay from the east, and complex distribution of land and sea with differential heating and cooling on the basis of Kawai et al (2006). To address these challenges, analyses of numerical simulation data are indispensable.…”