Dynamics of the Land–Sea Breeze System and the Surface Current Response in South-West Australia

Abstract

The land–sea breeze (LSB) system, driven by the thermal contrast between the land and the adjacent ocean is a widely known atmospheric phenomenon, which occurs in coastal regions globally. South-west Australia experiences a persistent and one of the strongest LSB systems globally with maximum wind speeds associated with the LSB system often exceeding 15 ms−1. In this paper, using field measurements and numerical simulations, we examine: (1) the local winds associated with the land–sea breeze with an emphasis on the ocean; and, (2) the response of the surface currents to the diurnal wind forcing. The measurements indicated that the wind speeds decreased between midnight and 0400 and increased rapidly after 1100, reaching maxima >10 ms−1 around 1800) associated with the sea breeze and decreased to midnight. Wind directions were such that they were blowing from south-east (120°) in the morning and changed to almost southerly (~200°) in the afternoon. Decomposition of the wind record to the diurnal and synoptic components indicated that the diurnal component of winds (i.e., LSB) was oriented along the south-west to north-east axis. However, the stronger synoptic winds were from the south-east to south quadrant and in combination with the LSB, the winds consisted of a strong southerly component. We examined the evolution, horizontal extent, and propagation properties of sea breeze fronts for characteristic LSB cycles and the sea breeze cell propagating offshore and inland. The results indicated that the sea breeze cell was initiated in the morning in a small area, close to 33° S, 115.5° E, with a width of ~25 km and expanded onshore, offshore and alongshore. The sea breeze cell expanded faster (30 kmh−1) and farther (120 km) in the offshore direction than in the onshore direction (10 kmh−1 and 30–40 km). Winds during the LSB cycle followed a counterclockwise rotation that was also reflected in the surface currents. The winds and surface currents rotated anticlockwise with the surface currents responding almost instantaneously to changes in wind forcing but were modified by topography. The diurnal surface currents were enhanced due to the resonance between the LSB forcing and the inertial response.

Seasonal Variation of the Land Breeze System in the Southwestern Bay of Bengal and Its Influence on Air‐Sea Interactions

“…The direction of the current vector anomaly is approximately 90° left to the wind direction (Figures 9a–9c). Previous studies on the LBS, particularly on the north of 30°N, where the inertial period is less than a day, showed that the current modulation with respect to diurnal wind forcing is as expected from classical Ekman drift theory (Fontán et al., 2013; Rafiq et al., 2020) in which the current is directed to the right of the winds. In our case, the inertial period is ∼2 days at the buoy location, which is much longer than the diurnal time scale of the LBS wind forcing.…”

“…However, a few studies have examined the impact of the LBS on different parts of the global ocean. Neetu et al (2006) studied the impact of the LBS on ocean surface waves over the eastern Arabian Sea and Rafiq et al (2020) studied the impact of the LBS on coastal currents of the southwestern Australian coast. Based on moored buoy observation in the Red Sea, Davis et al (2019) have shown that the LBS has the potential to modulate local air-sea interaction processes.…”

Finding lobsters: investigating a period of unusually low settlement of

“…Surface current variability on the continental shelf within the study region is predominantly wind-driven (Fig. 2a; Smith et al 1991;Pattiaratchi et al 1997;Rafiq et al 2020). Southerly wind stresses overcome the alongshore pressure gradient during the summer months, moving upper layers offshore and favouring upwelling onto the continental shelf (Pearce and Pattiaratchi 1999).…”

The Influence of Reef Topography on Storm-Driven Sand Flux

“…In this region, the diurnal tidal component has a maximum range of 0.60 m and the semidiurnal tide has a range of only 0.20 m [26]. There are three main wind regimes [27,28]: (1) calm winds (<5 ms −1 ); (2) strong winds associated with the passage frontal systems in winter with wind speeds >15 ms −1 with wind direction changing anti-clockwise from north to west to southwest; and (3) summer sea breezes (alike to a daily storm) with wind speeds >15 ms −1 blowing over 2-3 days from the south. Wind data from the Rottnest Island station over 2009-2016 indicated that the mean number of storms per year was 42 (range: 39-50) while 40% and 25% of the storms occurred during winter and summer months, respectively [27].…”