**1. Introduction**

The theory of land and sea breezes (LSB) is based on the thermal contrasts between the land and water. During the day, the land is warmer than the sea because of heating from the sun. Hence, the warm air over the land rises and expands forming cumulus clouds, while cooler air from the sea surface therefore flows inland to replace the rising warm air. The resulting circulation can move several kilometers inland as onshore wind circulation, called sea breeze. At night, the land cools faster than the

nearby ocean and a shallow mesoscale pressure gradient develops, with a higher surface pressure over the land. The resulting circulation is directed from the land to the sea (offshore circulation) near the surface, called land breeze.

Generally, the land breeze (LB) circulation is weaker than the sea breeze (SB) in both velocity and height of development because the heat source for the land breeze is much weaker than the heat source for the sea breeze circulation [1]. LB fronts tend to only affect a small area of the sea, in comparison with the much larger effect of SB.

In West Africa along the Guinea coast, LSB circulation occurs almost throughout the year although in varying strength [2, 3]. During the day, the circulation is driven by strong heating, while at night it is driven by cooling of the landmasses and resulting pressure anomalies. In tropical West African region, Coulibaly et al. [4] showed the winter frequency and the seasonality behaviors of LSB with both clockwise (anticyclonic) and anticlockwise (cyclonic) hodograph rotations. Kusuda and Alpert [5] and Haurwitz [6] evaluate the diurnal evolution of SB in the Northern Hemisphere with an influence of the Coriolis force in the sense of rotation, while over Sardinia (mid-latitude), the sense of rotation seems to be influenced by the combination of surface and synoptic pressure gradients and Coriolis and advection forces [7].

LSB is more frequently and prominently observed in tropical regions than in higher latitudes due to strong radiative heating, convection, and weak Coriolis force. It is also influenced by the prevailing large-scale wind and topographic friction. When LSB circulation prevails on land, changes in the temperature structure, humidity, and roughness occur in the air adjacent to the coast and lead to formation of a thermal internal boundary layer (TIBL) [8]. This effectively reduces the mixing height in the coastal regions in the daytime. LSB circulation and TIBL are the two important phenomena that influence the pollution plume direction and diffusion in coastal regions. Many factors such as topography, synoptic flow, and latitude are shown to influence the evolution and characteristics of the SB.

With the growing computational power and resulting improved modeling capabilities, numerical simulations of LSB circulation have gained attention since the 1960s. Much of the earlier numerical work was performed using two-dimensional hydrostatic models with coarse grid spacing (≈10 km). While these contributed greatly to our understanding of the mechanics and structure of the LSB circulation, they nevertheless remained highly idealized. Due to the large size of the model horizontal grid (>1 km), it is difficult to differentiate between hydrostatic and non-hydrostatic simulations [9]. While non-hydrostatic effects may weaken the mature nature of LSB, hydrostatic influence tends to overestimate LSB intensity [10]. Therefore, to adequately simulate LSB circulation and its associated features such as planetary boundary-layer (PBL) influence, it is decided to use three-dimensional models, even though two-dimensional models may be adequate for many idealized simulations [7].

Many theoretical and numerical modeling studies have been reported on the overall dynamics of the LSB circulations [7, 11–16]. Also, there have been observational and modeling studies of LSB characteristics over different regions [4, 7, 15–22].

However, the availability of non-hydrostatic numerical models with less than 1 km resolution has highlighted the complex nature of LSB and its associated nonlinear interactions on several scales [23]. Using numerical methods, Estoque [24] showed the development of a zone of low-level convergence at the leading edge of LSB current as it sets in over land, while Pielke [25] showed the effects of topographical friction on LSB evolution using a 3D numerical model. Therefore, numerical simulations can be considered as computational tools in minimizing the identified knowledge gaps by [7, 15] and assessing the governing factors in LSB dynamics over complex terrain and

*Numerical Simulation of Land and Sea Breeze (LSB) Circulation along the Guinean Coast… DOI: http://dx.doi.org/10.5772/intechopen.107339*

coastlines. Consequently, this study aims to evaluate the dynamics of LSB circulation over the Guinean Coast of West Africa using a fully compressible non-hydrostatic numerical model for simulating.

Based on the study by Moisseeva and Steyn [7] who used WRF-ARW version 3.4, this study will use WRF-ARW version 3.7.1 to examine the dynamics of LSB circulation over the region. The physics and dynamics of WRF-ARW version 3.7.1 allow the extraction of its dynamical factors related to atmospheric radiation, microphysics, planetary boundary layer and surface layer physics, land surface physics, and cumulus options of the model [16].

In winter period, Coulibaly et al. [4] showed both clockwise and anticlockwise rotations of the wind in coastal West Africa identifying some LSB episodes. This has been a good starting point for which the numerical modeling of the LSB circulation and hodograph rotation in the region has been based (see **Figure 1**).

#### **Figure 1.**

*Daily hodograph rotations of SB; a: January 1, 2011, b: May 12, 2011, c: August 30, 2011, d: December 13, 2011, e: December 16, 2014, and f: December 17, 2014. The numbers near dots indicate the hour of the day (LST).*
