This study uses both observed and simulated data to investigate the diurnal evolution of land and sea-breeze (LSB) circulation across the Guinean Coast of West Africa. Numerical simulations, with ERA-Interim and CFS as forcing data, were carried out using a modified WRF-ARW model code to evaluate the model’s ability to capture the LSB kinematics over West Africa. Two simulation runs were performed with each data set. Comparison of the simulated and observed winds showed that the WRF model was able to capture the rotation of LSB in the coastal areas of the region very well. Results also showed that the simulated diurnal evolutions of the hodographs and onshore/offshore winds were found to be in good agreement with the observations. Furthermore, the simulations showed complex patterns of clockwise (CR) and anti-clockwise rotations (ACR) across the Guinean Coast. The sense of rotation is a result of complex interaction between surface and synoptic pressure gradients, horizontal and vertical diffusion, and advection terms. Overall, the results of the analysis showed that the balance is not always dominated by the pressure gradient terms, as suggested by earlier studies. However, hourly analysis of the rotation terms strongly indicates that over the ocean, surface pressure gradients dominate, while diffusion terms are more important over land areas. The Coriolis term was found not to be significant, the study area being close to the equator. Significantly, regions over water are found to be dominated by ACR, while land areas showed more CR. This may be attributed to the variation of surface roughness due to the landscape and urbanization.

Numerical simulation of land and sea-breeze (LSB) circulation along the Guinean Coast of West Africa

Focusing on the components of fine particulate matter, i.e., PM2.5, we have analyzed the factors that led to the high concentrations of each chemical component in PM2.5 during our observations in Fukuoka, Japan in spring 2020. The backward trajectory showed that air masses reached Fukuoka via the Yellow Sea and the southern part of South Korea when PM2.5 and each chemical component were high in concentrations. On the other hand, diurnal variations in ozone were also observed, suggesting that both transboundary and local air pollution are involved. Air masses reached the southern part of the Kyushu region when only sulfate concentrations were high. A volcano eruption led the high sulfate concentration. When only polycyclic aromatic hydrocarbons (PAHs) concentrations were high, air masses often reached the northern part of Kyushu, indicating that there may be a specific local source for PAHs.

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Analysis of Chemical Components of Fine Particulate Matter Observed at Fukuoka, Japan, in Spring 2020 and Their Transport Paths

This study uses observed and simulated data to analyze the dynamics LSB rotation along the Guinean Coast of West Africa. A non-hydrostatic fully compressible numerical model is used to simulate LSB circulation. To evaluate the model’s ability to capture the LSB kinematics, the study used a modified model code with ERA-Interim and CFS as forcing data. Comparison of observed and simulated LSB patterns shows that the model reliably captures the LSB circulation in the region. The simulated diurnal evolutions of hodographs and onshore/offshore winds also follow the observations. A dynamical analysis performed by extracting individual forcing terms from the horizontal momentum equations at selected regions within the study area showed that the direction of the wind rotation is a result of a complex interaction between surface and synoptic pressure gradients, advection, and horizontal and vertical diffusions forces. However, hourly analysis of the rotation term suggests that surface gradient seems to dominate over oceanic region, while diffusion terms are more important for land area. This may be attributed to the variation of surface roughness due the landscape and urbanization. Therefore, this reveals the link between urbanization and LSB circulation in coastal region of West Africa, where most important cities are located. 

/pdf/numerical-simulation-of-land-and-sea-breeze-lsb-circulation-1jol5jea.pdf

Numerical Simulation of Land and Sea Breeze (LSB) Circulation along the Guinean Coast of West Africa

Behaviors of sea breeze above Fukuoka City have been investigated on the basis of AMeDAS data and field observations. The land and sea breeze is influenced strongly by the topography near Fukuoka City and blows steady along the northwest-southeast line. Sea breeze observations performed by using a doppler sodar have revealed the existence of a coherent structure consisted of a pair of ascending and descending currents. The cross-correlation coefficients between horizontal andvertical velocities vary with 30 min period and take a value nearly equal to zero when the time lag is 0. Therefore, it is concluded that the coherent structuremay be due to the internal wave motion induced by the shear instability.

Behaviors of sea breeze above fukuoka city

Field observations to investigate the structure of sea breezes have been made on Fukuoka Plain. The intrusion speeds of sea-breeze front are estimated from the distributions of horizontal wind divergence. The wind velocity before and after the arrival of sea-breeze front has been measured by using a Doppler sodar, and the vertical profiles of mean wind speed, standard deviation of horizontal and vertical wind velocities and turbulent kinetic energy have been obtained. They are normalized by using the maximum wind speed and the height at a half of the maximum speed. Especially, the normalization for the wind speed profiles seems to give a good similarity.

Soichiro Sakai

Papers

Behaviors of sea breeze above fukuoka city

Vertical profiles of mean wind speed and turbulent characteristics of sea breezes