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Through daily convection-permitting ensemble simulations conducted over a 3-month period, the forecast uncertainty for the land breeze and associated coastal rainfall during early-summer rainy season over South China is investigated. The ensemble includes 12 sets of physics parameterization schemes for boundary layer, radiation, surface layer, and land surface processes. Observations from air–sea buoys at sea, coastal weather stations, and radiosondes are employed to evaluate the diurnal variations and vertical structures of the simulated land breezes. Results suggest that the forecast uncertainty of land breeze circulations is closely associated with the model's representation of the nocturnal near-surface air temperature on land sides. A systematic underestimation of nocturnal air temperature is recognized in most ensemble members, while the diverse errors of daytime air temperature on land can be diminished through the ensemble mean. The cold bias tends to create stronger land breezes, resulting in prolonged and widespread coastal rainfall through more intensive coastal convergence. By comparing the relative contributions of multiple parameterization schemes, it is found that the systematic underestimation for nocturnal air temperature primarily results from the surface layer and land surface parameterization schemes. To improve the nighttime temperature forecast over this rainfall hotspot, it is essential to implement an advanced land surface model that incorporates complex thermodynamic processes tailored to this climate regime. Additionally, improved parameterization schemes for the planetary boundary layer and surface layer are necessary to enhance the nocturnal turbulent intensity under near-neutral conditions. [ABSTRACT FROM AUTHOR]

The planetary-boundary-layer (PBL) flow and above is investigated for the central north coast of Brazil, an equatorial region spanning from 8° to 2°S. The daily PBL flow is controlled by vertical entrainment of horizontal momentum from a southerly large-scale flow associated with the Hadley cell, and by a mesoscale pressure gradient force (PGF) created by the differential heating between land and ocean. Near the coast, the flow is from the north-east quadrant comprising a small rotation, probably caused by a weak mesoscale PGF and a weak Coriolis force. Inland it is north-easterly in the morning, but deep mixing during the afternoon brings down momentum from above causing it to become south-easterly. The mesoscale PGF executes a daily 360° rotation at most of the stations. In the afternoon it points to land due to continuous heating of the land, and a sea breeze develops in the presence of the background flow. Once convection dies out, the transfer of horizontal momentum is reduced, and the marine-air layer can flow faster into the continent as a nocturnal jet. As the stable boundary layer grows thicker, this flow tends to be eliminated at the surface. By morning, the mesoscale PGF points north, forcing the inland flow to become south-easterly, while on the coast flow becomes almost easterly. This scenario repeats during dry and wet seasons and can be understood as a consequence of the south–north propagation of an atmospheric circulation resembling a helix with its rotation axis oriented parallel to the shoreline. [ABSTRACT FROM AUTHOR]

The present work can be considered the first to examine the sea–land breeze phenomenon along the southern border of the Levantine Basin. Hourly records of wind regime (speed and direction) from five coastal meteorological stations distributed over this coastline were analyzed to characterize sea and land breezes in this region. The meteorological data also comprised simultaneous hourly air temperature and relative humidity records. The data covered 13 years from January 2007 to December 2019, with 0% missed data. The diurnal inversion of wind direction was utilized to recognize sea and land breeze days. This was verified by the reversal daily behavior of temperature and relative humidity. Statistics describing the onset, cessation, and seasonality of sea breeze occurrence are presented. Seasonally, sea breezes are most frequent in summer and early autumn months (July–October). Land breeze appears at most stations during night, with direction varying from one location to another among the five examined coastal stations. [ABSTRACT FROM AUTHOR]

This study analyses the atmospheric boundary layer over the Bilbao metropolitan area during summer (13-18 Jul 2009) and winter (20-29 Jan 2010) episodes using the Environment-High Resolution Limited Area Model (Enviro-HIRLAM) coupled with the building effect parameterisation (BEP). The main objectives of this study are: to evaluate the performance of the model to simulate the land-sea breezes over this complex terrain; to assess the simulations with the integration of an urban parameterisation in Enviro-HIRLAM and finally; and to analyse the urban-atmosphere interactions. Even if the hydrostraticity of the model is a limitation to simulate atmospheric flows over complex terrain, sensibility tests demonstrate that 2.4 km is the optimal horizontal resolution over Bilbao that allows at the same time: to obtain satisfactory reproducibility of the large-scale processes and to explore the urban effects at local scale. During the summer episode, a typical regime of diurnal sea breeze from the NW-N-NE direction and nocturnal valley breezes from the SE direction are observed over Bilbao. The urban heat island (UHI) phenomenon is developed in the city centre expanding to the suburbs from 22 to 10 local time (LT), covering an area of 130 km. The maximum UHI intensity, 1 °C, is reached at the end of the night (5 LT), and it is advected 12 km towards the sea by the land breezes. The urban boundary layer (UBL) height amplitude varies from 100 (night time) to 1,360 m (at 14 LT). During the winter episode, the land breeze dominates the atmospheric diffusion during the day and night time. The maximum UHI intensity, 1.7 °C, is observed at 01 LT. It is spread and remained over the city covering an area of 160 km, with a vertical extension of 33 m. The UBL reaches 780 m height at 16 LT the following day. [ABSTRACT FROM AUTHOR]

A case of offshore convective initiation by interacting land breezes near Darwin, Australia is investigated using convection-permitting model simulations, radar-derived precipitation observations, thermodynamic profiles from radiosonde soundings and surface measurements. These analyses elucidate the convergence of two land breezes in the Van Diemen Gulf, one originating from the Tiwi Islands and the other from mainland Australia; the convergence is sufficient to initiate a line of convection that forms parallel to the mainland coast in the early morning. While differing in small-scale features, the modeled system shows reasonably good agreement with the observed precipitation accumulations. However, using simulations with different initialization times and examining a second case, it is shown that the representation of the land-breeze system and subsequent convective initiation is very sensitive to the upstream wind and thermodynamic conditions, making correct simulation of these processes challenging. [ABSTRACT FROM AUTHOR]

In this study, the land-sea breeze circulation model coupled with a random-walk model is developed by the analysis of the formation and the mechanism of the land-sea breeze. Based on the data of the land-sea circulation in Dalian, China, the model simulated the diurnal variation of pressure, flow, temperature, and turbulent kinetic energy field and also provides a basis for solving the air pollutant concentration in the land-sea breeze circulation so as to estimate the economic cost attributable to the atmospheric pollution. The air pollutant concentration in the background of land-sea circulation is also simulated by a Gaussian dispersion model, and the results revealed that the land-sea circulation model coupled with the random-walk model gives a reasonable description of air pollutant dispersion in coastal areas. [ABSTRACT FROM AUTHOR]

The levels and temporal variations of surface ozone at a coastal site in East China during summer and autumn were analyzed and the influences of meteorological parameters on ozone were investigated. An inland city was chosen as a comparison site. The main results and conclusions of this study are: (1) ozone pollution, with a maximum 1 h concentration of 150.98 ppbv, was severe during summer and autumn at the coastal site; (2) the ozone level was obviously higher at the coastal site than that at the inland site in September; (3) besides temperature and solar radiation, sea-land breeze circulation is an important factor influencing the ozone level at the coastal site, and sea breeze often induce high ozone levels (the average ozone concentration for sea breeze was about 13 ppbv higher than that for land breeze). [ABSTRACT FROM AUTHOR]

The atmospheric haze over the Pearl River Delta (PRD) was investigated by using the Models-3 Community Multi-scale Air Quality modeling system with meteorological fields simulated by the Fifth-generation National Center for Atmospheric Research/Penn State University Mesoscale Model (MM5) from September 26th to September 30th, 2004. The model-simulated meteorological elements and particulate matter with aerodynamic diameter less than 10 μm (PM10) were compared with observations at four air quality-monitoring stations. The results showed that MM5 successfully reproduced the diurnal variations of temperature, wind speed, and wind directions at these stations. The temporal variations of the simulated values were consistent with those of the observed (such as temperature, wind speed, and wind direction). The correlation coefficient was 0.91 for temperature and 0.56 for wind speed. The modeling results show that the spatial distributions of simulated PM10 were closely related to the source emissions indicating three maxima of PM10 over the PRD. The sea–land breezes diurnal cycle played a significant role in the redistribution and transport of PM10. Nighttime land breeze could transport PM10 to the coast and the sea, while daytime sea breeze (SB) could carry the accumulated PM10 offshore back to the inland cities. PM10 could also be transported vertically to a height of up to about 1000 m because of strong turbulence in the SB front. Process analyses indicated that the emission sources and the vertical diffusion were the major processes to influence the concentrations of particulate matter with aerodynamic diameter less than 2.5 μm (PM2.5). [ABSTRACT FROM AUTHOR]

Low-pressure system (LPS), a major rain-bearing synoptic circulation, forming over the Indian region, including Bay of Bengal and Arabian Sea plays a vital role in performance of southwest monsoon over the country. The term LPS includes lows, depressions and cyclonic storms. According to the intensities, LPS are categorized into two, one only low-pressure areas (LPA) and the other more intense systems like depressions/storms (DDS). Statistical analysis reveals some significant results. Decadal analysis shows that there is a significant increase(decrease) in the frequency and duration of LPA(DDS) during the monsoon season for the recent decades. SST of Bay of Bengal also increased significantly during recent period. It is also observed that frequency and duration of LPA(DDS) show significant positive(negative) trend and sea surface temperature (SST) of the Bay of Bengal shows significant positive trend for the period after 1960. The total frequency of LPS has neither increased nor decreased significantly but the duration of LPS has significantly increased. This means, while the average total formation of the systems remains the same, the duration has increased. It seems that there are some atmospheric and oceanic conditions which are responsible for not allowing the intensification of lows into depressions. The frequency and duration of LPA(DDS) during the monsoon season are positively(negatively) correlated with SSTs of the Bay of Bengal during winter, pre-monsoon and monsoon season indicating warmer SST of the Bay of Bengal may not be favourable for intensifying lows into depressions. [ABSTRACT FROM AUTHOR]

This research provides a process for assessment of wind potential using descriptive statistics and spectral analysis. Advantages of spectral analysis are that it not only can identify significant periodic components but also can analyze phase lag and time lag of the significant components for the naturally occurring wind speed time series observed from different locations. On a regional scale, descriptive statistics and spectral analysis can be effectively used to screen out unqualified areas and determine the wind potential of a studied site. In order to demonstrate the method can be effectively used to assess wind potential by wind speed time series, six weather stations in Taiwan are used in this study. The results show that more than half of the observations for Wu-chi station had a mean wind speed of over 4 m/s. The prevailing main wind directions are suggested as being from the North and Northeast for all of the stations. Periodic semi-diurnal and diurnal components are significant for the studied wind speed time series. The results also show that the time lags for the weather stations are one hour or less using Pen-ghu station as a reference. [ABSTRACT FROM AUTHOR]

The planetary boundary-layer (PBL) parameterization is a key issue for the definition of initial wind flow fields in diagnostic models. However, PBL theories usually treat separately stable, neutral, and convective stability conditions, so that their implementation in diagnostic wind models is not straightforward. In the present paper, an attempt is made to adopt a comprehensive PBL parameterisation, covering stable/neutral and unstable atmospheric conditions, which appears suitable to diagnostic models. This parameterisation is implemented into our diagnostic mass-consistent code. A validation of the consistency between the implemented PBL parameterisations has been checked through an analysis of the sensitivity of the vertical wind profiles to atmospheric stability. [ABSTRACT FROM AUTHOR]

Climatological characteristics along the northern Croatian Adriatic coast have been examined for nine meteorological stations for the summertime sea/land breeze circulation. The stations considered are Pula-airport, Opatija, Rijeka, Senj, Malinska, Rijeka-airport, Mali Lošinj, Rab and Zadar. The hourly surface measurements at each station from June to September for the period 1991–2004 as well as the radiosoundings in Zadar (from 2002 to 2004) were used for the analysis. A dataset with the sea/land breeze days was formed according to the several criteria. The mean daily maxima of both air and sea surface temperatures were more influenced by the large scale disturbances toward north (e.g. in Rijeka or Opatija) compared to the values for e.g. Zadar. Furthermore, the influence of the large scale disturbances diminished toward the south concerning the sea–land temperature difference only at the stations placed at Rijeka Bay and Velebit channel. The strongest sea breeze was found at Pula-airport and the most frequent ones at Opatija and Zadar. At Senj the rarest, the weakest and the shortest sea breeze was observed. The climatological records of wind speed and air-sea temperature difference (Δ T) showed for Opatija, Malinska and Zadar that the maximum measured wind speed is around 4.5 °C confirming the nonlinear relationship between the sea breeze speeds and the Δ T during the day. At most stations, the clockwise rotation of the hodographs prevails which is typical for the Northern hemisphere due to Coriolis force, with the exception at Senj and Malinska. While the hodographs for Pula, Rijeka-airport and Mali Lošinj display a later onset of the prevailing sea breeze because of the interaction among several sea breeze circulations, the results for Opatija, Zadar and Senj show considerably distorted hodographs because of the nearby channeling of the air flow. [ABSTRACT FROM AUTHOR]

We, in the monsoonal regions of the world are concerned about the variation of rainfall in space and time and a major aim of monsoon meteorology is to predict these variations. Understanding the basic system responsible for the monsoon and the factors that lead to its variation is a prerequisite for developing models to generate these predictions. In this article, I discuss the basic system responsible for the monsoon - the wind and the rains. [ABSTRACT FROM AUTHOR]

Land breeze is a type of mesoscale circulation developed due to thermal forcing over a heterogeneous landscape. It can contribute to atmospheric dynamic and hydrologic processes through affecting heat and water fluxes on the land-atmosphere interface and generating shallow convective precipitation. If the scale of the landscape heterogeneity is smaller than a certain size, however, the resulting land breeze becomes weak and becomes mixed up with other thermal convections like thermals. This study seeks to identify a scale threshold to distinguish the effects between land breeze and thermals. Two-dimensional simulations were performed with the Regional Atmospheric Modeling System (RAMS) to simulate thermals and land breeze. Their horizontal scale features were analyzed using the wavelet transform. The thermals developed over a homogeneous landscape under dry or wet conditions have an initial scale of 2–5 km during their early stage of development. The scale jumps to 10–15 km when condensation occurs. The solution of an analytical model indicates that the reduced degree of atmospheric instability due to the release of condensation potential heat could be one of the contributing factors for the increase in scale. The land breeze, on the other hand, has a major scale identical to the size of the landscape heterogeneity throughout various stages of development. The results suggest that the effects of land breeze can be clearly distinguished from those of thermals only if the size of the landscape heterogeneity is larger than the scale threshold of about 5 km for dry atmospheric processes or about 15 km for moist ones. [ABSTRACT FROM AUTHOR]

The changes in the response of near surface aerosol properties to land- and sea-breeze circulations, associated with the changes in the prevailing synoptic meteorological conditions, are examined for a tropical coastal station. Aerosol properties are nearly similar in both the breeze regimes (land and sea) during seasons of marine airmass while they are distinct during seasons of continental airmass. As the prevailing winds shift from continental to marine and the ambient weather changes from winter conditions to the humid monsoon season, the submicron mode, which dominated the aerosol mass-size distribution, is largely suppressed and the dominance of the super micron mode increases. During periods of continental air mass (winter), the aerosol loading is significantly higher in the land-breeze regime, (particularly in the submicron range) but as the winds shift to marine, the loading initially becomes insensitive to the breeze regimes and later becomes higher in the sea-breeze regime, particularly in the super micron range. [ABSTRACT FROM AUTHOR]

A two-dimensional numerical model with a simplified land-use paramaterization is used to investigate the effects of land use topography on local circulation systems. A criterion is presented indicating the relative importance of land use on local circulations. Land-use contrast in the numerical model is parameterized by moisture availability and roughness length. Numerical experiments were carried out under various atmospheric stabilities with various dimensions for the mountains. Numerical results show the following: (1) Anabatic winds prevail in high mountains, while the land–land breeze is stronger when the horizontal contrast of the heat flux from each land surface is large. (2) In the early morning, anabatic winds tend to prevail over land–land breezes, but the land–land breeze tends to prevail in the later afternoon. (3) While atmospheric stability has a large influence on the mesoscale circulation, the horizontal scale of the mountain is not as important for the intensity of the mesoscale circulation. (4) In strong stable conditions or weak insolation, the anabatic wind tends to be more active than the land–land breeze; namely, the heat flux from inhomogeneous land use becomes a less important factor for the generation of a mesoscale disturbance than the orographic forcing in the case of strong atmospheric stability. (5) The predominant mesoscale circulation is predicted by a criterion based upon the horizontal adjustment theory of the mixed layer. The criterion proposed in this study is based on the mountain height, the ratio of the heat flux from the different land use patterns, the atmospheric static stability, and the time-integrated heat flux. The criterion gives results that generally agree with the numerical results. [ABSTRACT FROM AUTHOR]

Local circulation plays an important role in producing high-resolution meteorological and air quality information. In this study, detailed surface meteorological and vertical profile features about sea and land breezes in the Seoul Metropolitan Area (SMA) were investigated using the data from urban meteorological observation system in SMA (UMS-Seoul). These data were obtained from high-resolution surface meteorological stations and three wind lidar stations for 6 consecutive days (17-22 May 2016) with very weak synoptic winds and low cloud covers. The 6-day average diurnal variations of surface meteorological variables revealed temperature differences between land and sea, driving the pressure differences between the two. This induced sea-land-breeze circulation. The resulting sea breeze began at the shoreline at 1200 local standard time (LST), moved landward at a rate of about 10 km h−1, and reached 60 km from the shoreline at 1800 LST. The land breeze occurred within 50 km of the shoreline until noon. The sea-breeze front was identified by a steep horizontal temperature gradient, and its passage was accompanied by an abrupt temperature drop as well as vapor pressure and wind increases. The time-height cross section of wind indicated that the top of sea (land) breeze reached a maximum height of 1.5 km (0.8 km) with maximum winds 0.4 km (0.3-0.4 km) high in the late afternoon (early morning). The returning (easterly) flow at 1.5-1.6 km was clearly observed over the sea-breeze cells. [ABSTRACT FROM AUTHOR]

We analyze the hourly rainfall data of 30 rain gauges in Cambodia from 2010 to 2015 to focus on the diurnal pattern of rainfall and its regional characteristics, with the underlying mechanisms inferred from the observed data. The observed annual rainfall in inland Cambodia ranges from 1087 to 1528 mm on station-average. Approximately 5-20% of the annual rainfall occurs during the pre-monsoon season, 50-78% during the summer monsoon season, and 12-36% during the post-monsoon season. During the pre-monsoon season, rainfall is dominant on the coast and over the Cardamom Mountains, with a maximum in the afternoon. The rainfall amount is smaller around the Tonle Sap Lake. During the summer monsoon season, rainfall is larger in the northern region and smaller in the western region in inland Cambodia, in both amount and proportion to annual rainfall. The rainfall amount on the coast is distinctively large. The diurnal rainfall maximum occurs in the early afternoon in the Cardamom Mountains, in the afternoon on the plain at the southwestern side of the Tonle Sap Lake, in the evening on the wide area of the northeastern side of the lake, and in the early morning on the coast. The clear regional characteristics in the diurnal rainfall pattern suggest significant effects of local features, even during the Asian summer monsoon season. During the post-monsoon season, rainfall is larger on the southwestern side of the Tonle Sap Lake with dominant nocturnal rainfall. These diurnal patterns are, however, not clear on some days, and analysis of the synoptic-scale atmospheric condition suggests the effect of the large-scale low-pressure system and disturbances on the appearance of the clear diurnal rainfall pattern. The effect of land-lake and mountain-valley circulations on forming the diurnal rainfall pattern is also implied from ground-observed meteorological data, although further numerical studies are required to examine the detailed mechanisms. The study of local effects on rainfall with consideration of the land-surface dynamics may aid flood and drought management in Cambodia by facilitating a greater understanding of its rainfall pattern. [ABSTRACT FROM AUTHOR]