Abstract: Surface and remote-sensing instruments deployed during ESCOMPTE experiment over the Marseille area, along the Mediterranean coast, were used to investigate the fine structure of the atmospheric boundary layer (ABL) during sea-breeze circulation in relation to pollutant transport and diffusion. Six sea-breeze events are analyzed with a particular focus on 25 June 2001. Advection of cool and humid marine air over land has a profound influence on the daytime ABL characteristics. This impact decreases rapidly with the inland distance from the sea. Nearby the coast (3 km inland), the mixing height Zi rises up to 750 m and falls down after 15:00 (UT) when the breeze flow reaches its maximum intensity. A more classical evolution of the ABL is observed at only 11-km inland where Zi culminates in the morning and stabilizes in the afternoon at about 1000 m height. Fine inspection of the data revealed an oscillation of the sea-breeze with a period about 2 h 47 min. This feature, clearly discernable for 3 days at least, is present in several atmospheric variables such as wind, temperature, not only at the ground but also aloft in the ABL as observed by sodar/RASS and UHF wind profilers. In particular, the mixing height Zi deduced from UHF profilers observations is affected also by the same periodicity. This pulsated sea-breeze is observed principally above Marseille and, at the northern and eastern shores of the Berre pond. In summary, the periodic intrusion over land of cool marine air modifies the structure of the ABL in the vicinity of the coast from the point of view of stability, turbulent motions and pollutants concentration. An explanation of the source of this pulsated sea-breeze is suggested.
TL;DR: A classification based on the general flow pattern and on the source intensity evolution along streamlines was proposed, found to be a fairly good fit for the observations and could serve as a tool to better understand and quantify the fluxes at sites subjected to repeatable patterns.
Abstract: A detailed analysis of the various processes at work in stable boundary layers was made. It pointed out that two main mechanisms may affect eddy covariance measurements in stable conditions and that their impacts were different. On one hand, intermittent turbulence produces strongly nonstationary events during which the validity of turbulent transport and storage measurements is uncertain. On the other hand, during breeze and drainage flow events, significant advection takes place and competes with turbulent flux and storage. Intermittent turbulence questions both the ability of eddy covariance systems to adequately capture turbulent flux and storage and the representativeness of the measurements. Ability of the systems to capture the fluxes could be improved by adapting the averaging time period or the high pass filtering characteristics. However, beyond this, the question of representativeness of the flux remains open as the flux measured during an intermittent turbulence event represents not only the s...
Abstract: Numerical studies of sea and lake breezes are reviewed. The modelled dependence of sea-breeze and lake-breeze characteristics on the land surface sensible heat flux, ambient geostrophic wind, atmospheric stability and moisture, water body dimensions, terrain height and slope, Coriolis parameter, surface roughness length, and shoreline curvature is discussed. Consensus results on the influence of these geophysical variables on sea and lake breezes are synthesized as well as current gaps in our understanding. A brief history of numerical modelling, an overview of recent high-resolution simulations, and suggestions for future research related to sea and lake breezes are also presented. The results of this survey are intended to be a resource for numerical modelling, coastal air quality, and wind power studies.
Cites background from "Investigation on the fine structure..."
...... structure of sea breezes and interactions between sea breezes and boundary-layer features, such as lobe and cleft instabilities and horizontal convective rolls (Fig. 5). Observational studies have corroborated the horizontally non-uniform structure and oscillatory propagation speed of the sea-breeze front simulated by models run at high resolution (Yoshikado 1990; Wakimoto and Atkins 1994; Wood et al. 1999; Stephan et al. 1999; Puygrenier et ......
Abstract: The Beijing-Tianjin-Hebei (BTH) region experiences frequent heavy haze pollution in fall and winter. Pollution was often exacerbated by unfavorable atmospheric boundary layer (BL) conditions. The topography in this region impacts the BL processes in complex ways. Such impacts and implications on air quality are not yet clearly understood. The BL processes in all four seasons in BTH are thus investigated in this study using idealized simulations with the WRF-Chem model. Results suggest that seasonal variation of thermal conditions and synoptic patterns significantly modulates BL processes. In fall, with a relatively weak northwesterly synoptic forcing, thermal contrast between the mountains and the plain leads to a prominent mountain-plain breeze circulation (MPC). In the afternoon, the downward branch of the MPC, in addition to northwesterly warm advection, suppresses BL development over the western side of BTH. In the eastern coastal area, a sea-breeze circulation develops late in the morning and intensifies during the afternoon. In summer, southeasterly BL winds allow the see-breeze front to penetrate farther inland (∼150 km from the coast), and the MPC is less prominent. In spring and winter, with strong northwesterly synoptic winds, the sea-breeze circulation is confined in the coastal area, and the MPC is suppressed. The BL height is low in winter due to strong near-surface stability, while BL heights are large in spring due to strong mechanical forcing. The relatively low BL height in fall and winter may have exacerbated the air pollution, thus contributing to the frequent severe haze events in the BTH region.
Abstract: . To investigate the spatiotemporal variability of the mixing layer
height (MLH) on the North China Plain (NCP), multi-site and long-term
observations of the MLH with ceilometers at three inland stations (Beijing, BJ; Shijiazhuang, SJZ; Tianjin, TJ) and
one coastal site (Qinhuangdao) were conducted from 16 October 2013 to 15 July 2015. The MLH of the inland
stations in the NCP were highest in summer and lowest in winter, while the
MLH on the coastal area of Bohai was lowest in summer and highest in spring.
As a typical site in southern Hebei, the annual mean of the MLH at SJZ was
464 ± 183 m, which was 15.0 and 21.9 % lower than that at the BJ
(594 ± 183 m) and TJ (546 ± 197 m) stations, respectively.
Investigation of the shear term and buoyancy term in the NCP revealed that
these two parameters in southern Hebei were 2.8 times lower and 1.5 times
higher than that in northern NCP within 0–1200 m in winter, respectively,
leading to a 1.9-fold higher frequency of the gradient Richardson number > 1 in southern Hebei compared to the northern NCP.
Furthermore, combined with aerosol optical depth and PM 2.5 observations,
we found that the pollutant column concentration contrast (1.2 times) between
these two areas was far less than the near-ground PM 2.5 concentration
contrast (1.5 times). Through analysis of the ventilation coefficient in the
NCP, the near-ground heavy pollution in southern Hebei mainly resulted from
the lower MLH and wind speed. Therefore, due to the importance of unfavorable
weather conditions, heavily polluting enterprises should be relocated and
strong emission reduction measures should be introduced to improve the air quality in
Abstract: In-situ sodar and lidar measurements were coupled with numerical simulations for studying a sea-breeze event in a flat coastal area of the North Sea. The study's aims included the recognition of the dynamics of a sea-breeze structure, and its effects on the lower troposphere stratification and the three-dimensional (3D) pollutant distribution. A sea breeze was observed with ground-based remote sensing instruments and analysed by means of numerical simulations using the 3D non-hydrostatic atmospheric model Meso-NH. The vertical structure of the lower troposphere was experimentally determined from the lidar and sodar measurements, while numerical simulations focused on the propagation of the sea breeze inland. The sea-breeze front, the headwind, the thermal internal boundary layer, the gravity current and the sea-breeze circulation were observed and analysed. The development of a late stratification was also observed by the lidar and simulated by the model, suggesting the formation of a stable multilayered structure. The transport of passive tracers inside the sea breeze and their redistribution above the gravity current was simulated too. Numerical modelling showed that local pollutants may travel backward to the sea above the gravity current at relatively low speed due to the shearing between the landward gravity current and the seaward synoptic wind. Such dynamic conditions may enhance an accumulation of pollutants above coastal industrial areas.
Cites background from "Investigation on the fine structure..."
...Miao et al. 2003; Gilliam et al. 2004; Jamima and Lakshminarasimhan 2004; Harris and Kotamarthi 2005; Puygrenier et al. 2005; Srinivas and Venkatesan 2005), on the strength and the propagation of the sea breeze itself (e.g., Finkele 1998), or on the influence on the sea breeze of particular parameters such as the topography (e.g., Miao et al. 2003) and the coastline shape (e.g., Abbs 1986; Gilliam et al. 2004)....
Abstract: A brief outline of the basic concepts of cloud filtering and atmospheric attenuation corrections used in the Multi-channel Sea Surface Temperature (MCSST) method is given The operational MCSST procedures and products are described in detail The comparative performance of AVHRR-based MCSST'S is discussed via the use of the results of the JPL Satellite-Derived Sea Surface Temperature workshops For the four data periods there is surprisingly good correspondence in the sign and location of the major monthly mean SST anomaly features derived from MCSST's and those from a screened set of ship-based SST's With the partial exception of the one data period severely affected in some areas by volcanic aerosol from El Chichon eruptions, global statistical measures of the MCSST anomalies relative to the the ship data are as follows: biases, 03–04°C (MCSST lower than ship); standard deviations, 05–06°C; and cross-correlations, +03 to +07 A refined technique in use with NOAA 9 data in 1985 has yielded consistent biases and rms differences near −01°C and 05°C, respectively
Abstract: The split window method is successfully being used to retrieve the temperature over sea surfaces from satellite radiances in clear sky and has the great advantage of simplicity. However, such a method does not work over land surfaces, mainly because the emissivity is not equal to 1 and depends on the channel. An extension of this method to apply to land surfaces requires one to take account of emissivity—such an extension is presented in this paper. First, using Lowtran 6, the accuracies of the various linearizations of the radiative transfer equation leading to the split window are checked. This implies that the retrieved surface temperature depends linearly on emissivities and brightness temperatures. Such behaviour has been checked on actual examples. Theoretical equations are then derived which show that the actual surface temperature can again be expressed as a linear combination of the brightness temperatures measured in two adjacent channels with coefficients depending on spectral emissivi...
Abstract: The spatial variation of both the thermal emissivity (8-14 microns) and Normalized Difference Vegetation Index (NDVI) was measured for a series of natural surfaces within a savanna environment in Botswana. The measurements were performed with an emissivity-box and with a combined red and near-IR radiometer, with spectral bands corresponding to NOAA/AVHRR. It was found that thermal emissivity was highly correlated with NDVI after logarithmic transformation, with a correlation coefficient of R = 0.94. This empirical relationship is of potential use for energy balance studies using thermal IR remote sensing. The relationship was used in combination with AVHRR (GAC), AVHRR (LAC), and Landsat (TM) data to demonstrate and compare the spatial variability of various spatial scales.
Abstract: Terms in the budgets of turbulence kinetic energy, temperature and humidity variances, and temperature and humidity fluxes have been evaluated for a baroclinic, convective boundary layer using data obtained from the NCAR Electra aircraft during the Air Mass Transformation Experiment (AMTEX). Although the mean temperature and momentum budgets, which were also evaluated, are strongly influenced by the horizontal temperature gradient, the second-moment budgets are little affected. The mean momentum budget is not well balanced, probably due to a combination of neglect of horizontal advection (aircraft advection measurements are shown to be statistically unreliable) and error in the surface geostrophic wind. For the most part, the measured terms in the second-moment budgets agree with previous estimates. Turbulence dissipation, however, was systematically less than that found in previous tower-based experiments. We find that over most of the mixed layer the temperature variance is maintained by turbul...
Abstract: The advance inland of the sea-breeze past Lasham, 45 km from the south coast of England, has been measured over a period of twelve years. In this time 76 sea-breeze fronts passed Lasham, 36 passed Reading and 12 reached Harwell, 85km from the coast. the rate of advance from Lasham to Harwell in calm or light offshore winds was close to 3 ms−1, and the latter station was passed after sunset at a mean time of 2105 GMT. With onshore winds fronts only appear 30 or 40 km inland, and some fronts may be modified by effects due to the east coast. In some cases detailed measurements were made using pilot balloons, an instrumented motor-glider and radar. the fronts were shown to have raised heads about twice the depth of the following flow and within the heads dry patches occur. Variable secondary flows are inferred and comparison with water-tank models shows that several dynamical features in the tank and in the atmosphere are similar. Measurements support the picture of the development of the front during the day as a gravity current, and theoretical rates of advance are deduced. the observed acceleration of the front in the late afternoon is explained in terms of the increased temperature contrast at the front due to the decrease in solar heating of the sea-air. Shortly before sunset, a sea-breeze vortex may be detached from the rest of the flow. In a case study, it is shown that friction at the upper surface is at least five times that at the ground, and heat and humidity budgets are given for the detached vortex.