Experimental study of the surface marine atmospheric boundary layer over Aegean Greece

Micrometeorological measurements within the surface Marine Atmospheric Boundary Layer (MABL) took place at the shoreline of island of Karpathos, at the South East end of the Aegean Sea (Karpathio Pelagos), during summer 2012. Α meteorological mast was installed at a distance less than 30m from the shoreline, instrumented with a sonic anemometer and a fast krypton hygrometer at 14.5m height with a sampling frequency of 10Hz, in order to measure the turbulent transport of mass and energy of the surface MABL. At the same mast slow response sensors (1Hz) were also installed providing vertical profiles of wind speed and direction, temperature and humidity at three levels (3, 8 and 12 m). Satellite sea surface temperature images were also obtained. The spacial and temporal scales of the Aegean Pelagos have not been studied in the past while it is expected to present differences compared with those measured over oceans or open seas. It is worth to mention that this study is a follow-up of a previous study which took place during summer 2011 at Skyros island, northern Aegean provided similar measurements but with different fetch. During Karpathos campaign, more than of 120 hours stationary surface MABL observations of near neutral wind flows were recorded. The vertical profiles of temperature reveal the presence of a coastal internal boundary layer, mostly below 8m height. Eddy correlation analysis is used to study the turbulent fluxes of mass and energy. According to first results on the stable MABL, momentum fluxes depend on stability and give increasing values with the wind speed. The estimated values are higher, almost by a factor of two, compared to typical values measured over the ocean. These increased values could be attributed to a developed sea state since wind stress is greater over young and developing wave fields. Sensible heat flux is found to be increased with stability and rather independent from wind speed while moisture flux seems to not be dependent neither to stability or wind speed. Some part of the records present upward heat fluxes under near neutral conditions and mostly for positive sea-air temperature differences, possibly associated with sea spray or mesoscale heterogeneity of the sea surface temperature. Ongoing investigation of the turbulent exchanges is expected to provide a more thorough insight on the coupling processes between the surface MABL and Aegean sea

Flux measurements in the surface marine Atmospheric Boundary Layer over the Aegean Sea, Greece

Micro-meteorological measurements within the surface Marine Atmospheric Boundary Layer took place at the shoreline of two islands at northern and south-eastern Aegean Sea of Greece. The primary goal of these experimental campaigns was to study the momentum, heat and humidity fluxes over this part of the north-eastern Mediterranean Sea, characterized by limited spatial and temporal scales which could affect these exchanges at the air–sea interface. The great majority of the obtained records from both sites gave higher values up to factor of two, compared with the estimations from the most widely used parametric formulas that came mostly from measurements over open seas and oceans. Friction velocity values from both campaigns varied within the same range and presented strong correlation with the wind speed at 10 m height while the calculated drag coefficient values at the same height for both sites were found to be constant in relation with the wind speed. Using eddy correlation analysis, the heat flux values were calculated (virtual heat fluxes varied from −60 to 40 W/m2) and it was found that they are affected by the limited spatial and temporal scales of the responding air–sea interactionmechanism. Similarly, the humidity fluxes appeared to be strongly influenced by the observed intense spatial heterogeneity of the sea surface temperature

Experimental study of the turbulent structure of the surface marine Atmospheric Boundary Layer over the Aegean Pelagos under etesian winds

In order to study the physical processes of the turbulent transportation of mass and energy within the surface Marine Atmospheric Boundary Layer over the Aegean Pelagos, field measurements were conducted on the island of Skyros, mainly under the etesian winds, during summer 2011. Α meteorological mast was installed close to the shoreline, instrumented with fast anemometer (sonic) and hydrometer measuring the three components of the wind, the virtual temperature and water vapor at 10m height with a sampling frequency of 20Hz. At the same mast slow response sensors were measuring wind speed and direction, temperature and humidity at three levels (2, 6 and 10 m). Weak stable to near neutral flows were recorded during the experimental period. The eddy correlation analysis re-vealed the momentum and heat fluxes values which are presented and discussed. The estimated values are related both with stability and wind speed variations

On the link between Indian summer monsoon and the Etesian pattern over the Aegean Sea

The Indian summer monsoon (ISM) is a key factor influencing the eastern Mediterranean climate. During early summer period, the thermal low over Pakistan and northwestern India extends towards the Mediterranean through inner Iraq and Turkey. On the other hand, the Azores high expands eastwards and meets the Balkan high pressure system, forming one common system. Greece lies at the transitional zone between these two pressure systems, where persistent northeasterly wind currents form especially over the Aegean, known as the Etesians. The objective of this study is to investigate the interrelation between the ISM and the Etesian winds over the Aegean Sea during summer for an extended period of 44 years (1958-2001) with the aid of composite and correlation analyses and ERA 40 datasets. More specifically, the study will focus on the ISM activity during and prior to or after ‘Etesian episodes’ in order to determine the extent to which one system may lead another. The present analysis reveals that during enhanced monsoon years two upper level ridges prevail over the greater area of interest, one over western Europe and northern Africa, which is part of the Azores high and a second one over Pakistan region, Persian Gulf and Middle Asia, which extends to the west and connecting to the first one forms a slight trough over Eastern Mediterranean. At lower levels, an intensification of the thermal Asian low as well as of the high pressure system prevailing over western and central Europe is apparent. Concurring with this pattern in upper and lower troposphere, anomalously strong northerlies appear over the Aegean during periods with enhanced monsoon activity, as horizontal surface wind anomalies depict. In agreement with previous studies, mid-level subsidence during excess monsoon rainfall periods is found to be more intense over the Eastern Mediterranean, Iraq, Saudi Arabia and east of the Caspian Sea

The influence of Indian summer monsoon on the climatic regime of Eastern Mediterranean

The objective of this study is to further investigate the ISM impact on the temperature and wind regime of the Eastern Mediterranean region, with the aid of multivariate statistics. For this purpose, the standardized Dynamic Indian Monsoon Index by Wang and Fan (1999) was used for a period of 44 years (1958-2001) along with ERA40 Reanalysis data, including monthly means of surface air temperature and wind at 850hPa with a horizontal resolution of 0.25° latitude x 0.25° longitude. Initially, the correlation maps of the seasonal anomalies of the two variables upon ISM index are computed and subsequently Empirical Orthogonal Function Analysis (EOF) is carried out on individual fields. Under this framework, correlation coefficients between the derived EOF amplitudes and ISM index are calculated and in order to validate the results from the first method, the EOF modes that exhibit high correlation coefficients are compared to the aforementioned correlation patterns. Our results verify that there is correlation between Indian monsoon and the etesian pattern over the Aegean Sea

Investigating the Summertime Low-Level Jet Over the East Coast of the U.S.A.: A Case Study

The vertical structure of the marine atmospheric boundary layer (MABL) and the summertime low-level jet (LLJ) along the east coast of the U.S.A. was studied in the framework of a joint expedition (CBLAST-Low), carried out during the summer of 2003 (31 July-27 August) at Nantucket island, Massachusetts, U.S.A. Analyzing measurements from radiosondes, in-situ and remote sensing systems, it was found that within the lower part of the stable MABL, intermittent and persistent LLJ events were frequently observed. Evidence is presented implying that the analyzed jet case was induced by the interaction of a slow-moving cyclone over north-eastern U.S.A. and the stationary high pressure system over the Atlantic Ocean, as well as by the sloping inversion of the MABL. Focused on a 5-day period of persistent south-westerly (marine) flow, the analysis of sodar and radiosonde data revealed the presence of a stable layer associated with increased static stability just before the emergence of low-level flow acceleration. As indicated by the Richardson number profiles, the increased stability of the lower MABL suppressed turbulence, allowed the decoupling of LLJ from friction, providing a favourable environment for the development of inertial oscillations. Significant amplitudes of inertial motions, which were confirmed by the application of a Hilbert-Huang transform, are associated with the acceleration at the LLJ's core, due to the frontal events and the subsequent frictional decoupling, both leading to a modification of the large-scale flow structure. © 2013 Springer Science+Business Media Dordrecht

A comparative study of the main mechanisms controlling indoor air pollution in residential flats

The relative contribution of the main mechanisms that control indoor air quality in residential flats was examined. Indoor and outdoor concentration measurements of different type pollutants (black carbon, SO2, O3, NO, NO2,) were monitored in three naturally ventilated residential flats in Athens, Greece. At each apartment, experiments were conducted during the cold as well as during the warm period of the year. The controlling parameters of transport and deposition mechanisms were calculated from the experimental data. Deposition rates of the same pollutant differ according to the site (different construction characteristics) and to the measuring period for the same site (variations in relative humidity and differences in furnishing). Differences in the black carbon deposition rates were attributed to different black carbon size distributions. The highest deposition rates were observed for O3 in the residential flats with the older construction and the highest humidity levels. The calculated parameters as well as the measured outdoor concentrations were used as input data of a one-compartment indoor air quality model, and the indoor concentrations, the production, and loss rates of the different pollutants were calculated. The model calculated concentrations are in good agreement with the measured values. Model simulations revealed that the mechanism that mainly affected the change rate of indoor black carbon concentrations was the transport from the outdoor environment, while the removal due to deposition was insignificant. During model simulations, it was also established that that the change rate of SO2 concentrations was governed by the interaction between the transport and the deposition mechanisms while NOX concentrations were mainly controlled through photochemical reactions and the transport from outdoors

Model evaluation of the atmospheric boundary layer and mixed-layer evolution

In the present study, an attempt is made to assess the atmospheric boundary-layer (ABL) depth over an urban area, as derived from different ABL schemes employed by the mesoscale model MM5. Furthermore, the relationship of the mixing height, as depicted by the measurements, to the calculated ABL depth or other features of the ABL structure, is also examined. In particular, the diurnal evolution of ABL depth is examined over the greater Athens area, employing four different ABL schemes plus a modified version, whereby urban features are considered. Measurements for two selected days, when convective conditions prevailed and a strong sea-breeze cell developed, were used for comparison. It was found that the calculated eddy viscosity profile seems to better indicate the mixing height in both cases, where either a deep convective boundary layer develops, or a more confined internal boundary layer is formed. For the urban scheme, the incorporation of both anthropogenic and storage heat release provides promising results for urban applications. © Springer Science+Business Media, B.V. 2007

Air Quality in a Dental Clinic during Er:YAG Laser Usage for Cavity Preparation on Human Teeth—An Ex-Vivo Study

Chemical air pollution in dental clinics consists of the emission of gases and particulate matter (PM), both generated by dental equipment and tooth tissues. One basic application of Erbium Laser devices is cavity preparation on human teeth due to its strong affinity to water and hydroxyapatite. The objective of this study was the evaluation of indoor air quality during the application of an Er:YAG laser, as a dentin removal instrument, in a Dental Clinic. Particulate Matter (PM) was measured using the standard method of EN legislation. In order to measure total Volatile Organic compounds (VOCs), a portable monitor was used. In the first experiment, PM10 and PM2.5 concentrations were increased by approximately 10 and 15 times, respectively. From the second experiment it can be concluded that neither of the measured particle concentrations exceeded the recommended indoor limit values while windows were open, although laser influence was still detectable. Within the limitations applied herein, it was found that Er:YAG laser activity for hard dental tissue removal was associated with high PM and TVOCs concentration values in the working environment, under insufficient or no ventilation. Physical ventilation in the aforementioned setting proved to be an important key factor in improving air quality, as both PM and TVOCs concentrations decreased significantly