Abstract. The Structure des Echanges Mer-Atmosphere, Proprietes des HeterogeneitesOceaniques: Recherche Experimentale (SEMAPHORE) experiment, the third phase of which took place between October 4 and November 17, 1993, was conducted over the oceanic Azores Current located in the Azores basin and mainly marked at the surface by a thermal front due to the gradient of the sea surface temperature (SST) of about 1 ø to 2øC per 100 km. The evolution of the marine atmospheric boundary layer (MABL) over the SST front was studied with two aircraft and a ship in different meteorological conditions. For each case, the influence of the incoming air direction with respect to the orientation of the oceanic front was taken into account. During the campaign, advanced very high resolution radiometer pictures did not show any relation between the SST field and the cloud cover. The MABL was systematically thicker on the warm side than on the cold side. The mean MABL structure described from aircraft data collected in a vertical plane crossing the oceanic front was characterized by (1) an atmospheric horizontal gradient of 1 ø to 2øC per 100 km in the whole depth of the mixed layer and (2) an increase of the wind intensity from the cold to the warm side when the synoptic wind blew from the cold side. The surface sensible heat (latent heat) flux always increased from the cold to the warm sector owing to the increase of the wind and of the temperature (specific humidity) difference between the surface and the air. Turbulence increased from the cold to the warm side in conjunction with the MABL thickening, but the normalized profiles presented the same structure, regardless of the position over the SST front. In agreement with the Action de Recherche Programme te Petite Echelle and Grande Echelle model, the mean temperature and momentum budgets were highly influenced by the horizontal temperature gradient. In particular, the strong ageostrophic influence in the MABL above the SST front seems linked with the secondary circulation due to the SST front. IntroductionInteractions between ocean and atmosphere have been experimentally studied for many years, at scales ranging from the microscale (turbulence) to the synoptic. Many of these experiments focused on the study of physical processes in the marine atmospheric boundary layer (MABL) and of surface turbulent fluxes (e.g., Joint Air-Sea Interactions (JASIN) in 1978 and Humidity Exchange Over the Sea (HEXOS) in 1984). The oceanic mixed layer has also been investigated (e.g., Mixed Layer Experiment (MILE) in 1977). However, the horizontal variability of physical processes in both (atmospheric and oceanic) boundary layers has rarely been experimentally studied; such important variations were revealed for the first time during JASIN, and the Frontal Air-Sea Interaction Experiment (FASINEX), conducted in 1986, was devoted to the study of ocean-atmosphere interactions in inhomogeneous conditions due to the presence of a thermal front in the upper ocean.

Abstract. The sensitivity of the marine atmospheric boundary layer (MABL) subjected to sea surface temperatures (SST) during the Structure des Echanges Mer-Atmosphere, Proprietes des Heterogeneites Oceaniques: Recherche Experimentale (SEMAPHORE) experiment in 1993 has been studied. Atmospheric analyses produced by the Action de Recherche, Petite Echelle, Grande Echelle (ARPEGE) operational model at the French meteorological weather service assimilated data sets collected between October 7 and November 17, 1993, merged with the Global Telecommunication System (GTS) data. Analyses were validated against independent data from aircraft instruments collected along a section crossing the Azores oceanic front, not assimilated into the model. The responses of the mean MABL in the aircraft cross section to changes in SST gradients of about løC/100 km were the presence of an atmospheric front with horizontal gradients of løC/100 km and an increase of the wind intensity from the cold to the warm side during an anticyclonic synoptic situation. The study of the spatiotemporal characteristics of the MABL shows that during 3 days of an anticyclonic synoptic situation the SST is remarkably stationary because it is principally controlled by the Azores ocean current, which has a timescale of about 10 days. However, the temperature and the wind in the MABL are influenced by the prevailing atmospheric conditions. The ocean does not appear to react to the surface atmospheric forcing on the timescale of 3 days, whereas the atmospheric structures are modified by local and synoptic-scale advection. The MABL response appears to be much quicker than that of the SSTs. The correlation between the wind and the thermal structure in the MABL is dominated by the ageostrophic and not by the geostrophic component. In particular, the enhancement of the wind on either side of the SST front is mainly due to the ageostrophic component. Although the surface heat fluxes are not the only cause of ageostrophy, the surface buoyancy flux Qb appears to be an important local source. The data set provides an unprecedented opportunity to analyze the MABL and the oceanic structures of this region. The presence of an oceanic thermal front throughout the period and the occurrence of fairly quiet atmospheric conditions during it permit a detailed investigation of the processes that link lower atmosphere variability to ocean surface forcing. Specifically, these data allow us to address how the wind structure in the lower atmospheric layers is related to the SST and to atmospheric fronts.However, the collected data are often too sparse to conduct such an analysis. A first step of this study consists of dynamical interpolation of collected data through an analysis-forecast system to provide three-dimensional atmospheric and SST gridded fields. For this purpose we have used the so-called 25,047

Eight microwave links operating at frequencies ranging from 6 to 8 GHz and with path lengths ranging from 5.7 to 37.4 km traversing the city of Seoul, Korea are used to detect rainfall and estimate path-averaged rainfall rates. Rainfall detection using rain-induced attenuation (dB) was validated by rain detectors installed at automatic weather stations, and the results confirmed that microwave links can be used to detect rainfall with an accuracy ≥80%. The power-law R-k relationships between rain-induced specific attenuation, k (dB km −1 ), and the rainfall rate, R (mm h −1 ), were established and cross-validated by estimating the path-averaged rainfall rate. The mean bias of the path-averaged rainfall rate, as compared to the rainfall rate from ground rain gauges, was between −3 and 1 mm h −1 . The improved accuracy of rainfall detection led to the improved accuracy of the path-averaged rainfall rate. Hence, it was confirmed that microwave links, used for broadcasting and media communications, can identify rainy or dry periods (rain spells or dry spells) in a way comparable to rain detectors and provide high time-resolution rainfall rates in real time.

In this work, sensible heat flux estimated using a bulk transfer method was validated with a three-dimensional ultrasonic anemometer or surface layer scintillometer at various sites. Results indicate that it remains challenging to obtain temperature and wind speed at an appropriate reference height. To overcome this, alternative observations using an unmanned aerial vehicle (UAV) were considered. UAV-based wind speed and sensible heat flux were indirectly estimated and atmospheric boundary layer (ABL) height was then derived using the sensible heat flux data. UAV-observed air temperature was measured by attaching a temperature sensor 40 cm above the rotary-wing of the UAV, and UAV-based wind speed was estimated using attitude data (pitch, roll, and yaw angles) recorded using the UAV’s inertial measurement unit. UAV-based wind speed was close to the automatic weather system-observed wind speed, within an error range of approximately 10%. UAV-based sensible heat flux estimated from the bulk transfer method corresponded with sensible heat flux determined using the eddy correlation method, within an error of approximately 20%. A linear relationship was observed between the normalized UAV-based sensible heat flux and radiosonde-based normalized ABL height.

The photodegradation of a specific organic pollutant using the Fenton and the photo-Fenton processes has been examined in aqueous solution. The applications of the Fenton process and the photo-Fenton process to the degradation of 2-chlorophenol (2-CP) were investigated. The dependence on the following experimental conditions had been evaluated: initial pH (1.0-9.0), hydrogen peroxide (0.67-2 mM), ferrous ions (0.1-2 mM), initial concentration of 2-CP (0.1-2 mM). The optimal experimental conditions were 1 mM H 2 O 2 , 1 mM ferrous ion and pH 3.0. Under the optimal conditions, the degradation efficiency of 2-CP in the photo-Fenton process was enhanced 4% more than that of the Fenton process. Experimental results about the degradation of 2-CP show that UV irradiation improves the degradation efficiency of the Fenton process. The major intermediate formed during the degradation of 2-CP was pbenzoquinone.