Impact of the Rhône and Durance valleys on sea-breeze circulation in the Marseille area

Sea-breeze dynamics in the Marseille area, in the south of France, is investigated in the framework of the ESCOMPTE experiment conducted during summer 2001 in order to evaluate the role of thermal circulations on pollutant transport and ventilation. Under particular attention in this paper is the sea-breeze channelling by the broad Rhône valley and the narrow Durance valley, both oriented nearly-north–south, i.e., perpendicular to the coastline, and its possible impact on the sea-breeze penetration, intensity and depth, which are key information for air pollution issues. One situation of slight synoptic pressure gradient leading to a northerly flow in the Rhône valley (25 June 2001) and one situation of a weak onshore prevailing synoptic wind (26 June 2001) are compared. The impact of the Rhône and Durance valleys on the sea-breeze dynamics on these two typical days is generalized to the whole ESCOMPTE observing period.The present study shows by combining simple scaling analysis with wind data from meteorological surface stations and Doppler lidars that (i) the Durance valley always affects the sea breeze by accelerating the flow. A consequence is that the Durance valley contributes to weaken the temperature gradient along the valley and thus the sea-breeze circulation. In some cases, the acceleration of the channelled flow in the Durance valley suppresses the sea-breeze flow by temperature gradient inhibition; (ii) the Rhône valley does not generally affect the sea breeze significantly. However, if the sea breeze is combined with an onshore flow, it leads to further penetration inland and intensification of the low-level southerly flow. In this situation, lateral constriction may accelerate the sea breeze. Simple scaling analysis suggests that Saint Paul (44.35°N, about 100 km from the coastline) is the lower limit where sea breeze can be affected by the Rhône valley. These conclusions have implications in air quality topics as channelled sea breeze may advect far inland pollutants which may be incorporated into long-range transport, particularly in the Durance valley.     

Mapping and monitoring of urban landuse of Hisar Town,Haryana using remote sensing techniques

Aerial photographs for the year 1965 and 1975 and Landsat TM (FCC) 1986 data on 1:50,000 scale were used to map and monitor the pattern of growth and development of Hisar Town during the last 20 years. The different landuse categories identified are residential, commercial, industrial, recreational, vacant lands etc. The original shape of the town was nucleated one, but presently it is star-shaped, which is due to extension of the urban centre along the radiating roads. It has mainly elongated itself along the Delhi and Rajgarh roads. The presence of Government Livestock Farm (GLF), Equine Breeding Farm and HAU Farm towards North-west of the town has completely checked its growth on these sides. The total residential-cum-commercial area has nearly doubled during 1965–1975 and trebled by 1986. The change in net area under different types of urban land-use categories, described above has also been calculated. Degraded scrub lands and sandy wasteland on the fringes of the town have been identified where further development can be planned to avoid encroachment on good agricultural lands. Recommendations have been given for future urban planning of the town.     

Statistical Characterization of the Flow Structure in the Rhine Valley

The flow structure at the intersection between the Rhine and the Seez valleys nearthe Swiss city of Bad Ragaz has been documented by means of wind and pressuremeasurements collected from 9 September to 10 November 1999 during the MesoscaleAlpine Programme (MAP) experiment. To understand better the dynamics of theageostrophic winds that develop in this part of the Rhine valley, some key questionsare answered in this paper including the following: (i) How does air blow at theintersection of the Rhine and Seez valleys? and (ii) what are the dynamical processes(mechanical or thermal) driving the flow circulations in the valleys? Statistical analysis of the wind and pressure patterns at synoptic scale and at the scaleof the valley shows that five main flow patterns, SE/S, NW/W, NW/N, NW/S, SE/N(wind direction in the Seez valley/wind direction in the Rhine valley) prevail. The SE/S regime is the flow splitting situation. It is mainly driven by a strong pressure gradient across the Alps leading to foehn, even though some nocturnal cases are generated bylocal thermal gradients. The NW/W and NW/N regimes are mechanically forced bythe synoptic pressure gradient (as the flow splitting case). The difference between thetwo regimes is due to the synoptic flow direction [westerly (northerly) synoptic flowfor the NW/W (NW/N) regime], showing that the Rhine valley (particularly from BadRagaz to Lake Constance) is less efficient in channelling the flow than the Seez valley.The NW/S (occurring mainly during nighttime) and SE/N (occurring mainly duringdaytime) regimes are mainly katabatic flows. However, the SE/N regime is also partlyforced at the synoptic scale during the foehn case that occurred between 18 October and 20 October 1999, with a complex layered vertical structure. This analysis also shows that, contrary to what was observed in a broad section of theupper Rhine valley near Mannheim, very few countercurrents were observed near BadRagaz where the valley width is much smaller.     

Impact of salinity on early life history traits of three estuarine fish species in Senegal

The adaptive mechanisms on the early life stages of fishes to hypersaline stress are still poorly understood and probably determine the resistance of a population to disruption, compared with other less plastic species. The Casamance River in Senegal is an ideal location to test the adaptation to salinity as a dam was built in 1998 to exclude saline water intrusion. This lowered the salinity from 70 to 5 upstream and 60 downstream. The salinity influence on the growth in the early life of three West African fish species (Ethmalosa fimbriata, Sarotherodon melanotheron, and Tilapia guineensis) was studied using the width of microstructures in the otoliths and the individual migratory behaviour analysed from strontium (Sr) to calcium (Ca) ratios in the otoliths. The Sr:Ca ratio was quantified along individual transects measured from the posterior edge of the otolith to the core. The fishes were sampled on both sides of the dam that separated water with low salinity upstream from metahaline and hyperhaline water downstream.The results showed that salinity has different influence on the growth of each species. Ethmalosa fimbriata has the highest growth during the first 180 days in the freshwaters, indicating growth inhibition in the hyperhaline areas. For the two other species no growth difference were found. The Sr/Ca ratio varied widely, in Tilapia and Sarotherodon from below the dam. Individual life histories were more heterogeneous than upstream and showed a crossing of the dam for some individuals which could reach half of the fishes analysed. On the contrary in E. fimbriata, despite the large range of salinity, identical Sr/Ca profiles were found both upstream and downstream. This indicated that Sr/Ca ratio was not appropriate to evaluate life history patterns linked to salinity for this specie.     

Validation of IRI-2007 against TEC observations during low solar activity over Indian sector

Published values of Total Electron Content (TEC) measured by ATS-6 are used to assess the latest available IRI-2007 model during solar minimum over Indian sector covering equatorial to low-mid-latitudes stations. The study reveals that during all seasons and at all locations, in general, the TEC predicted by NeQuick and IRI01-corr options provided in the IRI-2007 model shows much better agreement with the TEC observations as compared to those generated by IRI-2001.option. TEC predicted using NeQuick option found to be little more closer to the observation except at equatorial station during daytime, while IRI-2001 option highly overestimates the TEC in all seasons and times.     

Solar activity dependence of ionospheric electron content and slab thickness using different solar indices

Ionospheric electron content (IEC) and slab thickness () data for the period 1977 to 1980 from Lunping (23.03°N; 121.90°E subionospheric) have been examined for their solar activity dependence. Local noontime monthly means as well as values for the 5 QQ days in a month have been examined separately with different solar indices, namely: solar EUV flux (170–190 Å),S _{10.7 cm} flux and sun spot number (SSN) on a seasonal basis. Both IEC and parameters exhibit better correlation with solar EUV andS _{10.7 cm} fluxes than with SSN for all seasons. IEC increases linearly with both EUV andS _{10.7 cm} flux whereas with SSN it shows a distinct nonlinear relationship during all seasons in both monthly mean and 5 QQ days' values. This study indicates that for correlating and predicting the variations (especially the medium term) in the ionospheric parameters, both EUV andS _{10.7 cm} fluxes have an advantage over SSN.     

On The Small-Scale Dynamics Of Flow Splitting In The Rhine Valley During A Shallow Foehn Event

Flow splitting in the Rhine valley has been observed with a transportable wind lidar (TWL) during a shallow-foehn event in the framework of the Mesoscale Alpine Programme (MAP). The Doppler lidar recorded in detail flow splitting, foehn wind gusts, and flow reversal. Such structures have not previously been observed with comparable detail by conventional in-situinstruments. In addition to the TWL, boundary-layer processes have been documented by means of rawinsondes and surface stations. This paper presents an analysis of the processes giving birth to flow splitting between the Seez and Rhine valleys during Intensive Observation Period (IOP) 5 (1–3 October 1999) by combining the collected data with hydraulic theory. The study shows thatthe splitting of the channelled flow is associated with (1) the existence of a stagnation point at the intersection of the Seez and Rhine valleys, and (2) the deflection of the flow by the lateral sidewalls of the valleys.     

Use of a Sodar to Improve the Forecast of Fogs and Low Clouds on Airports

A sodar was deployed at Roissy–Charles de Gaulle airport near Paris, France, in 2008 with the aim of improving the forecast of low visibility conditions there. During the winter of 2008–2009, an experiment was conducted that showed that the sodar can effectively detect and locate the top of fog layers which is signaled by a strong peak of acoustic reflectivity. The peak is generated by turbulence activity in the inversion layer that contrasts sharply with the low reflectivity recorded in the fog layer below. A specific version of the 1D-forecast model deployed at Roissy for low visibility conditions (COBEL-ISBA) was developed in which fogs’ thicknesses are initialized by the sodar measurements rather than the information derived from the down-welling IR fluxes observed on the site. It was tested on data archived during the winters of 2008–2009 and 2009–2010 and compared to the version of the model presently operational. The results show a significant improvement—dissipation times of fogs are better predicted.