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dc.identifier.citationStudy of visibility and fog at Malta / J. Wadsworth. London: H.M.S.O., 1930. 23 p.en_GB
dc.description.abstractA statistical survey extending over five years shows that good visibility at Malta is associated with northerly winds, low relative humidity and high barometric ­ pressure. Other favorable factors are the presence of cumulus cloud or alternatively an almost total absence of cloud. The effect of the force of the wind varies according to the wind direction, but in general the visibility deteriorates if the wind becomes strong, especially in easterly winds; yet if the wind is NW and strong the visibility may often be exceptionally good. On summer evenings the visibility at the Observatory in Valletta becomes very good if the wind is from SW and this is regarded as a fohn effect. Diurnal and seasonal effects are also present and the visibility normally becomes good or very good in the afternoon, especially in autumn. The diurnal effect is due to convection, but it tends to be suppressed if the wind is strong or the sky continuously overcast or if the wind blows from SE. Observations of the sea horizon at selected points at various altitudes above sea level indicate that the visibility over t he open sea undergoes a variation which is seasonal but not diurnal ; while the diurnal changes in visibility seawards from Malta are due to the existence of mist or haze in the immediate vicinity of the island. Visibility over the open sea is normally very good in winter with NW. winds and is of the order 30 miles or more. Thick fog is very rare. It is observed over the island in the early morning and less frequently in the evening and also over the open sea in the form of banks or patches. Its frequency at the Observatory is approximately one observation in 18 days in January and February and about half that figure in July and August. It occurs in shallow depressions near a feeble cold front or in regions of light and indefinite barometric gradients in summer; but in the latter case it is also probably a boundary phenomenon between masses of air of different temperatures and humidities.en_GB
dc.relation.ispartofseriesGeophysical memoirs;no. 51
dc.subjectFog -- Forecastingen_GB
dc.subjectVisibility -- Forecastingen_GB
dc.subjectFog -- Maltaen_GB
dc.subjectVisibility -- Maltaen_GB
dc.subjectMeteorology -- Maltaen_GB
dc.titleStudy of visibility and fog at Maltaen_GB
dc.rights.holderThe copyright of this work belongs to the author(s)/publisher. The rights of this work are as defined by the appropriate Copyright Legislation or as modified by any successive legislation. Users may access this work and can make use of the information contained in accordance with the Copyright Legislation provided that the author must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the prior permission of the copyright holder.en_GB
dc.contributor.corpauthorGreat Britain. Air Ministry. Meteorological Officeen_GB
dc.contributor.corpauthorGreat Britain. Meteorological Committeeen_GB
dc.contributor.creatorWadsworth, John
Appears in Collections:Melitensia Works - ERCSciPhy

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