270
A. Pellegrini et al.
of température. Rusin [18] observed that weakening of the flow and the
increase of évaporation from the snow surface in summer associated with the
increase in air température are conducive to an increase in relative humidity,
while the development of winter flow causes its decrease.
- The station that reports minimum monthly relative humidity values is 7352,
where winter values are around 30%, and in summer mean monthly values of
about 60% are recorded.
- Station 7379 results are subject to moister air masses than the others. In fact, at
this site a mean monthly relative humidity value of about 70% is always recorded.
- Considering the annual averages, almost ail stations hâve shown a descending
trend of relative humidity in the past few years.
An analysis of the spatial distribution of the mean relative humidity in 1987-1995
reveals that throughout the year it is characterised by a distinctly expressed zonality and large gradients close to the coast. This conforms to the general prédominance of zonality in the distribution of atmospheric processes and the température régime in the région in question.
4 General Analyses
Bromwich [10] showed that the intensity of cyclonic activity is the key factor governing the amount of précipitation and its variations. Besides this, précipitation
génération in Coastal régions is strongly influenced by the fact that moist maritime air masses, poleward moving, are deflected by the steep marginal ice slopes
to blow parallel to the terrain contours. On Victoria Land, intrusions of moist air
far into the continent are accompanied by southerly winds through a deep tropospheric layer.
Station 7352 is located on the Priestley Glacier and it is often subjected to katabatic winds, blowing from north-northwest to northwest (Fig. 2). Katabatic winds
are due to the cooling of air on the slopes of the ice-plateau and to the conséquent
accélération of this air down the slope under the action of gravity. Local orographie
conditions and, particularly, the shape of the surface of the slope hâve a considérable influence on the strength of katabatic winds [19]. These winds originate in the
interior of the continent and are prevalently dry; therefore when at station 7352 a
high relative humidity is recorded, it can be argued either that air masses hâve a
different origin or that blowing/drifting snow phenomena occur. From these considérations, the relative humidity recorded at station 7352 was analysed first.
Considering the whole time sériés of 3-hourly data from February 1987 to June
1996, we identified the cases in which station 7352 reported relative humidity
(RH) values greater than or equal to 70%. Figure 3 shows the number of consecutive days with relative humidity greater than or equal to 70% at station 7352. The
occurrence of 3-hourly consecutive data ranges from 2 to 52, i.e. from 0.25 to 6.5
consecutive days. An arbitrary sélection of cases lasting a period of time greater
than or equal to 2 days was done as being représentative of well-established phenomena: these cases occurred one time during 1988,1990 and 1994, two times in
1993, four times in 1989 and 1992 and five times during 1991. Considering differ-
A. Pellegrini et al.
of température. Rusin [18] observed that weakening of the flow and the
increase of évaporation from the snow surface in summer associated with the
increase in air température are conducive to an increase in relative humidity,
while the development of winter flow causes its decrease.
- The station that reports minimum monthly relative humidity values is 7352,
where winter values are around 30%, and in summer mean monthly values of
about 60% are recorded.
- Station 7379 results are subject to moister air masses than the others. In fact, at
this site a mean monthly relative humidity value of about 70% is always recorded.
- Considering the annual averages, almost ail stations hâve shown a descending
trend of relative humidity in the past few years.
An analysis of the spatial distribution of the mean relative humidity in 1987-1995
reveals that throughout the year it is characterised by a distinctly expressed zonality and large gradients close to the coast. This conforms to the general prédominance of zonality in the distribution of atmospheric processes and the température régime in the région in question.
4 General Analyses
Bromwich [10] showed that the intensity of cyclonic activity is the key factor governing the amount of précipitation and its variations. Besides this, précipitation
génération in Coastal régions is strongly influenced by the fact that moist maritime air masses, poleward moving, are deflected by the steep marginal ice slopes
to blow parallel to the terrain contours. On Victoria Land, intrusions of moist air
far into the continent are accompanied by southerly winds through a deep tropospheric layer.
Station 7352 is located on the Priestley Glacier and it is often subjected to katabatic winds, blowing from north-northwest to northwest (Fig. 2). Katabatic winds
are due to the cooling of air on the slopes of the ice-plateau and to the conséquent
accélération of this air down the slope under the action of gravity. Local orographie
conditions and, particularly, the shape of the surface of the slope hâve a considérable influence on the strength of katabatic winds [19]. These winds originate in the
interior of the continent and are prevalently dry; therefore when at station 7352 a
high relative humidity is recorded, it can be argued either that air masses hâve a
different origin or that blowing/drifting snow phenomena occur. From these considérations, the relative humidity recorded at station 7352 was analysed first.
Considering the whole time sériés of 3-hourly data from February 1987 to June
1996, we identified the cases in which station 7352 reported relative humidity
(RH) values greater than or equal to 70%. Figure 3 shows the number of consecutive days with relative humidity greater than or equal to 70% at station 7352. The
occurrence of 3-hourly consecutive data ranges from 2 to 52, i.e. from 0.25 to 6.5
consecutive days. An arbitrary sélection of cases lasting a period of time greater
than or equal to 2 days was done as being représentative of well-established phenomena: these cases occurred one time during 1988,1990 and 1994, two times in
1993, four times in 1989 and 1992 and five times during 1991. Considering differ-