284
A. Pellegrini et al.
In addition, Zibordi and Frezzotti [29] pointed out that during the 1992/1993
scientific expédition of the Italian National Programme for Antartic Research, the
in-situ observations reported snowfalls (= 20 cm) on 23-24 December and (less
than 5 cm) on 30-31 December 1992. These periods hâve been found also by
analyses, from which it was found that at the following times an RH 70% was
recorded at station 7352:
- from 09:00 on 22 December to 15:00 on 24 December
- from 09:00 on the 30th to 18:00 on the 30th
- from 00:00 on the 31 th to 21:00 on the 31 th
So, considering ail these analyses, was shown to be the used methodology reliable for to establishing the possibility of précipitation in a given period, even if at
présent, estimâtes relative to précipitation amounts are not available, except for a
few cases in the periods when meteorologists live at Terra Nova Bay.
The good agreement between observations and theoretical analysis allowed an
attempt to identify supposed épisodes of snowfall also during the winter, when
direct observation is not possible. As an example, some days in June 1991 were
considered. During winter 1991 a particularly, high snow accumulation was datected by the isotopic and Chemical analyses carried out on a firn core from
Drygalski Ice Tongue and on a snow pit from Aviator Glacier [30].
Applying our methodology, different épisodes of supposed snowfall resulted
during June 1991, in particular from 00:00 UTC on 14 June to 15:00 UTC on 17
June. During this time station 7352 always recorded a relative humidity greater
than 70%; from 03:00 on 14 June to 12:00 on 16 June the station was subject to
warm air masses flowing from the océan, while from 15:00 on 16 June to 15:00 on
17 June the airstreams, blowing down from the Plateau, were dryer and wind
speed was higher. According to the criteria described in Section 4, the latter period can be identified as a blowing/drifting snow épisode.
Therefore, the two situations, (Fig. 10a,b) seem, respectively, to relate to an
épisode of cyclogenesis over the Ross Sea and to blowing snow.
8 Conclusions
In the Victoria Land area and more generally on the Antarctic continent routine
measurements of précipitation amounts using surface-based collection techniques are a difficult task. Many investigators gave different methods of measuring or evaluating précipitation, and many these are summarised and described by
Bromwich [10]. The dominant process affecting précipitation is the advection of
moisture in an air column whose moisture content dépends on température and
altitude. Relative humidity Controls évaporation and précipitation, which both
increase with higher wind speeds.
Beginning with these considérations and analysing the more frequent meteorological conditions that can be found near the base of a steep mountain massif
or, in particular, the prevailing surface winds on Victoria Land, the air masses
with relative humidity greater than or equal to 70% that affect an automatic
weather station on the Priestley Glacier were identified. By analysing the direction
of these airstreams and comparing the periods resulting from the study with the
A. Pellegrini et al.
In addition, Zibordi and Frezzotti [29] pointed out that during the 1992/1993
scientific expédition of the Italian National Programme for Antartic Research, the
in-situ observations reported snowfalls (= 20 cm) on 23-24 December and (less
than 5 cm) on 30-31 December 1992. These periods hâve been found also by
analyses, from which it was found that at the following times an RH 70% was
recorded at station 7352:
- from 09:00 on 22 December to 15:00 on 24 December
- from 09:00 on the 30th to 18:00 on the 30th
- from 00:00 on the 31 th to 21:00 on the 31 th
So, considering ail these analyses, was shown to be the used methodology reliable for to establishing the possibility of précipitation in a given period, even if at
présent, estimâtes relative to précipitation amounts are not available, except for a
few cases in the periods when meteorologists live at Terra Nova Bay.
The good agreement between observations and theoretical analysis allowed an
attempt to identify supposed épisodes of snowfall also during the winter, when
direct observation is not possible. As an example, some days in June 1991 were
considered. During winter 1991 a particularly, high snow accumulation was datected by the isotopic and Chemical analyses carried out on a firn core from
Drygalski Ice Tongue and on a snow pit from Aviator Glacier [30].
Applying our methodology, different épisodes of supposed snowfall resulted
during June 1991, in particular from 00:00 UTC on 14 June to 15:00 UTC on 17
June. During this time station 7352 always recorded a relative humidity greater
than 70%; from 03:00 on 14 June to 12:00 on 16 June the station was subject to
warm air masses flowing from the océan, while from 15:00 on 16 June to 15:00 on
17 June the airstreams, blowing down from the Plateau, were dryer and wind
speed was higher. According to the criteria described in Section 4, the latter period can be identified as a blowing/drifting snow épisode.
Therefore, the two situations, (Fig. 10a,b) seem, respectively, to relate to an
épisode of cyclogenesis over the Ross Sea and to blowing snow.
8 Conclusions
In the Victoria Land area and more generally on the Antarctic continent routine
measurements of précipitation amounts using surface-based collection techniques are a difficult task. Many investigators gave different methods of measuring or evaluating précipitation, and many these are summarised and described by
Bromwich [10]. The dominant process affecting précipitation is the advection of
moisture in an air column whose moisture content dépends on température and
altitude. Relative humidity Controls évaporation and précipitation, which both
increase with higher wind speeds.
Beginning with these considérations and analysing the more frequent meteorological conditions that can be found near the base of a steep mountain massif
or, in particular, the prevailing surface winds on Victoria Land, the air masses
with relative humidity greater than or equal to 70% that affect an automatic
weather station on the Priestley Glacier were identified. By analysing the direction
of these airstreams and comparing the periods resulting from the study with the