276
A. Pellegrini et al.
- On 17 February the broad-scale cyclonic régime continues, affecting the southwestern Ross Sea. At 03:00 UTC another mesoscale cyclone developed over
Drygalski Ice Tongue (see Fig. 7 from [20] and Fig. 10 from [25]). This cyclonic
circulation moved warmer maritime air toward Terra Nova Bay as revealed by
the 5 °C increase in air température at Inexpressible Island.
- By 06:00 UTC on 17 February a similar cyclone formed over the Plateau to the
west of Terra Nova Bay. As Bromwich and Parish [25] underlined, the Plateau
cyclone developed in a strong baroclinie zone between warm maritime air
advected onto the Plateau by the Coastal cyclone and cold katabatic air blowing
southward along the mountains. The Coastal cyclone propagated northward
along the Victoria Land coast at 18.5 km h'1 and caused high wind speeds at
Cape King for the 6-h period centred at 13:00 UTC on 17 February.
- By 00:00 UTC on 18 February the katabatic wind speed increased in the
Inexpressible Island région and another cyclone had suddenly formed near
Drygalski Ice Tongue.
- By 09:00 UTC on 18 February the katabatic speed at AWS 8905 had declined to
22 m s’1 and the mesocyclone had started to move slowly eastward. Then the
katabatic wind speeds remained at around 20 m s-1 for the next 9 h, and by
18:00 UTC on 18 February the mesoscale cyclone had passed out of the station
array [25]. This is confirmed by the fact that the last period relating to
February 1988 ends at 12:00 UTC on 18 February.
Analysing the relative humidity at station 7352, the following consecutive observations with RH 70% can be individualised:
- From
- At
- At
- From
06:00 on 16 Feb to 15:00 on 16 Feb
21:00 on 16 Feb
03:00 on 17 Feb
09:00 on 17 Feb to 12:00 on 18 Feb
Another period, coincident with one selected with the proposed method,
occurred from 17 to 23 January 1989 and was analysed in [26], This paper
analysed the possible interactions of the summer katabatic flow over Terra Nova
Bay with the moving and developing Ross Sea cyclone.
Using pressure values, winds and the nephanalysis shows that a low with a
developing frontal System was moving eastwards offshore from Adelie Land,
between the 17 and 18 January 1989. Entering the Ross Sea on the 18th, this front
deepened the semipermanent cyclone during the 19th. On the 22nd the pressure
gradient was reinforced on the Southern part of the Victoria Land coast. During
the following 24-40 h the low moved northward into the middle of the Ross Sea,
weakening [26],
Figures 5-8 in [26] show the mesoscale analyses, from which the following
most important phenomena can be observed: (1) the upslope winds with précipitation along the Terra Nova Bay glaciers; (2) the moderate barrier winds in the
McMurdo région and up to Franklin Island; and the katabatic flow restored over
the Nansen Ice Sheet and temporarily at Franklin Island
The snowfall occurring on 17-18 January 1989 has been identified considering
the RH 70% at station 7352; in fact, from ail cases the following ones can be singled out:
A. Pellegrini et al.
- On 17 February the broad-scale cyclonic régime continues, affecting the southwestern Ross Sea. At 03:00 UTC another mesoscale cyclone developed over
Drygalski Ice Tongue (see Fig. 7 from [20] and Fig. 10 from [25]). This cyclonic
circulation moved warmer maritime air toward Terra Nova Bay as revealed by
the 5 °C increase in air température at Inexpressible Island.
- By 06:00 UTC on 17 February a similar cyclone formed over the Plateau to the
west of Terra Nova Bay. As Bromwich and Parish [25] underlined, the Plateau
cyclone developed in a strong baroclinie zone between warm maritime air
advected onto the Plateau by the Coastal cyclone and cold katabatic air blowing
southward along the mountains. The Coastal cyclone propagated northward
along the Victoria Land coast at 18.5 km h'1 and caused high wind speeds at
Cape King for the 6-h period centred at 13:00 UTC on 17 February.
- By 00:00 UTC on 18 February the katabatic wind speed increased in the
Inexpressible Island région and another cyclone had suddenly formed near
Drygalski Ice Tongue.
- By 09:00 UTC on 18 February the katabatic speed at AWS 8905 had declined to
22 m s’1 and the mesocyclone had started to move slowly eastward. Then the
katabatic wind speeds remained at around 20 m s-1 for the next 9 h, and by
18:00 UTC on 18 February the mesoscale cyclone had passed out of the station
array [25]. This is confirmed by the fact that the last period relating to
February 1988 ends at 12:00 UTC on 18 February.
Analysing the relative humidity at station 7352, the following consecutive observations with RH 70% can be individualised:
- From
- At
- At
- From
06:00 on 16 Feb to 15:00 on 16 Feb
21:00 on 16 Feb
03:00 on 17 Feb
09:00 on 17 Feb to 12:00 on 18 Feb
Another period, coincident with one selected with the proposed method,
occurred from 17 to 23 January 1989 and was analysed in [26], This paper
analysed the possible interactions of the summer katabatic flow over Terra Nova
Bay with the moving and developing Ross Sea cyclone.
Using pressure values, winds and the nephanalysis shows that a low with a
developing frontal System was moving eastwards offshore from Adelie Land,
between the 17 and 18 January 1989. Entering the Ross Sea on the 18th, this front
deepened the semipermanent cyclone during the 19th. On the 22nd the pressure
gradient was reinforced on the Southern part of the Victoria Land coast. During
the following 24-40 h the low moved northward into the middle of the Ross Sea,
weakening [26],
Figures 5-8 in [26] show the mesoscale analyses, from which the following
most important phenomena can be observed: (1) the upslope winds with précipitation along the Terra Nova Bay glaciers; (2) the moderate barrier winds in the
McMurdo région and up to Franklin Island; and the katabatic flow restored over
the Nansen Ice Sheet and temporarily at Franklin Island
The snowfall occurring on 17-18 January 1989 has been identified considering
the RH 70% at station 7352; in fact, from ail cases the following ones can be singled out: