Jökull


Jökull - 01.12.2007, Síða 68

Jökull - 01.12.2007, Síða 68
Jónsdóttir and Sveinbjörnsson monitor the migration of a large ice band across the Denmark Strait and into Dýrafjörður, NW-Iceland. A MODIS image from January 25th and an ENVISAT image on the 26th (Figure 6) record the rapid migra- tion of the sea ice under strong winds. During an ice reconnaissance flight on January 28th it became clear that the sea-ice band had been almost entirely pac- ked into Dýrafjörður. It appears that the amount of ice, packed into such a limited space was sufficient to resist melting and create a microclimate within the fjord, as sea ice was forming there while it melted fast in nearby fjords. The next day, winds and tides bro- ught the ice out of the fjord again where it soon melted within the more spacious Denmark Strait. November Through the spring and summer, a long peninsula of spread sea ice remained fairly close to Iceland (Fi- gure 7). It was not until September 21st that no sea ice was observed along our survey line (Figure 3). ENVI- SAT images show that the sea ice lingered close to Scoresbysund throughout the year, growing rapidly in the early autumn (Polar View, 2007). A comparison between the last six years at a similar date at the be- ginning of winter shows that the ice extent was consi- derably higher in 2007 than during the previous years (Figure 8). The sea-ice extent was very low in 2002, due to the mild weather conditions in the Greenland Sea earlier that autumn. On November 18th a blocking high pressure sys- tem started developing SW of Iceland. After a short spell of strong northeasterly direction, the wind tur- ned to SW. The situation from January was repeated, a low pressure system formed off East Greenland, de- epening and increasing westerly windflow in Den- mark Strait. Negative pressure difference between Scoresbysund and Bolungarvík remained until No- vember 23rd, but not as strong as in January (Figure 9). Subsequently, the wind turned northeasterly again and the high pressure system disappeared. Earlier in November, the pressure difference had also been ne- gative, which no doubt explains why the ice edge was so close to Iceland most of the month. During this time, the sea ice was again driven over to Iceland and came within 18 nm of the coast (Figure 10) before the easterly winds drove the ice away. CONCLUSIONS Sea-ice conditions during 2007 have revealed that de- creased amount of sea ice in the Northern Hemisphere is no guarantee for ice-free waters around Iceland. Blocking high pressure systems have brought the ice to the coasts even if the amount of ice in the region was relatively small. The most extreme cases, in Ja- nuary and November 2007, were generated by unusu- ally high pressure difference between Scoresbysund and NW-Iceland with prevailing westerly winds un- der which the sea ice reached the Western Fjords in a few days. As winter started, ice formation and drift south with the East Greenland current began rapidly. ENVI- SAT radar images show areas of sea-ice formation very clearly as very dark regions (little backscatter), and large patches have been observed on those ima- ges in the Autumn. This interpretation has been con- firmed during an ice reconnaissance flight. Initial fluxes of sea ice into Icelandic waters usu- ally consist of spread ice or long and narrow bands. Open access to detailed satellite images, such as radar images or medium resolution optical images, is there- fore essential in order to detect and monitor such sea ice in near real time as it can, even in small concentra- tions, pose severe threats to passing ships as well as near-shore fish farming. For sea-ice historians, observations of sea-ice be- haviour in 2007 are quite important, as they revealed scenarios which would have been hard to understand had they existed in earlier accounts, with a single fjord being packed with ice, whilst the neighbouring fjords are more or less ice free. The satellite images collected in 2007 provide a valuable dataset for studying ice drift and ice thermo- dynamics in more detail, thus hopefully improving fu- ture ice models. Acknowledgements The authors would like to thank the Icelandic Coast Guard for co-operation on comparing satellite ima- ges with ice observations on ice reconnaissance fli- ghts, Dr. Þór Jakobsson, Eiríkur Sigurðsson, and Sig- þrúður Ármannsdóttir at the Icelandic Meteorological Office for supplying ice reports and information from 66 JÖKULL No. 57
Síða 1
Síða 2
Síða 3
Síða 4
Síða 5
Síða 6
Síða 7
Síða 8
Síða 9
Síða 10
Síða 11
Síða 12
Síða 13
Síða 14
Síða 15
Síða 16
Síða 17
Síða 18
Síða 19
Síða 20
Síða 21
Síða 22
Síða 23
Síða 24
Síða 25
Síða 26
Síða 27
Síða 28
Síða 29
Síða 30
Síða 31
Síða 32
Síða 33
Síða 34
Síða 35
Síða 36
Síða 37
Síða 38
Síða 39
Síða 40
Síða 41
Síða 42
Síða 43
Síða 44
Síða 45
Síða 46
Síða 47
Síða 48
Síða 49
Síða 50
Síða 51
Síða 52
Síða 53
Síða 54
Síða 55
Síða 56
Síða 57
Síða 58
Síða 59
Síða 60
Síða 61
Síða 62
Síða 63
Síða 64
Síða 65
Síða 66
Síða 67
Síða 68
Síða 69
Síða 70
Síða 71
Síða 72
Síða 73
Síða 74
Síða 75
Síða 76
Síða 77
Síða 78
Síða 79
Síða 80
Síða 81
Síða 82
Síða 83
Síða 84
Síða 85
Síða 86
Síða 87
Síða 88
Síða 89
Síða 90
Síða 91
Síða 92
Síða 93
Síða 94
Síða 95
Síða 96
Síða 97
Síða 98
Síða 99
Síða 100
Síða 101
Síða 102
Síða 103
Síða 104
Síða 105
Síða 106
Síða 107
Síða 108
Síða 109
Síða 110
Síða 111
Síða 112
Síða 113
Síða 114
Síða 115
Síða 116
Síða 117
Síða 118
Síða 119
Síða 120
Síða 121
Síða 122
Síða 123
Síða 124

x

Jökull

Beinleiðis leinki

Hvis du vil linke til denne avis/magasin, skal du bruge disse links:

Link til denne avis/magasin: Jökull
https://timarit.is/publication/1155

Link til dette eksemplar:

Link til denne side:

Link til denne artikel:

Venligst ikke link direkte til billeder eller PDfs på Timarit.is, da sådanne webadresser kan ændres uden advarsel. Brug venligst de angivne webadresser for at linke til sitet.