Прочитайте текст и заполните пропуски A-F частями предложений, обозначенными цифрами 1-7. Одна из частей в списке лишняя.

1. by each region’s polar front jet stream

2. temperatures rose to just above freezing

3. waves develop in the polar front jet stream

4. leading to record-low sea ice coverage

5. the strength of each cold area

6. by weather systems farther south

7. and as the region slips into greater and greater seasonal darkness

In the Arctic, the sea ice melt-off peaks in September A___________ and temperatures fall, sea ice begins to reform. In 2016, however, temperature conditions have been slow to follow this pattern. Instead, near-surface air temperatures in the Arctic have remained warmer than normal throughout Oclober and early November, В_______________ that lags behind the 1981—2010 average extent by almost 2 million square km (roughly 772,000 square miles) for the period.

Cold air at both the top and the bottom of the world is separated from warmer equatorward air C ___________an eastward-moving belt of strong stratospheric winds that separates warm tropical air from cold polar air in the midlatitudes. D______ , or polar vortex, varies with the season, but it is strongest during the winter season in each hemisphere, when the temperature contrast between the pole and the Equator is greatest. In the Northern Hemisphere this week, the presence of a very strong low- pressure system in the North Pacific Ocean has pushed the polar vortex off the Arctic Ocean and into Siberia. Above 80° North latitude, E__________________, some 20 °C (36 °F) above normal on November 15, while temperatures on November 15 over parts of Siberia sank to -40” (which are, coincidentally, equivalent measures on the Celsius and Fahrenheit scales). The polar vortex is typically strong enough to hold its own against most incursions F_______________, but its strength relies on a steep temperature gradienfacross the polar front jet stream — the wall of air separating the polar vortex’s interior from the outside.