Using ASCAT Wind and Other Data in Marine Forecasting

5.0 Closing the Case, 25 November » 5.2 Airmass RGB and Polarstern

The Airmass RGB animation from 23 November at 06 UTC to 25 November at 12 UTC shows the movement and progression of the cold front during this period.

The table outlines the changes in in observations from on board the ship. Compare the sea conditions when the Polarstern was east of the cold front and then west of it a day later.

Parameter

06 UTC 24 November 2013

12 UTC 25 November 2013

Wind speed

18 m/s

13 m/s

Wind direction

NW’ly

W’ly

Sea level pressure

982.2 hPa

995.0 hPa

Pressure tendency

Decreasing steadily

Increasing steadily

Atmospheric temperature

2.2°C

-0.9°C

Height of wind waves

4 m

2.5 m

Height of swell

3 m

4.5 m

Weather

Precip within sight

Showers of rain/hail or both

These results fit nicely with the theory of cold fronts and the weather changes that can be expected ahead and behind them.

Looking at the evolution of the cold front, the system was well developed on 23 and 24 November, and lost its intensity by 25 November. This is seen by the structure of the cloud band associated with the cold front on the satellite imagery. It was well formed at the beginning of the period but lost its structure on 25 November after passing over the Polarstern.

The pressure rise measured by the Polarstern between 24 and 25 November is indicative of the cold front having moved over the ship’s position, with an increase of nearly 13 hPa in one day.

The wind direction also shifted from northwesterly as measured when the ship was east of the cold front, to a more westerly wind when it was west of the cold front.

Although the temperature change was not dramatic, it did decrease by about 3°C with the passage of the cold front over the Polarstern.