Thursday, September 6, 2012

How Are We Doing So Far?

This is a question that quite often comes from those who have been following our cruise and the many facets of our work at sea.  The answer is that the cruise is going very well now.  We are at station 16 and in 24 hours should be at station 18. To date, we have been completing about 3 stations per day in weather that has been very workable. We have completed 12 MOCNESS tows, 23 CTD casts, 19 VPR casts, 14 Reeve Net tows, and 7 HammarHead (broad-band acoustics) tows.

Map showing our trackline and station positions on top of a plot of satellite-derived sea surface temperature (shown in color) and bathymetry (black contours). We should be starting work at station 18 (circled) just before midnight on 6 September. The cruise is now scheduled to end in Port Hueneme, north of LA, rather than in San Diego as originally planned due to a change in the schedule of the next cruise.

We have been fortunate to have our work area under a very large high pressure system, so winds over 20 knots have been almost non-existent. As a result waves and swell have been moderate, although the very strong low pressure center over Alaska, the remnant of Typhoon “Saola,” could produce some large swells that we may experience in a day or so. To anticipate the weather and make our plans for the next few stations, we frequently check a NOAA website that provides National Weather Surface radiofax charts for the Northeast Pacific and North Pacific, which is where the pressure field charts shown below came from.

24, 48, and 96 hour forecasts of the surface pressure fields over the North Pacific for 6 September 2012. The Pentagram shows approximately where we expect to be at each of these time points in relation to the large high pressure area in the eastern part of the North Pacific.

Our primary interest is in the surface pressure field predictions 24 to 96 hours in the future because the juxtaposition of the lows and highs provide a good measure of the weather coming our way.  Other charts are also available that provide complementary information such as wind-wave charts and sea surface temperatures. As is evident in the charts shown above for 48 and 96 hours, our anticipated position for those time periods should have us still under the influence of the high and in decent working conditions. In the movie below you can see that the ship is rolling around in the swells a little more than in previous days, but overall conditions continue to be favorable.

Peter Wiebe

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