Archive for July 18th, 2008

Eye to Eye

Friday, July 18th, 2008

Rick:

When we talked about crossing the Atlantic and flying into Hurricanes 2 years ago, I was originally thinking they would be separate missions.

Now a close-up of the Scarlet Knight and Bertha, side by side.

Getting to know Bertha

Friday, July 18th, 2008

Tropical Storm Bertha's outer cloud bands are starting to pass over RU17.

Bertha's eye should pass by RU17 early tomorrow.

RU17 is pretty much assured of getting tropical storm force winds.

RU17 is already rigges with a modified flight plan with a standard stay deep behavior, the same one we ised to avoid the fishing gear as we crossed the shelf break a couple months ago. Tonight, at the 12 midnight surfacing, Hugh will turn RU17 to the north.  We'll run north with the currents, the winds and the waves.  A following sea.  If we are on the wrong side of the storm for the winds, we are on the right side of the ring for currents.  The currents on this side of the ring are the same direction as the waves.  Just ask anyone here in Hawaii what happens when the currents are opposing the waves.  We just saw it firsthand with today's RU05 deployment.

Bertha Approaches

Friday, July 18th, 2008

Below image shows RU17 flying in the break in the clouds just to the northeast of Tropical Storm Bertha.  In this image, the colors represent sea surface temperatures.  White are the clouds that we can't see through.  RU17 is barely visible in the break, but the break was clear enough to give us a good look at the cold eddy described in the previous posting.

 

NOAA National Hurricane Center has Bertha forecast to track straight to the northeast, right at us.  We should start feeling the effects of Bertha early Saturday morning.

The track is narrowing, with the very highest probability of Tropical Storm winds just a bit to our west.  We are essentially directly in the path of storm.

 The waves are picking up in that region between Bertha and that band of couds to RU17's north.

Hugh completed rigging RU17 for the storm this morning, sending the new flight pattern to the glider at the noon surfacing.  We will fly between 25 m depth and 90 m depth till the storm passes.  Then will go back to our more energy efficient pattern after it passes.

The Google Earth Morning Report

Friday, July 18th, 2008

Its still morning in Hawaii.

Satellite Sea Surface Temperature (below) shows the cold eddy centered along 47 W - a big bonus we found last night. We are heading across the warm waters that are being pulled counterclockwise around this strong feature.

 

Altimetry (below) has us already in the eddy, but currents are slow.  its that space-time thing with altimeters.  The data makes a big difference when the satellite passes overhead, but then you have to wait several days for another overpass.

So the models do the space-time interpolation for you.  Below in the current speed plot the NLOM model says we are heading into the fast swirl velocities associated with the ring.  We have to be a bit cautious, we don't want to fly to deep into the eddy and repeat the events on the trip to Halifax.  On the trip to Halifax, we made a second loop around an eddy, partly because we wanted to try it and we knew we had the battery power to spare.  Here we don't want to do any extra loops we don't have to.  We have already had our eastward progress stopped twice by unfavorable currents on this trip.  In each case we had to find a different route around an eddy.  We will have more of these that we don't expect, so we don't want to do any additional loops on purpose.

 Below is contoured the north/south component of the NLOM currents in green.  That strong band of currents to the north in bright green is out target.

Once in that green region, we head north to 40 N, we we see a lot of red spots in the image below.  The bright reds are strong currents to the east.  That is where we want to be.