RU29 home-bound

At roughly 120 km away from RAMA array 0N 80.5E RU29 turned back for Sri Lanka after the unfortunate loss of its rudder. With an 800 km journey ahead the glider can be estimate to be back on land in a month and a half if we travel at our safe speed of 20 km per day.

Missing Rudder Mystery

RU29 ran into trouble today with the loss of his key piloting point. Initial contact increased glider’s buoyancy with a sharp upward pitch and an extreme port roll. Second contact changed glider’s roll to extreme starboard. Team speculates rudder was eventually lost at the end of second encounter at around 100 meters and surfaced with the help of pump and thruster. No large vessels were reported in area that could have interfered, however, fishing activity seems to be the likely culprit. Test dives followed at 10, 60, then 100 meters. Everything is working fine and roll is back to only a few degrees which means we did not lose glider wings.

RAMA Moorings

Here is the dogleg track from Sri Lanka to Mauritius.  The most northern RAMA mooring on the 81E line is a 4S.  We would have to divert to a dues south path to get near it.

The most southern RAMA mooring on the 67E line is at 12 S, right along our intended path.

Looks like our fly-by of a RAMA mooring will wait for 12S, 67E.

One Salty Situation

European model Copernicus and US Navy model HYCOM seems to show a high salinity tail coming out from Gulf of Oman/Arabian Sea and slowly drifting around Sri Lanka and into the Bay of Bengal. Salinity exceeds 36 psu and extends to 56m (according to Copernicus). This could cause trouble with glider flight patterns especially deep water profiling.

Out with the old in with the new

Today RU 29 (finally) made it out of the Sri Lankan maritime border and is on its way to conquer a whirlwind of a situation. Naval ocean model HYCOM and NOAA ocean model RTOFS (depicted in Google Earth overlay figure below) picked up on an eddy spanning over 250 mi in width 400 mi in length that RU29 must cross in order to reach Mauritius off the coast of Africa. The glider may encounter surface velocities measuring from 0 to 0.3 m/s, with the highest velocities propelling the glider on its projected course.

Sept 11 Sentinel Glider Tour

A first tour of the Hurricane Sentinel Glider Fleet on Sept 11 as Florence was still approaching and a comparison to the operational models.  Note that the data was transmitted over the GTS so it was available for assimilation in the models. All plots were prepared by Maria Aristizabal.

The first picket line is off Africa in the formation zone where the north-south extent is relatively narrow.

TWR Glider SILBO indicates the GOFS models are getting the surface layer quite well. All models miss the colder temperature layer near 100 m, but all are back in good agreement between 150 and 200 m.

Second picket line.  The Caribbean and Tropical Atlantic.

First is the station keeping Navy Glider NG300. GOFS models doing well, especially GOFS 3.1

Next is the AOML Glider SG630 occupying the transect south of PR.  All models agree well.

Then the third picket line protecting the US Mainland.

Gulf of Mexico first.

Navy Glider NG429 is in deepwater.  GOFS models do well in deepwater.

Navy Glider NG288 is on the outer shelf.  Not only do GOFS models do well, GOFS 3.1 even matches some of the curves in the profile.  Data assimilation might be doing very well here.

Now South Atlantic Bight

Skidaway Institute of Oceanography glider PELAGIA.  We have told this story before.  GOFS 3.0 is closest, but it might be for the wrong reasons.  GOFS 3.1 is designed to have more vertical resolution in shallow water, and PELAGIA is definitely in shallow water.

Into the Mid Atlantic Bight.

Here is RAMSES, the UNC glider operated by SIO for the NSF PEACH program.  An early favorite in the reporting.  Here is where GOFS 3.1 shines bright even in shallow water.

Moving north, we find Rutgers glider RU33 running along the shelf break. We are on the deeper side of the shelf.  The Stratification Factor maps showed that both GOFS 3.0 and 3.1 were stratified on the outer shelf, and that is what this comparison demonstrates.

Continuing north to UMass Glider BLUE, we see a complicated structure at mid shelf that no model likes. Copernicus seems to lock onto the profile sooner, near 40 m.

One final step north, we move on to the NSF OOI Coastal Pioneer Glider CP376.  Another profile that no model seems to like, even with this glider in deepwater.  Surface temperatures are off. GOFS 3.1 is good at getting the near surface variation.  Copernicus is good at getting the deep variation.

Isothermal shelf waters and Florence

Florence is approaching Wilmington NC as a category 1 storm according to the National Hurricane Center https://www.nhc.noaa.gov/text/refresh/MIATCDAT1+shtml/140842.shtml

It’s slowed down significantly and is still sitting over warm coastal ocean waters. Glider data profiles from RAMSES to the north of Florence and PELAGIA to the south of Florence in previous posts have shown that the continental shelf of the South Atlantic Bight is isothermal, or uniformly warm from top to bottom. Additionally, with the approach angle of Florence winds look to be downwelling favorable meaning that any cold bottom water on the outer shelf was or is likely being advected offshore, while warm surface water is potentially being advected onshore.

This means that despite vigorous mixing in the coastal ocean there is not likely to be any ocean cooling on the shelf, as there simply isn’t any cold water available to mix to the surface. Bottom temperatures from the European Mercator model show warm bottom temperatures across the entire SAB in contrast to the cold bottom temperatures in the MAB.

Florence has been a slow moving storm over the continental shelf and with little ocean cooling  these warm waters will likely not help weaken the storm.

A new batch of glider profiles are coming in this morning to confirm this, but overall this highlights the large differences in regional coastal ocean water masses and highlights processes that we’ll want to investigate in the coming years to better understand how coastal oceans affect storm intensity ahead of landfall.

Anchors aweigh!

RU 29 has officially left Sri Lanka on August 12, 2018. Operating at a standard safe speed of 20 km per day RU 29 is scheduled to arrive at Mauritius, roughly 4,300 km away, in early March. The glider was granted scientific permission to enter British Indian Ocean Territory and anticipated to come within 50 miles off of the Diego Garcia Atoll. With this mission we will see exactly how well our global forecast models predict the variability in the Indian Ocean and what are the optimal paths for gliders to maximize their forecasting impact among other fascinating scientific discoveries that may occur throughout our journey. Stay tuned.

Hurricane Glider Picket Lines

Here is the evolving figure for the Hurricane Glider Picket Lines.  It was just submitted as a placeholder to the OceanObs19 white paper entitled OceanGliders: a component of GOOS. The final figure is due in October.  Other suggestions welcomed.

Caption:

Hurricane Florence, Isaac and Helene cloudtops (left to right) on September 11, 2018, with NHC best tracks behind each hurricane, NHC probability of tropical storm force winds ahead of each hurricane, and the tails of the diverse fleet of ocean gliders in the picket lines transmitting upper ocean data in near-real time to forecasters.

Gliders NG330 & SG630 in the Caribbean

Now standard glider data/operational model comparison plots for the Caribbean hours ahead of Isaac.  First is Navy Glider NG300 station keeping west of St. Croix.

Second is the NOAA AOML Seaglider SG630 running the north-south transect on the southern side of Puerto Rico.

As we discovered over the last few days, all the operational models are doing fairly well in this region. GOFS 3.1 has been a consistent good performer.

The issue we now want to investigate in the Caribbean is salinity. Our focus for this first week of work has been temperature, to see how we are doing with heat content before the storms arrive.   Salinity has an important impact during the storm, specifically, the fresh water layers we expect to see near the surface that inhibit mixing.