Early Season in the Mid Atlantic

One purpose of this blog is to catalog our observations as the hurricane season progresses. In the Mid Atlantic, the challenge for years in the operational models has been to reproduce the strong 2 layer structure of the summer, the warm and fresh surface layer and the cold and salty bottom layer separated by a very strong thermocline/halocline.

For the glider operators in the Mid Atlantic, here is a quick look at the operational models from the NSF OOI Coastal Pioneer Array.  The purpose is to highlight the complex structures near the shelf break that we see in the region around the Pioneer Array.  First the temperature profiles.  The highlight here is the remarkable agreement between the glider data in blue and the data assimilative RTOFS model in green.  The background 2 layer structure is there with that main thermocline running between 20 m and 40 m – amazing agreement between green model and blue data.  Below 40 m, we see the temperature warm up.  This is a type of bottom intrusion of warm and salty water from offshore.  Glider colleagues at VIMS have been studying these intrusions for years.  Both the blue RTOFS model and the red GOFS model are seeing the intrusion, but the match between blue and green is again remarkable.  Now look at the surface, a thin layer of cool water about 5 m deep.  Definitely need to check the salinity on this.

Below is the salinity.  The main halocline between 20 m and 40 m is again well represented by RTOFS.  The warm water intrusion at the bottom is confirmed to be salty, the signature of warm salty slope water moving up onto the shelf.   And the surface layer is indeed very fresh, so a cool and fresh layer has moved in along the surface.  The source of this water needs to be determined.  It is not in the models, so they might not help us.  Likely first stop is the satellite imagery.

Bottom line message: RTOFS is doing a really good job of getting the main two layer system correct at the Pioneer array, as well as the bottom intrusion of warm salty water from offshore.  RTOFS is doing this without the bias seen in GOFS.  Both ROTFS and GOFS outperform Copernicus in this area as usual.  None of the models are doing well with the cold, fresh surface layer, although GOFS does have some of this feature in the salinity profile.  Further investigation needed to determine the transport pathways for the cold fresh surface water.