Turbulent Mixing from Extratropical Storm Hermine

Hurricanes and their less intense derivitives (tropical and extratropical storms) are commonly discussed once they reach land due to the devastating impacts they have on coastal (and sometimes not even coastal) communities. However, to truly understand these storms we must look to where they form and generate their power, the ocean.

Hurricanes typically form in tropical regions of the oceans and are fueled by the evaporation of warm water from the ocean surface. As they move across the ocean, they gain strength by pulling more warm moist air from the ocean surface into the storm. The warmer the surrounding ocean, the stronger the storm.

Not only is it interesting to think of the impact of the ocean on the hurricane, but as the hurricane moves up the coast, the strong winds of the storm causes mixing at the sea surface.

In 2016, Hurricane Hermine formed in the Florida Straits in late August and was a Category 1 hurricane when it made landfall in the Florida Panhandle in early September. As it moved inland and up the coast, it weakened to an extratropical cyclone. About a week later it reached New England and passed over the OOI Coastal Pioneer Array.

As it passed over the Pioneer Array, wind speeds at the Inshore Surface Mooring jumped to 18 m s-1 (40 mph!) with heavy rains (high precipitation). On the surface of the ocean, currents doubled in speed, water temperatures dropped, and salinity increased. At the nearby Upstream Inshore Profiler Mooring, warm surface waters were observed to have mixed downwards roughly 45 meters.

Extratropical Storm Hermine passed over the Pioneer mooring array the first week of September 2016. The Inshore Surface Mooring Bulk Meteorology Instrument Package (METBK) at 0 m and a CTD at 7 m captured the response to the storm passage in: 1) an increase in wind speed, 2) an increase in precipitation, 3) an increase in surface current speed, 4) a decrease in sea surface temperature, and 5) an increase in sea surface salinity.

Access Surface Mooring Data

Disclaimer: data used in this example and provided in the .csv file were downloaded from the OOI on July 23, 2020.. The file format and/or contents could have changed if downloaded directly from OOI Net after this date.

Access from OOI Net:

Pull Data Using Python Code. Code demonstrates how to download CTD and Bulk Meteorology data from a Pioneer surface mooring using the Machine-to-Machine (M2M) interface, remove outliers and export the data as a .csv file.

Data Review pages:
Bulk Meteorological Instrument Package
Inshore Surface Mooring CTD

Access Satellite Data

Disclaimer: data used in this example were accessed on Aug 18, 2020. The file format and/or contents could have changed if downloaded after this date.

Access and Plot Satellite SST Data Using Python Code. Code demonstrate how to access Multi-scale Ultra-high Resolution (MUR) satellite Sea Surface Temperature data from the Mid-Atlantic Regional Association Coastal Ocean Observing System (MARACOOS) and make plots during Sept 2016 when extratropical storm Hermine passed over the Pioneer Array.

The decrease in sea surface temperature due to the storm was also captured by Multi-scale Ultra-high Resolution (MUR) satellite SST data. The white diamonds are the locations of the Pioneer Array moorings and the Pioneer Inshore Surface Mooring location is indicated by the black diamond.

The nearby Pioneer Array Upstream Inshore Profiler Mooring captured the downward mixing of warm surface waters below 45 dbar after the passage of the storm. Note the gradually decreased instrument depths on the 6th as the profiler struggled to operate during the storm event.

Access Profiler Mooring Data

Disclaimer: data from the Upstream Inshore Profiler Mooring were downloaded from the OOI with the Inshore Surface Mooring on July 23, 2020. Data can be pulled and exported as a .csv file using the same Python code.

Access from OOI Net:

Plot Wire-Following Profiler Data Using Matlab Code. Code demonstrates how to graph wire-following profiler data from a .csv file.

Upstream Inshore Profiler Mooring CTD Data Review

Pioneer Array Inshore Surface Mooring

Location: On the inner Continental Shelf off the coast of New England in the Mid-Atlantic Bight
Lat/Lon: 40.3619°N, 70.8783°W
Water Column Depth: 92m
Platform: Surface Buoy, Near Surface Instrument Frame
Bulk Meteorology Instrument Package (METBK-A) – attached to the the Surface Buoy Tower, 3m above the sea surface
CTD (CTDBP-C) – attached to the Near Surface Instrument Frame, 7m below the sea surface

Pioneer Array Upstream Inshore Profiler Mooring

Location: On the inner Continental Shelf off the coast of New England in the Mid-Atlantic Bight
Lat/Lon: 40.365°N, 70.77°W
Water Column Depth: 95m
Platform: Wire-Following Profiler
CTD (CTDPF-K) – attached to the wire-following profiler

Graphics Credit: OOI Cabled Array program & the Center for Environmental Visualization, University of Washington

Essentials of Oceanography Textbook Sections

5.4 Why does seawater salinity vary?
5.6 How does seawater salinity vary at the surface and with depth?
6.5 How does the ocean influence global weather phenomena and climate patterns?
16.4 What changes are occurring in the oceans as a result of global warming?

For more details, check out the full “Textbook Crosswalk”

Related Publications

Freilich, M., et al. 2020. Hurricane Dorian Impacts on Northeast US Shelf Marine Hydrography and Ecosystem. Ocean Sciences Meeting Poster. CP44H-3738.

Gawarkiewicz, G. and A.J. Plueddemann. 2020. Scientific rationale and conceptual design of a process-oriented shelfbreak observatory: the OOI Pioneer Array. Journal of Operational Oceanography 13(1):19-36. https://doi.org/10.1080/1755876X.2019.1679609.

Glenn, S.M., et al. 2016. Stratified coastal ocean interactions with tropical cyclones. Nature Communications 7:10887. https://doi.org/10.1038/ncomms10887.

Mann, M.E. and K.A. Emanuel. 2006. Atlantic hurricane trends linked to climate change. Eos 87(24):233-241. https://doi.org/10.1029/2006EO240001.

Goldenberg, S.B. 2001. The Recent Increase in Atlantic Hurricane Activity: Causes and Implications. Science 293(5529):474-479. https://doi.org/10.1126/science.1060040.

Leipper, D.F. 1967. Observed Ocean Conditions and Hurricane Hilda, 1964. Journal of Atmospheric Sciences 24(2):182–186. https://doi.org/10.1175/1520-0469(1967)024<0182:OOCAHH>2.0.CO;2.