A possible “Sting Jet” affects Scotland

An area of research concentration and forecast significance for the Ocean Prediction Center (OPC) is on a phenomenon called the “bent-back front” and associated low-level jet or cold conveyor belt found in the southwest quadrant of rapidly deepening extratropical cyclones (aka, bombs). This is a forecast concern for the OPC Atlantic and High Seas desks as these systems create hurricane-force winds and very high seas (sometimes greater than 20 m) in prime fishing grounds and shipping routes in the North Atlantic. The “Sting Jet” is likely a small mesoscale area of enhanced, destructive gustiness associated with this low-level jet.

For those who don’t know, the following is a definition of the sting jet from Browning (2004):

“The most damaging extratropical cyclones go through an evolution that involves the formation of a bent-back front and cloud head separated from the main polar front cloud band by a dry slot. When the cyclone attains its minimum central pressure, the trailing tip of the cloud head bounding the bent-back front forms a hook which goes on to encircle a seclusion of warm air. The most damaging winds occur near the tip of this hook–the sting at the end of the tail.”

What is unclear from the literature is whether the sting jet is just a focused microscale phenomenon within a region of strong mesoscale winds (i.e. embedded horizontal shear zones similar to what has been observered in hurricanes and mistaken for tornadoes). Unfortunately for northernmost Ireland and much of Scotland and England, this region of high wind appeared to reach maximum intensity as it crossed the region. Although not in the area of forecast responsibility for OPC, it is interesting to see observations of this phenomenon as it typically occurs in data-sparse regions.

The 06z surface analysis from the UKMET weather office with the sting jet location circled in red and direction of movement depicted with a blue arrow (image courtesy of Tim Hewson of ECMWF). Click on image to enlarge.

The above zoomed-in surface map shows the approximate location of the sting jet as it approached Scotland. The strongest winds started around 07z and ended about two hours later. Below is an hourly sequence of the SEVIRI RGB Airmass product courtesy of Joseph Sienkiewicz (OPC) showing the evolution of this wind event using surface observations (gusts in red). A PV advection jet is easy to discern punching into the cyclone center. This is evidence of a strong stratospheric intrusion associated with a developing PV anomaly and raises suspicion that it could play a significant role in the development of these sting jets. Click on the images to enlarge.

The SEVIRI RGB Airmass product valid at 0545z on 01/03/12 with surface observations overlaid. The yellow polygon highlights the region of highest wind impact.

The SEVIRI RGB Airmass product valid at 0645z on 01/03/12 with surface observations overlaid. The yellow polygon highlights the region of highest wind impact.

The SEVIRI RGB Airmass product valid at 0745z on 01/03/12 with surface observations overlaid. The yellow polygon highlights the region of highest wind impact.

The SEVIRI RGB Airmass product valid at 0845z on 01/03/12 with surface observations overlaid. The yellow polygon highlights the region of highest wind impact.

The SEVIRI RGB Airmass product valid at 0945z on 01/03/12 with surface observations overlaid. The yellow polygon highlights the region of highest wind impact.

The SEVIRI RGB Airmass product valid at 1115z on 01/03/12 with 1100z surface observations and the 1115z ASCAT HI and OSCAT passes overlaid. The yellow polygon highlights the region of highest wind impact.

As you can see in the above sequence of images, the advection jet moves over most of the polygon in the region identified by Browning (2004) where the sting jet is theorized to exist. It would appear as though there is some downward momentum transport associated with the stratospheric intrusion (advection jet) in the area where you also have some evaporation evident by the degradation of the cloud shield near the hook in this southwestern quadrant. Considering the area of highest winds is broader than the sting jet definition would suggest, I am left wondering if this was more a product of the bent-back front co-located with the strong descent associated with the advection jet and developing PV anomaly.

Regardless, the below image highlights the highest wind gusts observed in the United Kingdom with three impressive observations over 100 mph, although these may have been at slightly higher elevation than surrounding observations.

Wind gusts in the United Kingdom on the morning of 01/03/12. (Image courtesy of Tim Hewson (ECMWF))

For some images of this event, click here.

Reference:
Browning, K.A. (2004). The sting at the end of the tail: damaging winds associated with extratropical cyclones. Q. J. R. Meteorol. Soc. 130: 375-399.

3 thoughts on “A possible “Sting Jet” affects Scotland

    • Scott, I actually read that post just after submitting my post. It was a very interesting phenomenon and it’s nice to see the satellite products getting “air-time” during and after these events.

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