Monday, September 16, 2013

Persistent Stratospheric Warming Setting Stage for Winter

Stratospheric warming currently ongoing throughout this past summer and now is beginning to set the stage for this winter.

This graph shows observed temperatures in the 70 millibar region of the stratosphere from the latitudes of 65N to 90N. The red line illustrates the actual observed temperatures, while the green line shows average temperatures for that time of year. The light gray lines depict the minimum and maximum temperatures observed to this date for any certain time of year. Looking at this past summer, where the red line begins to arch up, we see the observed temperatures were consistently above the green line, meaning the stratosphere has been above normal for a while. It then tapered off for a little while, but as the zoomed-in portion on the bottom right shows, stratospheric temperatures have been on the rise for a bit, to the point where they are above normal.

The temperatures have been above normal for good chunks of the last few months, but the question now is: What is causing these above normal stratospheric temperatures?

An examination around the solar activity reveals daily sunspot trends may be at fault. This chart shows many things at once, but we want to focus on the red line, which shows daily sunspot values. Take a look at the red line after the big spike in the middle of the chart. After that spike, sunspot values take a dive, and stay in slightly below normal territory for a while. This big drop-off happens in the month of June and into early July. Taking a second glance at the stratospheric temperatures, the 70 millibar level was constantly above normal throughout this period of low sunspot numbers. A second example can be found in the time during and right before the big spike on the sunspot graph. These above normal sunspot numbers happened between April and late May. Examination of the temperature chart shows consistently below normal values in this same time frame, meaning there may be a negative correlation between daily sunspot numbers and stratospheric temperatures.

All of that said, if we continue to see the current sunspot numbers stay at unusually low values (circled in blue), the stratosphere should continue to warm. Further warming may set the stage for a warmer than normal stratosphere this winter, which would then encourage a cooler than normal winter.