Tuesday, August 10, 2010
Touching on Alison's post which presents a shocking graphic image of Russia enduring the worst heat wave in its recorded and verbal history, it's worth looking at other regions. In this case, the Atlantic Main Development Region (MDR) for hurricanes is offering up July 2010 as the warmest July on record.
Dr. Jeff Masters at the Weather Underground did all the heavy lifting, analyzed the data from the UK Hadley Centre and discovered that July 2010 was the six straight warmest month on record in the region.
As you can see from the NOAA/NESDIS graphic above (click to enlarge), the departure from normal is over 1 degree C for the region. In fact, it is 1.33 degrees C above average for this past July breaking a previous record set in July 2005.
Pinpointing the reasons for this anomaly might appear simple, however there are a lot of factors at work. The North Atlantic Oscillation is one of the prime culprits along with the Arctic Oscillation. The NAO is not something new to climate science. It is one of the most well-known climate variables we have and knowledge of it reaches back several centuries. What is a little less well-known, and has now become significant, is the Arctic Oscillation and the effect it has on climate and the power to drive the NAO.
Another issue is the weakened Bermuda high. Winds flowing out of that high are unusually weak (and are forecast to remain that way). This has the effect of reducing the mixing which occurs in that area of the ocean. Normally, strong trade winds would cause a certain amount of upwelling bringing cold water to the surface and mixing with the heated surface waters causing a relative lowering of the sea surface temperatures. If that doesn't happen the ocean surface continues to heat up. That in turn causes low pressure to occur as the warmed surface air rises. In short, the ocean is going to ditch it's heat somehow. If the wind which drives surface mixing is not present then the warm air generated by warm surface temperatures will force that warmth upward. With lower seasonal trade winds comes lower upper level wind shear. All of that combined means that the globe's air conditioning system will kick into a higher gear and we have a recipe for hurricane formation.
I did not mention global warming. That is simply because, despite all the speculation, we don't have a firm grasp on what causes the NAO and the AO.
As we slide into August and prolonged higher than average sea surface temperatures it brings one phrase to mind: You ain't seen nothin' yet.
Added: While we're looking at graphics, take a look at the global sea surface temperature anomalies from 9 August 2010 (click to enlarge). See anything scary there?