Warm weather part deux

Previously, I began an investigation into why we have recently had warm weather in December here in Florida, when most of the rest of the country has not. I identified the likely culprit as being a teleconnection between US weather and warm anomalies in the middle of the Northern Pacific. To investigate this further, I decided to use HADSST3 to examine the anomalies (relative to the mean value for all Decembers available) in the region in question, which I estimate to be about 30-50N and 180-208E. Downloading the data from KNMI, I then looked at the years I had identified as probably matching our recent pattern historically (below average US, above average Florida). As it turns out, the average anomaly relative to the long term mean for those Decembers was about .4 K above average, which confirms my suspicion, I think, that our recent pattern has a bit to do with warm water in that region: there is at least some association between warm anomalies there and a pattern of below average temperatures for the US as a whole and above average temperatures for Florida, in the month of December. Of course, this is probably not the only phenomenon that can be associated with a warm Florida and a cold US: at least some of the years I selected had below average temperatures for that region (those that didn’t, had an average anomaly of ~.87K). At any rate, I figure it was worth looking into a couple of additional details. First, the PDO: For the official PDO data, the average December value in the years (excluding 1897, not available) I selected as analogs, was in fact about -0.68 below the long term mean (1900-2012) and the value for the years where there was, in fact, a warm anomaly in the region I selected, was about -1.2 below the long term mean, which confirms that the analog Decembers were generally during negative PDO conditions. In fact, in the subsample of years with actual positive temperature anomalies relative to the long term mean in the selected region, only 1992 had a PDO value for that December above the long term mean; it seems probable that the actual reason for the cold weather in the US that year was the eruption of Pinatubo in 1991, which probably also disrupted the PDO pattern’s connection to weather phenomena somewhat. I think this more or less confirms my diagnosis: a negative PDO (warm central North Pacific Ocean) is teleconnected to warm December weather in the South East US, a link especially strong during La Nina years, but present to a lesser extent, and in  a reduced area, in years without a La Nina. Similarly, a negative PDO is associated with cold weather in December in much of the US, and this is even more true absent a La Nina.

Well, there was one other question my mother had, which was whether there was some connection to solar activity in the reduced temperatures in much of the US. Well, it took a lot of work to get, not much of an answer, honestly. The following shows the average monthly (degrees Fahrenheit) anomaly (blue) and average annual smooth (average of 11 month and 13 month centered averages, black) of USHCN data, in months from date of sunspot minima (data from here, minima determined by lowest value of the average of an 11 month centered average and a 13 month centered average, in a cycle), as well as the average of sunspots over the same periods, minus 64.81525 and divided by 184.91169136522 (red):

SolarCycleUSHCNIt is not obvious to me that there is any instantaneous effect of solar activity on temperatures in the US. Looking closely, it looks as though there might be a delayed effect, although there is a lot of noise. This shows the above, minus the blue curve:

SolarCycleUSHCN2And then with the sunspots shifted to three years later:

SolarCycleUSHCN3Well, okay. So it’s hard to say if there is a relationship: there might be, but the data is very noisy, and it’s hard to detect. But, if there is about a 3 year lag, then since last minima was around 2008, we might still be feeling it’s lingering effects in our cold weather here. Maybe. It’s hard to say.

EDIT: Thinking on it, I remembered how, by removing the effects of long term variations, I was better able to discern the effects of volcanic eruptions on the temperature record. So I used the smoothing technique (10 times!) to take the long term variations out of the temperature data. So this is the new phase plot:

SolarCycleUSHCN4

The new normalization factors for the sunspots are minus 63.1120103092784 divide by 202.857354779726, and I then lag them by 75 months to get the green curve (I also used the averaged cycle lagged 125 months to get the values from before 84 months before minima). That would put us, presently, a little before the full effects of the minima in 2008 would be fully felt, but only a year and four months away. The best fit linear regression coefficient for anomalies on this cycle is  0.516260800957563. This, then, shows the lag short term impact of sunspots (thermal inertia only crudely dealt with by the lag):

USHCNSunspotInfluence

So, I think my answer is, yes, low solar activity might be contributing a little bit to recent cold weather in the US. Of course, the multidecadal impacts of Solar Activity can’t be well resolved by this sort of analysis. Nevertheless the impact does appear to be there, and it is not negligible.

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