tag:blogger.com,1999:blog-4572286363399496963.post6303243802799263889..comments2017-06-26T04:15:12.891-08:00Comments on Deep Cold: Interior and Northern Alaska Weather & Climate: Temperature Skewness MapsRickhttp://www.blogger.com/profile/03946704894714514716noreply@blogger.comBlogger4125tag:blogger.com,1999:blog-4572286363399496963.post-82319816475387993072014-03-18T05:12:27.742-08:002014-03-18T05:12:27.742-08:00Eric,
The "normal" for temperature is a...Eric,<br /><br />The "normal" for temperature is always (as far as I'm aware) given as the mean, under the assumption of normality or non-skewness. What we've shown is that this is a poor assumption in some places and seasons.<br /><br />I would have to dig into the historical data to begin to address your second question. My guess is that the spatial and seasonal patterns of skewness have remained generally similar over time, because they depend on physics of the regional environment, but there will be some important changes due to the PDO phase, etc. Rick has written about this in the past, and gave a talk at AMS last month:<br /><br />http://weather.arsc.edu/Events/LAWS08/Presentations/Thoman.pdf<br /><br />https://ams.confex.com/ams/94Annual/videogateway.cgi/id/26571?recordingid=26571<br />Richard Jameshttp://www.blogger.com/profile/08313902028896263276noreply@blogger.comtag:blogger.com,1999:blog-4572286363399496963.post-23688479873114771032014-03-17T17:33:46.107-08:002014-03-17T17:33:46.107-08:00So is the "normal" usually given in temp...So is the "normal" usually given in temp forecasts the mean or median? I've always assumed it was the mean.<br /><br />How has skewness changed in the last 30+ years? How much of the reported warming in Alaska is due to extreme events causing skewness and thus changing the mean more than the median?Eric Lundellhttp://www.blogger.com/profile/17914784378747801359noreply@blogger.comtag:blogger.com,1999:blog-4572286363399496963.post-30793678765871830702014-03-16T17:52:01.111-08:002014-03-16T17:52:01.111-08:00Eric, I think you are highlighting the difference ...Eric, I think you are highlighting the difference between the mean and what is "normal" for the location. When the distribution is skewed, the two are not at all the same. In general, median is a much better measure of normal than mean - especially for non-Gaussian variables like precipitation, but also for temperature it turns out.<br /><br />Fairbanks actually has little skewness in winter despite a few significantly negative values on the map in the same area. So the mean temperature adequately represents normal.<br /><br />I updated the post with a histogram for Kodiak and a brief comment.<br /><br />One could certainly look at higher moments; the fourth moment is the kurtosis and measures the relative importance of tails versus shoulders of the distribution in causing dispersion. It could be quite an important climatological descriptor.<br />Richard Jameshttp://www.blogger.com/profile/08313902028896263276noreply@blogger.comtag:blogger.com,1999:blog-4572286363399496963.post-68477717788943202142014-03-15T16:45:47.710-08:002014-03-15T16:45:47.710-08:00I've been trying to wrap my head around what t...I've been trying to wrap my head around what this measure if skewness means and it's significance. If a red area means that extreme warm days are more likely than extreme cold days, what does that say about our interpertation of the mean? Here in Fairbanks, the mean daily temp on the first of the year is around -10ºF. But despite the potential for -40 or -50, the map above suggests that we are more likely to have 30 or 40 above temps. So is -10 a valid mean or should we look at the median of (guessing) -8? Perhaps this is all inconsequential for Fairbanks. But the extreme red on Kodiak or at Wainwright should make a difference.<br /><br />And what would cause the red in Kodiak? Kodiak has a small variance compared to the Interior. So any extremes would be more pronounced. A summer emphasis on heat would be due to what? Persistant high pressure?<br /><br />Would any higher moments in the temp distribution mean anything? Eric Lundellhttp://www.blogger.com/profile/17914784378747801359noreply@blogger.com