What defines the Fall season? Well, if you look it up in a textbook there will be one of two definitions. 1) astronomical Fall is between September 21 and December 21 (plus or minus a day), and 2) climatological Fall encompasses the calendar months of September, October, and November.
From a philosophical point of view, both Fall and Spring are seasons without meaning. They represent the transition period from the warm season (Summer) to the cold season (Winter) - and vice versa. As humans we give them attributes (fall foliage, greenup, breakup, etc.) but they lack the definitive markers that summer and winter have. I have done some preliminary research of alternate definitions of season boundaries but given other time constraints have not made much progress. Do they necessarily need to be equal lengths (90 days)?
Using the definition of Fall as the time period between Summer and Winter, and defining Summer and Winter by their respective peaks and troughs, a midpoint for Fall can be defined. In essence, it represents the date falling exactly between the warmest day of the year and the coldest day of the year.
The following three maps show the climatological date for the climatological midpoints of 1) Fall, 2) Summer, and 3) Winter, based on the 1981-2010 climate normals published by NCDC.
I find the Summer and Winter midpoint maps fairly intriguing but the Fall map is rather uninspiring. Anecdotally, I would define Summer in Interior Alaska as May 25th to August 10th and would define Winter as October 20th to April 20th; but I digress. Perhaps seasons can be grouped according to the climate divisions laid out in Climate Divisions for Alaska Based on Objective Methods by Bienief et al.
We ecologists think of seasonality in term of vegetation and plant growth. Or the lack thereof. Wet or frozen water/snow is often somewhere in there too.ReplyDelete
Summer = vegetation, Winter = none. In between are either getting there or getting done with growth.
Simple stuff until someone with lots of free thinking time committed us to keeping track of things by noting when the sun poked through a crack in a rock somewhere, or by observing the stars or moon cruise around the sky.
Gary, you are certainly correct that from an ecological point of view both Spring and Fall have significant meaning. Just like geological classifications are based on biological markers, perhaps climatological boundaries should be based on something similar; i.e., greenup, breakup, etc.ReplyDelete
Then there's those folks that live on the equator, or Arctic-Antarctica.Delete
One fellow I visit with via radio on South Cook Island notes only a shift in the winds and precipitation to denote seasonality. Boring?
Another at Australia's Antarctic base at Mawson Station notes summer (mid-October-late February)) by when they can finally head north for a warmth break and new crews arrive to conduct research.
In that sense we Alaskans may be fortunate to have a greater contrast to our seasons. Still, I miss the seasonal fall of apples from the tree.
I live on the equator in Quito, Ecuador (over 9000' elevation). Here the weatherman calls it summer in the morning if it is sunny and winter in the afternoon when cold high elevation rain rolls in.ReplyDelete
Excellent info...ah, but on the equator your Sun will be almost directly overhead in a few weeks and it's still warm when the stars come out at night.Delete
In Fairbanks Alaska the Sun (latitude 64 N) never gets 49 degrees above the horizon, and it's very rarely warm when the night stars shine due to almost perpetual daylight during our warm summer "Season", which for all purposes is at an end.
Such are the differences on our wonderful Earth.
For those interested, here's an independent and very interesting summary of annual weather for Quito, EC., and Fairbanks, AK.:Delete
Gary...can't verify the accuracy of the info