<p>Let me try to clarify what I'm really asking: </p>

<p>Imagine that, for whatever reason, the meteorologists and Earth scientists decide to revisit the definitions of the seasons---to define them from scratch based on the current best science (kind of like what the astronomers were forced to do as far as <a href="https://en.wikipedia.org/wiki/IAU_definition_of_planet" rel="nofollow">the definition of a planet</a>). Based on our current best science, would it make sense to identify the winter/spring boundary as the date of final stratospheric warming? Or are there other considerations that are arguably more important---that arguably make more scientific sense as winter/spring demarcators?</p>

<p>My question is not about the history of the concept of the seasons, or about linguistics. I of course realize that the concept of final warming has been discovered only relatively recently, while the concept of the seasons has been around for millennia. I'm asking about <strong>scientific definitions</strong> here, which can and do change as science advances (e.g. Pluto used to be classified as a planet, and now it's not). </p>

<p>(Not that it matters for my question, but: if the science started saying that this is the new definition, the media would start reporting it, and eventually even the public at large would become aware of it. Speaking of which---and yes, sorry, this is off topic---but does anyone have any guesses as to why <em>don't</em> the major media outlets report on the date of the polar vortex breakup, regardless of the definition of the seasons? After all, the public is now quite aware of the polar vortex, given it has been blamed for so many cold spells recently.)</p>

<p><strong>Background</strong></p>

<p>According to the Wikipedia article 'Sudden stratospheric warming',</p>

<blockquote>
  <p>The radiative cycle in the stratosphere means that during winter the
  mean flow is westerly and during summer it is easterly (westward). A
  final warming occurs on this transition, so that the polar vortex
  winds change direction for the warming, however do not change back
  until the following winter. This is because the stratosphere has
  entered the summer easterly phase. It is final because another warming
  cannot occur over the summer, so it is the final warming of the
  current winter.</p>
</blockquote>

<p>Similarly, a <a href="http://ozonewatch.gsfc.nasa.gov/facts/warming_NH.html" rel="nofollow">NASA-affiliated source</a> says that</p>

<blockquote>
  <p>The final warming is the last stratospheric warming of the season.
  After this warming, the stratosphere never recovers to its previous
  state and the vortex breaks up and dissipates. The final warming often
  occurs in March or April. Sometimes the stratosphere never recovers
  from what would otherwise be a mid-winter major warming in January or
  February, and that warming becomes the final warming.</p>
</blockquote>

<p>As far as I understand it, once the polar vortex breaks up, one cannot have sudden large temperature dips (like we are having in the northeastern part of the US <a href="http://nymag.com/daily/intelligencer/2016/03/polar-vortex-is-visiting-nyc-this-weekend.html" rel="nofollow">this weekend of April 2-3, 2016</a>). Thus it would seem that the date of final warming is a good candidate for the official date of the end of "meteorological winter".</p>

<p>However, NOAA defines seasons according to calendar months (see <a href="http://www.ncdc.noaa.gov/news/meteorological-versus-astronomical-summer%E2%80%94what%E2%80%99s-difference" rel="nofollow">here</a>). Meanwhile, the Swedes define the start of spring as "when the average daytime temperature exceeds zero degrees Celsius on seven consecutive days" (see <a href="http://www.thelocal.se/20090313/18200" rel="nofollow">here</a>).</p>

<p>So: purely on the basis of current best science, would it make sense to define the end of winter as the date of the final warming? </p>

<p>Yes, one could not know that it happened until some time after it happened, but my understanding is that this lag is on the order of days, not weeks.</p>

<p>Yes, such a definition would have the consequence that some years, meteorological winter would end in January. But, so what? Some winters do seem to end in January... while the present one lasts into April.</p>

<p>Yes, one cannot define the demarcation between the spring and summer or summer and fall using the polar vortex as a reference. But, so what? There is no reason why each demarcation couldn't be a separate story. Even the fall/winter boundary need not necessarily be defined as the date of the formation of the polar vortex.</p>

<p>(And while we're at it--and I know this is off topic, but still---why don't the media report the date of the breakup of the polar vortex? It seems it would be of interest to people, given the notoriety the concept has received especially the last couple of winters... In fact, is the date reported anywhere?)</p>

CC BY-SA 3.0
2016-04-03T06:21:27.287Z
Because until relatively recently (historically speaking), science didn't even know there was a stratosphere or polar vortex.  Indeed, I'd suspect most don't know about a polar vortex now, and I wouldn't bet much on the majority being able to define the stratosphere.  You can't even detect them without access to sophisticated modern instruments, while the solstices & equinoxes can be accurately determined with e.g. a circle of properly-placed stones.
jamesqf
CC BY-SA 3.0
2016-04-03T10:33:08.227Z
As with most terminological definitions, I suspect it's just a matter of convenience — of statistics, communication, tradition, etc. [This question](http://earthscience.stackexchange.com/questions/2490/equinoxes-and-solstices-start-of-the-season-or-mid-season) is related.
Matt Hall
CC BY-SA 3.0
2016-04-03T13:48:41.137Z
@jamesqf Thank you for your comment. I now addressed it in the (new) introductory paragraph of my question.
linguisticturn
CC BY-SA 3.0
2016-04-03T13:51:38.187Z
@kwinkunks Thanks for the comment. But keep in mind that I am talking about **scientific** definitions here. Also, the thrust is not on the history, but rather something like this: if we didn't have the concept of the seasons up until now, and a proposal appeared that we should introduce them as scientific concepts, do you think that the date of final warming would be the best candidate for the winter/spring demarcation?
linguisticturn
CC BY-SA 3.0
2016-04-03T14:08:32.927Z
You asked why it's not how most people define seasons (a fair question), not whether I thought it was a good idea or not (off topic for this site).
Matt Hall
CC BY-SA 3.0
2016-04-03T15:15:45.443Z
Do the analysis, write the paper, get it submitted, reviewed, and published, and then see what happens.
Andy Clifton
CC BY-SA 3.0
2016-04-03T18:15:14.853Z
I think (though I'm no expert) that the "polar vortex" is a weather driver for the northeastern part of North America, but perhaps not so much elsewhere.  Certainly when folks in the northeast are having cold spells and "sudden large temperature dips", we in the west can be experiencing unseasonable warmth.  We can have, as we did this year, a cold, snowy January, warm, dry February, and return to cold & snow for much of March.  It's also not unheard of to have snow in April, May, June, and early July, and to start the next cycle with snow in late August.
jamesqf
CC BY-SA 3.0
2016-04-03T23:55:54.867Z
@kwinkunks Let me try to clarify what I'm really asking. Imagine that, for whatever reason, the meteorologists and Earth scientists decide to revisit the definitions of the seasons---to define them from scratch based on the current best science (kind of like what the astronomers were forced to do as far as the definition of a planet). Based on our current best science, would it make sense to identify the winter/spring boundary as the date of final warming, or are there other considerations that are arguably more important, that arguably make more scientific sense as winter/spring demarcators?
linguisticturn
CC BY-SA 3.0
2016-04-04T00:17:24.653Z
@jamesqf That is interesting indeed. If the temperature and other weather patterns of most of the non-tropical northern hemisphere are uncorrelated from the presence or absence of the northern polar vortex, that is a strong argument that its breakup would not make much sense as a winter/spring demarcator.
linguisticturn
CC BY-SA 3.0
2016-04-04T00:21:02.890Z
@andy-clifton I am not a meteorologist or an Earth scientist. I was hoping that someone on this stackexchange who *is* one of these will just look at my question and immediately be able to tell me why my suggestion makes no sense (or, less likely, that it indeed makes sense, but that there is at present no incentive to push for an 'official' change).
linguisticturn
CC BY-SA 3.0
2016-04-05T10:43:24.290Z
The idea is quite interesting. There are two practical reasons why I prefer the current definition: (a) If we make long term time series analysis and compare the result with studies performed by other scientist, it is important to have a consistent time series and results that are comparable to the other studies' results. Changing season's definitions every 20 years would lead to the loss of this consistency and comparability. (b) If we predict future weather/climate/air_pollution by models, it is difficult to define winter because we do not know whether the polar vortex is predicted correctly
daniel.heydebreck
<seasons>
Why isn't the date of final stratospheric warming and polar vortex breakup regared as the official end of winter?
linguisticturn
# Why isn't the date of final stratospheric warming and polar vortex breakup regared as the official end of winter?

(Asked by: username_0 on 2016-04-02)

Let me try to clarify what I'm really asking:

Imagine that, for whatever reason, the meteorologists and Earth scientists decide to revisit the definitions of the seasons---to define them from scratch based on the current best science (kind of like what the astronomers were forced to do as far as [the definition of a planet](https://en.wikipedia.org/wiki/IAU_definition_of_planet)). Based on our current best science, would it make sense to identify the winter/spring boundary as the date of final stratospheric warming? Or are there other considerations that are arguably more important---that arguably make more scientific sense as winter/spring demarcators?

My question is not about the history of the concept of the seasons, or about linguistics. I of course realize that the concept of final warming has been discovered only relatively recently, while the concept of the seasons has been around for millennia. I'm asking about **scientific definitions** here, which can and do change as science advances (e.g. Pluto used to be classified as a planet, and now it's not).

(Not that it matters for my question, but: if the science started saying that this is the new definition, the media would start reporting it, and eventually even the public at large would become aware of it. Speaking of which---and yes, sorry, this is off topic---but does anyone have any guesses as to why *don't* the major media outlets report on the date of the polar vortex breakup, regardless of the definition of the seasons? After all, the public is now quite aware of the polar vortex, given it has been blamed for so many cold spells recently.)

**Background**

According to the Wikipedia article 'Sudden stratospheric warming',

> The radiative cycle in the stratosphere means that during winter the
> mean flow is westerly and during summer it is easterly (westward). A
> final warming occurs on this transition, so that the polar vortex
> winds change direction for the warming, however do not change back
> until the following winter. This is because the stratosphere has
> entered the summer easterly phase. It is final because another warming
> cannot occur over the summer, so it is the final warming of the
> current winter.

Similarly, a [NASA-affiliated source](http://ozonewatch.gsfc.nasa.gov/facts/warming_NH.html) says that

> The final warming is the last stratospheric warming of the season.
> After this warming, the stratosphere never recovers to its previous
> state and the vortex breaks up and dissipates. The final warming often
> occurs in March or April. Sometimes the stratosphere never recovers
> from what would otherwise be a mid-winter major warming in January or
> February, and that warming becomes the final warming.

As far as I understand it, once the polar vortex breaks up, one cannot have sudden large temperature dips (like we are having in the northeastern part of the US [this weekend of April 2-3, 2016](http://nymag.com/daily/intelligencer/2016/03/polar-vortex-is-visiting-nyc-this-weekend.html)). Thus it would seem that the date of final warming is a good candidate for the official date of the end of "meteorological winter".

However, NOAA defines seasons according to calendar months (see [here](http://www.ncdc.noaa.gov/news/meteorological-versus-astronomical-summer%E2%80%94what%E2%80%99s-difference)). Meanwhile, the Swedes define the start of spring as "when the average daytime temperature exceeds zero degrees Celsius on seven consecutive days" (see [here](http://www.thelocal.se/20090313/18200)).

So: purely on the basis of current best science, would it make sense to define the end of winter as the date of the final warming?

Yes, one could not know that it happened until some time after it happened, but my understanding is that this lag is on the order of days, not weeks.

Yes, such a definition would have the consequence that some years, meteorological winter would end in January. But, so what? Some winters do seem to end in January... while the present one lasts into April.

Yes, one cannot define the demarcation between the spring and summer or summer and fall using the polar vortex as a reference. But, so what? There is no reason why each demarcation couldn't be a separate story. Even the fall/winter boundary need not necessarily be defined as the date of the formation of the polar vortex.

(And while we're at it--and I know this is off topic, but still---why don't the media report the date of the breakup of the polar vortex? It seems it would be of interest to people, given the notoriety the concept has received especially the last couple of winters... In fact, is the date reported anywhere?)

**Tags:** seasons

> **Comments:**
> **username_1**: Because until relatively recently (historically speaking), science didn't even know there was a stratosphere or polar vortex.  Indeed, I'd suspect most don't know about a polar vortex now, and I wouldn't bet much on the majority being able to define the stratosphere.  You can't even detect them without access to sophisticated modern instruments, while the solstices & equinoxes can be accurately determined with e.g. a circle of properly-placed stones.  
> **username_2**: As with most terminological definitions, I suspect it's just a matter of convenience — of statistics, communication, tradition, etc. [This question](http://earthscience.stackexchange.com/questions/2490/equinoxes-and-solstices-start-of-the-season-or-mid-season) is related.  
> **username_0**: @username_1 Thank you for your comment. I now addressed it in the (new) introductory paragraph of my question.  
> **username_0**: @kwinkunks Thanks for the comment. But keep in mind that I am talking about **scientific** definitions here. Also, the thrust is not on the history, but rather something like this: if we didn't have the concept of the seasons up until now, and a proposal appeared that we should introduce them as scientific concepts, do you think that the date of final warming would be the best candidate for the winter/spring demarcation?  
> **username_2**: You asked why it's not how most people define seasons (a fair question), not whether I thought it was a good idea or not (off topic for this site).  
> **username_3**: Do the analysis, write the paper, get it submitted, reviewed, and published, and then see what happens.  
> **username_1**: I think (though I'm no expert) that the "polar vortex" is a weather driver for the northeastern part of North America, but perhaps not so much elsewhere.  Certainly when folks in the northeast are having cold spells and "sudden large temperature dips", we in the west can be experiencing unseasonable warmth.  We can have, as we did this year, a cold, snowy January, warm, dry February, and return to cold & snow for much of March.  It's also not unheard of to have snow in April, May, June, and early July, and to start the next cycle with snow in late August.  
> **username_0**: @kwinkunks Let me try to clarify what I'm really asking. Imagine that, for whatever reason, the meteorologists and Earth scientists decide to revisit the definitions of the seasons---to define them from scratch based on the current best science (kind of like what the astronomers were forced to do as far as the definition of a planet). Based on our current best science, would it make sense to identify the winter/spring boundary as the date of final warming, or are there other considerations that are arguably more important, that arguably make more scientific sense as winter/spring demarcators?  
> **username_0**: @username_1 That is interesting indeed. If the temperature and other weather patterns of most of the non-tropical northern hemisphere are uncorrelated from the presence or absence of the northern polar vortex, that is a strong argument that its breakup would not make much sense as a winter/spring demarcator.  
> **username_0**: @username_3 I am not a meteorologist or an Earth scientist. I was hoping that someone on this stackexchange who *is* one of these will just look at my question and immediately be able to tell me why my suggestion makes no sense (or, less likely, that it indeed makes sense, but that there is at present no incentive to push for an 'official' change).  
> **username_4**: The idea is quite interesting. There are two practical reasons why I prefer the current definition: (a) If we make long term time series analysis and compare the result with studies performed by other scientist, it is important to have a consistent time series and results that are comparable to the other studies' results. Changing season's definitions every 20 years would lead to the loss of this consistency and comparability. (b) If we predict future weather/climate/air_pollution by models, it is difficult to define winter because we do not know whether the polar vortex is predicted correctly  

---

## 0 answers

