MID-SEASONS

Evening Post, Volume CXXVIII, Issue 12, 14 July 1939, Page 10

MID-SEASONS

WHEN DO THEY FALL?

SOLVING A KNOTTY PROBLEM

EVIDENCE OF RECORDS

Never does a season pass without inquiries being made of ''The Post" as to which months should' be counted as belonging to winter or summer, as the case may be, variations on the theme being questions as to when midwinter or midsummer occurs.

Generally speaking, three months are usually allotted to each of the four seasons in New Zealand —September, October., and November to spring, December, January, and February to summer. March. April, and May to autumn, and June, July, and August to winter. That is a rough and convenient way of apportioning the twelve months of the year to the four seasons, but it is often belied by facts. The shortest day of the year, as most people know, falls on June 22, and the longest day on December 22, but to call those two dates midwinter day and midsummer day respectively is manifestly absurd. Invariably more and worse winter weather is experienced after the shortest day than before it. and more summer weather can be confidentally anticipated after rather than before December 22. The same applies to the Northern Hemisphere, where the seasons are the reverse of what they are in New Zealand. England always has most of her summer after June 22 and the worst winter weather after December 22.

In deciding which are the summer months and which the winter months, and what period of the year one may legitimately call midsummer or midwinter, the main factor to be taken into consideration is'temperature. And not only should air temperatures be considered, but also soil temperatures, the latter having an important bearing on what may be called the feel of the seasons. Of course there are other factors, too, such as the length' of the days,, amount of sunshine, wind direction, etc. All these are part and parcel of what we call the weather, and play their part in determining the seasons, but the main factor is undoubtedly temperature, and more especially, as will be shown, soil temperature. Taking the Wellington meteorological records, the monthly mean temperatures as recorded over a number of years show conclusively that midwinter may be regarded as occurring in July, a month after the shortest day, and that midsummer is a month after the longest day, that is, in January or even February. The mean maximum and mean minimum temperatures also point to the same fact, with a tendency perhaps to make midsummer occur in February rather than in January. From the following comparative table it w,ill be seen that in July both the maximum and minimum temperatures have reached their lowest point, and that they are at their highest in January and February.

SOIL TEMPERATURES.

Considering in the next place the temperatures of the soil, those taken at a depth of one foot reach their minimum in July, and those taken at a depth of three feet a month later. Similarly, the maximum at one foot is reached in January, and the maximum at three feet in February. The mean earth, temperatures, as will be seen from the following table, are for the greater part of the year higher than the air temperatures. During the winter, however, they fall below and take a little time to recover, the air in spring warming up quicker than the ground.

It will be noted, too, that right through the autumn the soil at a depth of three feet is warmer than the soil at a depth of one foot, as it retains the summer baking. The three-feet depth soil temperatures, as regards their maximum and minimum throughout the year, lag about a month behind the one-fool depth temperatures.

From soil temperature consideration, there is no doubt that June, July, and August are the winter months, wiih midwinter towards the end of July. December, January, and February are similarly indicated as the summer months, although there is no marked fall in soil temperatures until March, Both air and soil temperatures, therefore, pretty well agree as to winter and summer months, and as to when midwinter and midsummer occur.

MANY OTHER FACTORS. Other factors, however, play a part, although a smaller one, in delermin-

ing the seasons. The average number of ground frosts in Wellington is 2.8 in May, 5.4 in June, 7.8 in July, 6.7 in August, 3.1 in September, and 1.3 in October. This again points to July as being the midwinter month. There is on the average less sunshine recorded in June than in any other month. This is partly accounted for by the fact that the days are at their shortest in that month. But July, even with its lengthening days, only averages three hours more sunshine than June. By August, however, there is a substantial increase in the average amount of sunshine.

The annual rainfall in Wellington is fairly evenly distributed throughout the year and has little effect in determining the seasons. July, however, is on the average the wettest month of the year, with June a close second.

Whether winds are north or south in direction naturally affects temperatures. During winter months fierce southerlies are more probable than in summer months (although they occur at all times of the year unfortunately), and northerlies are more frequent in spring and summer than in winter.

If all these factors are taken into consideration, it is quite obvious that June, July, and August have vindisputed right to be called the winter months, with midwinter towards the end of July. The summer months are perhaps not so well marked off as the winter months. January and February are certainly summer months, and average figures give December and March the right to be called summer months too. although by March the days are getting noticeably shorter. But as far as "weather" in the general sense is concerned, summer usually extends into March.

Of course no single date can be accurately ascribed to midwinter or midsummer. All that can be said with any degree of certitude is that these occur at certain times of year—midwinter most definitely towards the end of July, and midsummer, not quite so definitely, in January or February.

But half the fun of the-weather, and the bane of the meteorologists, is the way in which it delights in indulging in vagaries and going contrary to expectations and averages. The seasons refuse to be tied by time-tables or to abide by averages. If they always kept to the rules, perhaps such questions as those which prompted the writing of this article Avould not be asked with such frequency and regularity.

Jan. Veil. Miiv. April .May June July Au«. Sept. Oct. Nov. Dec. Mt'<\ii daily max. torn)). <iP.:i (!0.S «(",.!) • C2.i» 58.:! . ni.x -,?,. 1 r,4.s ...... tiO.i (i.J.L' GO." Mean M<»itn ilnily tfiiitiliiin. tump, for month. ."..">. 7 01.7 r.r..s (il.ti ."ii.:-! r,ii.2 51.U ' oli.2 47.2 "i2..1 -14.1 49.4 12.4 -17.7 42.5 48.4 15.7 51.2 •is. 4 •"»::.(! T,i)M 5ti.l D3.S r.0.5

Hoi! Tt'iiineraiure. One foot. Tlivoe feet. January t>-~>.-i l!t-(i February fio.l (J.'i.S Man'ii 0:1.0 (i2.S April "iS.-l i'.O.-J vi.sy r.2.ii "). I! .him; -1S.-2 .".I.:! Inly l."..s -IN.:. August. 4ii.S 17. !i Si'i>ii-ml)(.'r -lil.i; -t'.i.S <>,.|.,ln.|- .VI.7 .V2. I NovoiiiIkt -"S.!< ■".;.(» iici-ctiiiii'i- ii:;. 1 lio.i;