How is the hottest month in a calendar year dependent on the lattitude? Is it linear as in, if you go north from the equator the hottest time of the year moves out? Is it the opposite in the southern hemisphere? Why?

Question

How is the hottest month in a calendar year dependent on the lattitude? Is it linear as in, if you go north from the equator the hottest time of the year moves out? Is it the opposite in the southern hemisphere? Why?

In: 6

Answer 1

I wouldn’t count latitude as one of the “important” causes for the lag of the seasons. The main contributor is the fact that the Earth, especially the oceans, are huge “warmth reservoirs”. Anywhere north of the Tropic of Cancer (23.4° N), the day of the summer solstice is the day where the sunlight is bringing in the most energy throughout the year. In the weeks following, however, the solar irradiation is still close to the maximum and still generally contributes to an increase in the “stored warmth”. Only some time later, when the reservoir has more energy in it and the sun has gotten noticeably weaker (lower on the horizon, fewer hours), the situation flips and the sun can’t bring in more stored warmth or even keep up compensating the “leaks” of the reservoir. This lag can be observed pretty much everywhere and is pretty much a worldwide occurrence. In the southern hemisphere it’s shifted by 6 months, in between the Tropics it’s a tad different, but that’s what the Earth’s tilt causes.

Now, there are several factors that determine how strong a specific area is subject to the seasonal lag. How close is a place to an ocean? Are there water or wind currents that amplify or weaken the effect? How is the climate there (is there typically a rainy summer, or droughts…). Are there usually large areas still covered by snow that reflect much of the sunlight until way into the summer?

Now, in regards to your specific question, I’m not aware of an obvious trend suggesting that higher latitudes have more seasonal lag, but I’ve never seen worldwide data. If you know of such a link, I can only speculate. Closer to the equator, the swing of amplitude of the sun’s height over the horizon is smaller –> the seasonal differences in daily hours of sun and in temperature between the seasons is smaller. Smaller differences in energy input would result in less time for the reservoir to catch up.