Dear Tom,
I define a “hot day” as a day on which the temperature reaches or exceeds 100 degrees. Looking at worldwide temperature readings, I have noticed that hot days occur much more frequently in the Northern Hemisphere’s summer than in summers in the Southern Hemisphere. Why should that be?
James Went,
Rockford

Dear James,
Your observation that 100-degree days occur more frequently at locations in the Northern Hemisphere than at locations in the Southern Hemisphere is correct, but very high temperatures can and do occur “down under.” Australia, for example, records many summer days with readings above 100 degrees. In general, however, high temperatures occur much more frequently and at many more places north of the Equator than south of it. The explanation lies in the ratio of land to oceans. Most of the Earth’s land masses are situated north of the Equator and oceans cover much more of the Earth’s surface south of the Equator. Oceans moderate air temperatures, greatly reducing the occurrence of very hot or very cold temperatures. Intense heat, above 100 degrees, is mainly a characteristic of continental interiors. Consequently, very hot days occur more frequently north of the Equator than south of it.