In this section, we are going to do two things. First, we are going to discuss when on average we can expect to see the lowest (minimum) and highest (maximum) temperatures each day. Second, we are going to look at a global isotherm map for two different times of the year.

The daily cycle of incoming solar radiation and outgoing radiation from earth produces a predictable daily pattern in regards to temperature. Note: This is an average daily cycle and does not take into account cloud cover or certain weather patterns. In the following video I explain this daily average cycle.

The annual cycle of temperature is similar to the daily cycle in that it, too, has a lag between high sun and high temperature. In the annual case there is about a 30-40 day lag. Subsequently, January and July are the coldest and hottest months of the year throughout most of North America and the world. If you recall, we receive the least amount of solar energy in December and the most in June. However, in Indianapolis, it is January 29 and July 19 that are the days with the lowest and highest average daily temperatures because of this lag.

World temperature maps usually show the January and July patterns of temperature because those months represent temperature extremes. So let's look at some patterns observed in the global isotherm maps for January and July. An isoline that connects all points of highest mean temperature on a world map is called the thermal Equator.