Humans have used the idea of time to mark past experiences and anticipate future happenings. To quantify time, we have traditionally used observable periodic natural phenomena, such as the daily and yearly paths of the apparent sun through the sky and the monthly phases of the moon. The sun is especially important as its uneven heating distribution drives weather systems. The orbital points of the solstices and equinoxes define portions of the year in terms of the solar input into the Earth's energy balance, yielding the so-called astronomical seasons. From the viewpoint of the astronomical seasons, we are in late winter, since astronomical spring will start in slightly more than three weeks with the passage of the Spring (or Vernal) Equinox. Astronomical winter commenced on the Winter Solstice during the third week of December.
Similar to the astronomical seasons, we can define meteorological seasons that are meant to fit our calendar as well as the temperature cycle. These seasons are for meteorological observing and forecasting purposes and they are more closely tied to our monthly civil calendar. With this designation, we are now five days into meteorological spring. The current transition interval, "spring", between the year's coldest and warmest portions of the year can be closely linked to the calendar months of March, April and May. We can also have Winter Outlooks and monthly and seasonal averages and records. This information is useful for agriculture, commerce and other purposes. For a more detailed description of seasons, see Thursday's optional Supplemental Summary Information - Meteorological Seasons.
To be submitted on the lines for Thursday on the Study Guide, Part B, Applications', Week 4 Chapter Progress Response Form, under section B. Daily Summary.