Climate Types

Climate Data and Statistics

Many observations are necessary to calculate the statistical properties. Thousands of locations around the world take hourly measurements of temperature, precipitation, wind speed and direction, pressure, and many other atmospheric elements. These measurements are the sources for much of the climate data that scientists use. By focusing on one location over a long period, such as 30 yrs. (years), it is possible to calculate average values for the elements and also examine the variation of these elements over time. For example, the average temperature for November 1 in Boston, Massachusetts, is 13.8 °C (57 °F). If this value is compared with the temperature for individual years, it becomes obvious that some years are cooler, some years are warmer, and, in rare cases, some years may be the same as the average.

Using the same data, it is possible to examine seasonal patterns. When are the cool months, and when are the warm months? Is precipitation evenly distributed throughout the year, or are there any dry and wet periods? If there are wet and dry periods, during which seasons do they occur? To answer these questions, and others, it is necessary to understand some of the statistics that are calculated using atmospheric measurements. The following values are calculated over a long period, such as 30 yrs. The average daily temperature is obtained by adding the minimum and maximum temperatures for a day and dividing by two. Adding all the average daily temperatures during a month and dividing by the number of days results in the average monthly temperature. The average annual temperature is the average of the 12 average monthly temperatures during a year. The annual temperature range is the difference between the warmest average monthly temperature and the coolest average monthly temperature.

Similar values are determined for precipitation. It is important to note that precipitation refers to liquid amounts; any solid precipitation (snow, sleet, freezing rain, and hail) is melted to [Page 466]give a liquid equivalent. Average monthly precipitation is the total precipitation during a month, obtained by adding daily average precipitation amounts. Average annual precipitation is the total precipitation from January 1 to December 31. It is the sum of the 12 average monthly precipitation values.

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