Local Climates

Local temperatures vary with the time of day and the season of the year. Because the earth stores heat and releases it at a later time, a phenomenon known as thermal lag, afternoon temperatures are generally warmer than mornings. The lowest daily temperature is usually just before sunrise, when most of the previous day's heat has dissipated. Although June experiences the most solar radiation in the northern hemisphere, summer temperatures peak in July or August due to the long-term effects of thermal storage. Because of this residual stored heat, January and February—about one month past the winter solstice—are the coldest months. It is usually colder at higher latitudes, both north and south, as a result of shorter days and less solar radiation. Sites may have microclimates, different from surrounding areas, which result from their elevation, closeness to large bodies of water, shading, and wind patterns.

Cities sometimes create their own microclimates with relatively warm year-round temperatures produced

Figure 2-1 Sun angles in northern latitudes.

by heat sources such as air conditioners, furnaces, electric lights, car engines, and building machinery. Energy released by vehicles and buildings to the outdoors warms the air 3°C to 6°C (5°F-11°F) above the surrounding countryside. The rain that runs off hard paved surfaces and buildings into storm sewers isn't available for evaporative cooling. Wind is channeled between closely set buildings, which also block the sun's warmth in winter. The convective updrafts created by the large cities can affect the regional climate. Sunlight is absorbed and reradiated off massive surfaces, and less is given back to the obscured night sky.

chitecture, which has evolved over centuries of trial and error, provides models for building in the four basic climate types.

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