The statements, "Its rainy today." and "It's always rainy in July." emanate from two different concepts. The first refers to the current atmospheric conditions on a particular day. The second indicates an expectation of the weather conditions based on a norm. It is often said that climate is what you expect and weather is what you get! A more geographic explanation is weather is the current condition of the atmosphere over a few days to a few months. This includes factors such as rainfall and temperature. Climate is the average weather conditions of a place over a period of at least 30 years.
Elements of weather:
The Coriolis effect
- Wind is air in motion. Air molecules tend to move from areas of high pressure to low pressure. Theoretically, cold dense air from the Polar regions should blow towards the equator and fill the void where heat warms up the air and causes air molecules to rise and spread out . However, the spinning of the Earth exerts a force on these currents of air, making them deflect to the left in the Northern Hemisphere and to the right in the Southern Hemisphere. This is called the Coriolis Effect. Other local factors affect wind speed and direction such as the uneven heating of the Earth's surface, and the presence of mountains. Winds transport heat and coldness, moisture and dust for great distances and is has a significant influence on weather conditions. Wind speed is measured by an anemometer while wind direction is measured by a wind vane or wind sock.
The Coriolis effect
2. Temperature is the most important determinant of weather and climate since it tends to affect other elements of the weather. Temperature is the degree of hotness or coldness of a place, measured in Degrees Celsius or Fahrenheit. When the Sun heats up the ground during the day, the air in contact with it gets warmed up. As you move further away from the ground, the temperature begins to drop, hence the reason why highland areas tend to be cooler than plains. Temperatures are also affected by proximity to large water bodies, mountains and most importantly, latitudinal positioning (Equator versus the Poles). Temperatures are measured using various types of thermometers and usually given as a mean or average for the day, month or year. Maximum and minimum temperatures are also compared when studying weather and climate.
3. Humidity is the level of moisture in the air. The more water vapour in the air, the higher the humidity. If the humidity level exceeds the amount that the air can hold, then condensation takes place, forming dew if it is warm and frost if it is cold. At higher altitudes, clouds begin to form. Humidity also varies with temperature. Warm air can hold more moisture than cold air. It is important to note that there are two types of humidity - relative humidity and absolute humidity. This element of weather is measured by a hygrometer.
4. Precipitation can be rain, hail, drizzle, sleet snow, fog or mist. It is the collective term given to moisture that falls to the ground from the atmosphere. The water cycle moves water from the oceans to the air by heating, then to the land by precipitation, then back to the sea. Rainfall which is the most common form of precipitation is measured in units of millimeters or inches by an instrument called a rain gauge.
5. Atmospheric Pressure is closely related to wind since wind is air moving from high to low pressure. The greater the difference in pressure, the faster the wind. Atmospheric pressure is the weight of the atmosphere (air) on the surface of the Earth. Low pressure occurs when the Sun heats up the land surface which warms the air in contact with it, exciting the air molecules to spread out and rise as the air parcel becomes lighter. If there is accompanying moisture in the air then condensation will occur when air reaches a certain height and cools. Low pressure systems occur when there is a continuous feed of warm moist rising air in an area. High pressure systems come about when usually cooler dense air sinks. this limits the development of showers and hence more stable conditions prevail. Atmospheric pressure is represented by isobars on a weather map. Atmospheric pressure is measured in millibars by a barometer.
6. Cloud Type and Cover. Cloud cover has an appreciable role in weather description and forecasting. A cloudless or overcast sky is usually a clear indication of weather conditions. Cloud cover is measured in oktas. Cloud type can also signal potentially fair or bad weather. There is a fairly detailed system for determining cloud types but they all fall into three basic categories of high, medium and low level clouds. The instrument for measuring cloud height is called a ceilometer
7. Sunshine. A Campbell-Stokes sunshine recorder measures hours of sunshine that an area receives in a day. Sunshine is obviously important, primarily since is potentially indicates the amount of heat an area is receiving.
Click on the arrow to view this You Tube video that uses the unique conditions of Australia to explain the elements of weather.
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