Weather lesson 1

Sunshine recorder

A Campbell-Stokes sunshine recorder A sunshine recorder is a device that records the amount of sunshine at a given location. The results provide information about the weather and climate of a geographical area. This information is useful in meteorology, science, agriculture, tourism, and other fields. It has also been called a heliograph. There are two basic types of sunshine recorders. One type uses the sun itself as a times scale for the sunshine readings. The other type uses some form of clock for the time scale.

How are clouds formed

All air contains water, but near the ground it is usually in the form of an invisible gas called water vapor. When warm air rises, it expands and cools. Cool air can't hold as much water vapor as warm air, so some of the vapor condenses onto tiny pieces of dust that are floating in the air and forms a tiny droplet around each dust particle. When billions of these droplets come together they become a visible cloud.

Anemometer

An anemometer is a type of weather instrument that measures wind speed. Anemometers are common at weather stations. A cup anemometer is a type of instrument that uses three or four hemispherical cups mounted on horizontal arms on a vertical rod. The wind pushes the cups and causes the arms to rotate at a rate proportional to the wind speed. A windmill anemometer is a common instrument used at weather stations to obtain the wind speed.

Okta

An okta is a unit of measure used in meteorology to describe how much of the sky is covered in cloud. The word okta means "eighths" and is used because sky conditions are estimated by dividing the sky into eight slices (like a pie) and visually observing how many of those slices' area is covered in cloud. Sky Cover/Cloudiness Scale 0 oktas = clear sky 1-2 oktas = few 3-4 oktas = scattered 5-7 oktas = broken 8 oktas = overcast

Barometer

Atmospheric pressure is measured by barometers. An aneroid barometer, one of the most common types, uses a sealed can of air to detect changes in atmospheric pressure. As the atmospheric pressure goes up, it pushes in on the can, and the can is slightly reduced in volume, moving an indicator needle towards higher pressure. If the atmospheric pressure goes down, the can expands slightly and the needle indicates lower pressure. Some barometers in the past used special graph paper to track changing pressure over time; now, they report electronic signals to a computer, which plots the trends of pressure on computer monitors.

Cirrus clouds

Cirrus clouds are the most common of the high clouds. They are composed of ice and are thin, wispy and curly clouds blown in high winds into long streamers. Cirrus clouds are usually white and predict fair to pleasant weather. By watching the movement of cirrus clouds you can tell from which direction weather is approaching. When you see cirrus clouds, it usually indicates that a change in the weather will occur within 24 hours.

Why do clouds turn gray

Clouds are made up of tiny water droplets or ice crystals, usually a mixture of both. The water and ice scatter all light, making clouds appear white. If the clouds get thick enough or high enough all the light above does not make it through, hence the gray or dark look. Also, if there are lots of other clouds around, their shadow can add to the gray or multicolored gray appearance.

Condensation

Condensation is the change of water from its gaseous form (water vapor) into liquid water. Condensation generally occurs in the atmosphere when warm air rises, cools and looses its capacity to hold water vapor. As a result, excess water vapor condenses to form cloud droplets. The upward motions that generate clouds can be produced by convection in unstable air, convergence associated with cyclones, lifting of air by fronts and lifting over elevated topography such as mountains.

Cumulonimbus

Cumulonimbus clouds are thunderstorm clouds. High winds can flatten the top of the cloud into an anvil-like shape. Cumulonimbus clouds are associated with heavy rain, snow, hail, lightning and even tornadoes. The anvil usually points in the direction the storm is moving.

Cumulus

Cumulus clouds are white, puffy clouds that look like pieces of floating cotton. Cumulus clouds are often called "fair-weather clouds". The base of each cloud is flat and the top of each cloud has rounded towers. When the top of the cumulus clouds resemble the head of a cauliflower, it is called cumulus congestus or towering cumulus. These clouds grow upward and they can develop into giant cumulonimbus clouds, which are thunderstorm clouds.

Dew

Dew is water in the form of droplets that appears on thin, exposed objects in the morning or evening due to condensation. When temperatures are low enough, dew takes the form of ice; this form is called frost. Because dew is related to the temperature of surfaces, in late summer it forms most easily on surfaces that are not warmed by conducted heat from deep ground, such as grass, leaves, railings, car roofs, and bridges.

Drizzle

Drizzle consists of very small droplets of water falling from low level stratus clouds. Size: Drizzle droplets are less than 0.5 mm in diameter - larger than the droplets in clouds, but smaller than raindrops.

Evaporation

Evaporation is the process by which water is converted from its liquid form to its vapor form and thus transferred from land and water masses to the atmosphere. Evaporation from the oceans accounts for 80% of the water delivered as precipitation, with the balance occurring on land, inland waters and plant surfaces.

Sleet

Sleet has no internationally agreed definition but is reported in meteorological observations as "rain and snow mixed". Sleet, which is sometimes known as ice pellets, is basically snow which has begun the melting process before it reaches the ground.

Stratus clouds

Stratus clouds are straight uniform grayish clouds that often cover the entire sky. They resemble fog that doesn't reach the ground. Light mist or drizzle sometimes falls out of these clouds.

Weather

Weather is the day to day hour to hour condition of the atmosphere at particular place at a particular time.

Clouds

A cloud is a large collection of very tiny droplets of water or ice crystals. The droplets are so small and light that they can float in the air.

Climate

Climate is the average weather condition of a region over a period of 20-30 years.

Diamond dust

Diamond dust, sometimes just called ice crystals, consists of extremely small ice crystals, usually formed at low levels at temperatures below -30 °C. The name diamond dust comes from the sparkling effect created when light reflects on the ice crystals in the air.

Meteorologist

Meteorologist is a scientist who studies the atmosphere. They examine its effects on the environment, predict the weather, or investigate climate trends.

Meteorology

Meteorology is the scientific study of the atmosphere that focuses on weather processes and forecasting.

Precipitation

Precipitation is any form of water - liquid or solid - falling from the sky. It includes rain, sleet, snow, hail and drizzle plus a few less common occurrences such as ice pellets, diamond dust and freezing rain.

Rain

Rain is drops of liquid water falling from the sky. In order for the raindrops to become heavy enough to fall, droplets of water in the cloud collide together with other droplets and other particles in the air - like soot and dust - to become larger. Once the drops become too heavy to stay in the cloud, we get rain.

Why are clouds white

Since light travels as waves of different lengths, each color has its very own unique wavelength. Clouds are white because their water droplets or ice crystals are large enough to scatter the light of the seven wavelengths (red, orange, yellow, green, blue, indigo, and violet), which combine to produce white light.

Hygrometer

A hygrometer is an instrument used to measure relative humidity. Humidity is the measure of the amount of moisture in the air. A psychrometer is an example of a hygrometer. A psychrometer uses two thermometers to measure relative humidity; one measures the dry-bulb temperature and the other measures the wet-bulb temperature. (When you come out of your shower in the morning, your skin cools to the wet-bulb temperature and you feel a chill until the water evaporates.) The wet-bulb thermometer contains water in the base that evaporates and absorbs heat which decreases the temperature reading. To determine the relative humidity, the temperatures are taken from the dry-bulb thermometer and the temperature difference between the wet and dry bulb thermometers. From these measurements, a table is used to find the relative humidity at a certain location. A sling psychrometer is a common instrument used by meteorologists to determine the relative humidity. This instrument is swung around while being held.

Rain gauge

A rain gauge is an instrument used to measure the amount of liquid precipitation over a certain length of time. In its simplest sense, a rain gauge is nothing more than a can which collects water which falls from the sky as rain. The depth of the rain can be measured with a ruler. Precipitation is measured in millimeters (mm). Rain gauges are placed in open areas where there are no obstructions. Rain gauges do have limitations. During hurricanes, high winds make liquid measurements in rain gauges impossible. Also, when the temperature approaches freezing (0°C), liquid may freeze around the rain gauge and block the opening. A common type of rain gauge used at weather stations is the heated tipping bucket. This rain gauge melts frozen precipitation around the opening and keeps the precipitation in liquid form when it enters the bucket. As rain enters the funnel of the tipping bucket rain gauge, the rain drips into one of the two buckets that are balanced on a pivot below the funnel. When the bucket tips, it triggers a reed switch which sends data back to the weather station on the amount of precipitation in the bucket. However, the heating element can cause evaporation of small amounts of rain before it gets to the measuring funnel. Also, the tipping bucket can jam or overflow in high-intensity rain like thunderstorms, which can cause errors in the precipitation amount.

Thermometer

A thermometer is an instrument used to measure temperature. Thermometers are used to measure outside and inside temperature, body temperature, oven temperature, and food temperature.

Forecaster

A weather forecaster is a person whose job is to study weather conditions and make reports predicting what the weather will be like for the next few days.

Wind vane

A wind vane, also known as a weather vane, is a tool used to determine the direction the wind is blowing from. These instruments have been in use for centuries, dating from around 50 BCE. They come in many designs, from sleek and professional to ornamentally fun, but they usually follow similar aerodynamic design rules. A number of giant wind vanes exist, and there is a dispute about the largest one in the world.