This glossary is designed to explain, as simply as possible, some of the terms used on these pages.
| Absolute humidity | The weight of water vapour in the air per unit volume of air, usually expressed in g/m3 |
| Absolute barometric pressure | The barometric pressure actually measured at any place. |
| Altitude | The height of a place expressed in metres above sea level at high water spring tide. In reality, the sea level is arbitrary and can vary considerably from one spring tide to the next, so most countries have a fixed point from which altitudes are triangulated. |
| Anemometer | A device to measure wind speed, either by horizontally rotating wind cups or a vertical propellor. |
| Anticyclone | A large weather system characterised by high pressures, generally mild clockwise winds and often clear skies. In summer, they are usually associated with hot weather and, in winter, rather cold night-time temperatures. |
| Average wind speed | The wind speed averaged over, say, 10 minutes. |
| Beaufort number | An arbitrary, non-linear and unscientific scale of 0 to 12 to represent wind speed, based initially on the appearance of the sea. 0 is less than 1 m/s, 1 is 1-2 m/s, 2 is 2-4 m/s, 3 is 4-7 m/s, 4 is 7-10 m/s, 5 is 10-12 m/s, 6 is 12-15 m/s, 7 is 15-18 m/s, 8 is 18-20 m/s, 9 is 20-26 m/s, 10 is 26-30 m/s, 11 is 30-33 m/s and 12 is >33 m/s. (These values may vary considerably from one author to another) |
| Climate | The annual weather cycle averaged over several years. Cyprus enjoys a Mediterranean climate characterised by hot, dry summers and mild, wet winters, with very short transitional spring and autumn seasons. |
| Cloud | The formation of fog at altitudes higher than ground level. There are various types of cloud characterised by their altitude and appearance. |
| Cloud height | The cloud height shown in the graphical data (in feet) is not measured but is a theoretical estimation of the lowest cloud level, based on the conditions on the ground. Note that this is given, even in a cloudless sky. |
| Data logger | Data are uploaded to the computer roughly once per minute, while it is switched on. When the computer is switched off, the data are logged by the weather station itself and then downloaded to the computer when it is switched on. Because this model can record only 175 sets of data, the data cannot be logged so frequently. The night time data are therefore only suitable for studying the general trends and peak responses cannot be considered accurate. |
| Depression | A medium to large weather system, characterised by significantly low pressures in the centre, high anticlockwise winds and often considerable and persistent rain. |
| Dew | When an object or the ground falls in temperature to below that at which the air becomes saturated, the atmospheric humidity condenses on it, forming dew. |
| Dew Point | The highest temperature of an object at which condensation will form on it. |
| Ephemerides | The daily data relating to the sun and the moon for the latitude, longitude and altitude of the observer |
| Fire index | This is an arbitrary scale based on the risk of vegetation catching fire, based on rain history, humidity, temperature and wind. |
| Fog | Fog occurs when the air becomes saturated and nucleation of moisture on particles seriously reduces visibility |
| Full moon | This occurs when the sun fully illuminates the surface of the moon facing the earth. (An eclipse of the moon occurs when the shadow of the earth obscures the full moon.) |
| Gust | A short-term peak of wind. As weather stations sample the data at frequent intervals, and the anemometer must have some inertia, there is never any guarantee that peak gust speeds are measured accurately. However, this lack of accuracy (while the computer is working) is not important. On the other hand, if the computer is not working (night-time), there is a good chance that peak gust strength is missed by the data logger |
| Haze | There are several kinds of haze of different origins, but in this context we are referring to lowered visibility primarily due to humidity levels in excess of about 80% |
| Heat index temperature | The hot weather perceived temperature by humans, based on the real temperature, the wind speed and humidity. This is the temperature that a human would imagine the temperature to be if the humidity were low. |
| Humidity sensor | A device consisting of a special plastic material whose electrical characteristics change according to the amount of humidity in the air. |
| Imperial units | Obsolescent units of measure, rarely used in scientific circles, e.g., degrees Fahrenheit, knots, mph, inches of mercury etc. See Metric units |
| Metric units | Scientific units of
measure, preferred in most countries. These are usually: Temperature: degrees Celsius (°C) Relative humidity: percent (%) Wind speed: metres per second or m/s (m.s-1) or kilometres per hour or km/h (km.h-1) Barometric Pressure: hectopascals (hPa) - this is the same as millibars Rainfall: millimetres (mm) |
| Mist | Mist occurs as water droplets nucleating on cold particles at humidities in the range of 95-99% |
| New moon | The moon is deemed new when it cannot be observed from any place on earth, essentially because the sun is behind it (an eclipse of the sun occurs when the new moon is actually aligned with the sun). |
| Ozone | An allotrope of oxygen. An ozone molecule contains three oxygen atoms, as opposed to two in ordinary oxygen gas. It is highly toxic and dangerous to young children and the elderly. It is common in towns in summer, mainly because weather conditions may promote a reaction, notably because of motor traffic (see volatile organic compounds). Note that ozone in the stratosphere (the "ozone layer", mainly between 12 and 50 km altitude) is essential to life as it filters out harmful UV light. |
| Relative barometric pressure | The measured barometric pressure compensated from the altitude difference down to sea level. |
| Relative humidity | The percentage of humidity in the air, relative to the maximum amount that the air can hold (saturation) at the current temperature. |
| Stevenson screen | Traditionally, a louvred wooden box, painted glossy white, housing temperature and humidity recorders, to protect the latter from heating due to exposure from sunlight. In reality, this is effective only when there is sufficient wind to ensure an air movement through the box. For this reason, some models are equipped with ventilators. |
| Visibility | The visibility is a measure of the distance that one can make out objects, measured in metres or kilometres. Rain, haze, mist and fog are non-exclusive weather-based factors that reduce visibility. Air-borne dust and some kinds of pollution may also reduce visibility (see volatile organic compounds) |
| Volatile organic compounds, VOCs. | These are, as the name implies, volatile chemicals of organic origin. They may be natural or man-made. Their presence usually imparts a blue "heat" haze to the atmosphere, reducing visibility. Natural sources are emanations from mainly aromatic plants, pine trees etc., emitting terpenes and terpenoids. Man-made VOCs are mainly due to unburnt fuel (petrol and diesel) vapours and some other chemicals. VOCs can react with nitrogen oxides from fertilisers, lightning and combustion products (notably vehicle exhausts), in the presence of sunlight, to form ozone, a toxic gas that can inconvenience many people and may be dangerous for young children and the elderly. |
| Weather | Weather is the instantaneous combination of many variables, including temperature etc. |
| Weather Station | A system designed to make measurements of the variables pertaining to weather (temperature, humidity, barometric pressure, wind speed and direction etc.). In this case, we are using a La Crosse WS2300 system, interfaced into a computer with WeatherDisplay software. |
| Wet bulb temperature | The most accurate way of measuring relative or absolute temperature is to use two thermometers, one of which is kept wet by a pure water wick surrounding the bulb. Except at 100% humidity, the wet bulb will always indicate a lower temperature than the dry one. The conversion from the two temperature readings to either humidity is done by either tables or a mathematical formula. |
| Wind chill temperature | The perceived cold weather temperature by humans, based on the real temperature, the wind speed and humidity. This is the temperature that a human would imagine the temperature to be if there were no wind movement. |
| Wind direction sensor | A device that turns like a weather vane and generates an electric signal in phase quadrature, according to the direction. |