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63-534: Lopé National Park has dry weather compared to the rest of Gabon, being located in the rain shadow of the Chaillu Massif. In addition, there is a low band of rainfall along the Ogooué River. As a result, the landscape contains a complex mosaic of dense tropical rainforests and savannas. The boundary (called an ecotone ) between the two habitats has shifted since the last ice age , with the rainforest expanding into

126-402: A change in temperature. The numbers are exactly equal if we consider the gases as ideal . The addition of water molecules, or any other molecules, to a gas, without removal of an equal number of other molecules, will necessarily require a change in temperature, pressure, or total volume; that is, a change in at least one of these three parameters. If temperature and pressure remain constant,

189-433: A much lower scale height and shorter atmospheric lifetime — weeks instead of decades. Without other greenhouse gases, Earth's blackbody temperature , below the freezing point of water, would cause water vapor to be removed from the atmosphere. Water vapor is thus a "slave" to the non-condensible greenhouse gases. Humidity is one of the fundamental abiotic factors that defines any habitat (the tundra, wetlands, and

252-419: A non-condensable phase other than air. A device used to measure humidity of air is called a psychrometer or hygrometer . A humidistat is a humidity-triggered switch, often used to control a humidifier or a dehumidifier . The humidity of an air and water vapor mixture is determined through the use of psychrometric charts if both the dry bulb temperature ( T ) and the wet bulb temperature ( T w ) of

315-568: A parcel of air can vary significantly. For example, a parcel of air near saturation may contain 8 g of water per cubic metre of air at 8 °C (46 °F), and 28 g of water per cubic metre of air at 30 °C (86 °F) Three primary measurements of humidity are widely employed: absolute, relative, and specific. Absolute humidity is expressed as either mass of water vapor per volume of moist air (in grams per cubic meter) or as mass of water vapor per mass of dry air (usually in grams per kilogram). Relative humidity , often expressed as

378-412: A percentage, indicates a present state of absolute humidity relative to a maximum humidity given the same temperature. Specific humidity is the ratio of water vapor mass to total moist air parcel mass. Humidity plays an important role for surface life. For animal life dependent on perspiration (sweating) to regulate internal body temperature, high humidity impairs heat exchange efficiency by reducing

441-520: A relatively high humidity post-rainfall. Outside the monsoon seasons, humidity is high (in comparison to countries further from the Equator), but completely sunny days abound. In cooler places such as Northern Tasmania, Australia, high humidity is experienced all year due to the ocean between mainland Australia and Tasmania. In the summer the hot dry air is absorbed by this ocean and the temperature rarely climbs above 35 °C (95 °F). Humidity affects

504-412: Is affected by winds and by rainfall. The most humid cities on Earth are generally located closer to the equator, near coastal regions. Cities in parts of Asia and Oceania are among the most humid. Bangkok, Ho Chi Minh City , Kuala Lumpur , Hong Kong, Manila , Jakarta , Naha , Singapore, Kaohsiung and Taipei have very high humidity most or all year round because of their proximity to water bodies and

567-434: Is almost independent of the amount of air (nitrogen, oxygen, etc.) that is present. Indeed, a vacuum has approximately the same equilibrium capacity to hold water vapor as the same volume filled with air; both are given by the equilibrium vapor pressure of water at the given temperature. There is a very small difference described under "Enhancement factor" below, which can be neglected in many calculations unless great accuracy

630-435: Is also a key metric used to evaluate when it is appropriate to install flooring over a concrete slab. Specific humidity (or moisture content) is the ratio of the mass of water vapor to the total mass of the air parcel. Specific humidity is approximately equal to the mixing ratio , which is defined as the ratio of the mass of water vapor in an air parcel to the mass of dry air for the same parcel. As temperature decreases,

693-487: Is also measured on a global scale using remotely placed satellites. These satellites are able to detect the concentration of water in the troposphere at altitudes between 4 and 12 km (2.5 and 7.5 mi). Satellites that can measure water vapor have sensors that are sensitive to infrared radiation . Water vapor specifically absorbs and re-radiates radiation in this spectral band. Satellite water vapor imagery plays an important role in monitoring climate conditions (like

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756-543: Is an important metric used in weather forecasts and reports, as it is an indicator of the likelihood of precipitation , dew, or fog. In hot summer weather, a rise in relative humidity increases the apparent temperature to humans (and other animals) by hindering the evaporation of perspiration from the skin. For example, according to the heat index , a relative humidity of 75% at air temperature of 80.0 °F (26.7 °C) would feel like 83.6 ± 1.3 °F (28.7 ± 0.7 °C). Relative humidity

819-404: Is carried by the prevailing onshore breezes towards the drier and hotter inland areas. When encountering elevated landforms , the moist air is driven upslope towards the peak , where it expands, cools, and its moisture condenses and starts to precipitate . If the landforms are tall and wide enough, most of the humidity will be lost to precipitation over the windward side (also known as

882-460: Is defined as the ratio of the partial pressure of water vapor ( p {\displaystyle p} ) in air to the saturation vapor pressure ( p s {\displaystyle p_{s}} ) of water at the same temperature, usually expressed as a percentage: φ = 100 % ⋅ p / p s {\displaystyle \varphi =100\%\cdot p/p_{s}} Relative humidity

945-430: Is inappropriate for computations in chemical engineering, such as drying, where temperature variations might be significant. As a result, absolute humidity in chemical engineering may refer to mass of water vapor per unit mass of dry air, also known as the humidity ratio or mass mixing ratio (see "specific humidity" below), which is better suited for heat and mass balance calculations. Mass of water per unit volume as in

1008-595: Is limited to precipitation that crosses over the Continental Divide . While many locations west of the Divide may receive as much as 1,000 millimetres (40 in) of precipitation per year, some places on the eastern side, notably the cities of Denver and Pueblo, Colorado , typically receive only about 12 to 19 inches. Thus, the Continental Divide acts as a barrier for precipitation. This effect applies only to storms traveling west-to-east. When low pressure systems skirt

1071-523: Is much less forested than its surroundings, making an open landscape that may have been used as a corridor and migration route from the coast to the interior of Africa. The oldest Stone Age tools currently known were discovered at Elarmékora in the central region of the valley, in addition to several other Stone Age archeological sites. In the Neolithic , between 3500 and 2000 years ago, the Bantu people may have used

1134-528: Is required. Absolute humidity is the total mass of water vapor (gas form of water) present in a given volume or mass of air. It does not take temperature into consideration. Absolute humidity in the atmosphere ranges from near zero to roughly 30 g (1.1 oz) per cubic metre when the air is saturated at 30 °C (86 °F). Absolute humidity is the mass of the water vapor ( m H 2 O ) {\displaystyle (m_{{\text{H}}_{2}{\text{O}}})} , divided by

1197-549: Is shown in State B. If the system at State A is isothermally compressed (compressed with no change in system temperature), then the relative humidity of the system increases because the partial pressure of water in the system increases with the volume reduction. This is shown in State C. Above 202.64 kPa, the RH would exceed 100% and water may begin to condense. If the pressure of State A was changed by simply adding more dry air, without changing

1260-450: Is the dry-bulb temperature expressed in degrees Celsius (°C), P {\displaystyle P} is the absolute pressure expressed in millibars, and e w ∗ {\displaystyle e_{w}^{*}} is the equilibrium vapor pressure expressed in millibars. Buck has reported that the maximal relative error is less than 0.20% between −20 and +50 °C (−4 and 122 °F) when this particular form of

1323-554: Is the most abundant of all greenhouse gases . Water vapor, like a green lens that allows green light to pass through it but absorbs red light, is a "selective absorber". Like the other greenhouse gasses, water vapor is transparent to most solar energy. However, it absorbs the infrared energy emitted (radiated) upward by the Earth's surface, which is the reason that humid areas experience very little nocturnal cooling but dry desert regions cool considerably at night. This selective absorption causes

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1386-437: Is the ratio of how much water vapour is in the air to how much water vapour the air could potentially contain at a given temperature. It varies with the temperature of the air: colder air can contain less vapour, and water will tend to condense out of the air more at lower temperatures. So changing the temperature of air can change the relative humidity, even when the absolute humidity remains constant. Chilling air increases

1449-629: The Magnus–Tetens approximation , are more complicated but yield better accuracy. The Arden Buck equation is commonly encountered in the literature regarding this topic: e w ∗ = ( 1.0007 + 3.46 × 10 − 6 P ) × 6.1121 e 17.502 T / ( 240.97 + T ) , {\displaystyle e_{w}^{*}=\left(1.0007+3.46\times 10^{-6}P\right)\times 6.1121\,e^{17.502T/(240.97+T)},} where T {\displaystyle T}

1512-501: The Rocky Mountains and approach from the south, they can generate high precipitation on the eastern side and little or none on the western slope. Further east: Humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation , dew , or fog to be present. Humidity depends on

1575-425: The energy budget and thereby influences temperatures in two major ways. First, water vapor in the atmosphere contains "latent" energy. During transpiration or evaporation, this latent heat is removed from surface liquid, cooling the Earth's surface. This is the biggest non-radiative cooling effect at the surface. It compensates for roughly 70% of the average net radiative warming at the surface. Second, water vapor

1638-443: The leopard , protecting healthy populations of its prey species including the red river hog , African forest buffalo , and cane rat . Other mammal species found in the part include the endangered giant pangolin and tree pangolin , often sharing nests with Microchiroptera bat species. Lopé National Park and its surroundings contain evidence of almost continual human occupation over the last 400,000 years. The Ogooué River Valley

1701-520: The monsoon season. High temperatures combine with the high dew point to create heat index in excess of 65 °C (149 °F). Darwin experiences an extremely humid wet season from December to April. Houston, Miami, San Diego, Osaka, Shanghai, Shenzhen and Tokyo also have an extreme humid period in their summer months. During the South-west and North-east Monsoon seasons (respectively, late May to September and November to March), expect heavy rains and

1764-451: The rainward side) before ever making it past the top. As the air descends the leeward side of the landforms, it is compressed and heated, producing foehn winds that absorb moisture downslope and cast a broad "shadow" of dry climate region behind the mountain crests . This climate typically takes the form of shrub–steppe , xeric shrublands or even deserts . The condition exists because warm moist air rises by orographic lifting to

1827-664: The trade winds is the zone between about 30° N and 30° S, blowing predominantly from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisphere . The westerlies are the prevailing winds in the middle latitudes between 30 and 60 degrees latitude , blowing predominantly from the southwest in the Northern Hemisphere and from the northwest in the Southern Hemisphere. Some of

1890-790: The Cordillera, in the direct lee of specific mountain ranges. This includes much of the Basin and Range Province in the United States and Mexico . The Pacific Coast Ranges create rain shadows near the West Coast: Most rain shadows in the western United States are due to the Sierra Nevada mountains in California and Cascade Mountains , mostly in Oregon and Washington . The Colorado Front Range

1953-424: The amount of water vapor needed to reach saturation also decreases. As the temperature of a parcel of air becomes lower it will eventually reach the point of saturation without adding or losing water mass. The term relative humidity is reserved for systems of water vapor in air. The term relative saturation is used to describe the analogous property for systems consisting of a condensable phase other than water in

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2016-663: The atmosphere is as warm or warmer than the skin during times of high humidity, blood brought to the body surface cannot dissipate heat by conduction to the air. With so much blood going to the external surface of the body, less goes to the active muscles, the brain, and other internal organs. Physical strength declines, and fatigue occurs sooner than it would otherwise. Alertness and mental capacity also may be affected, resulting in heat stroke or hyperthermia . Domesticated plants and animals (e.g. lizards) require regular upkeep of humidity percent when grown in-home and container conditions, for optimal thriving environment. Although humidity

2079-413: The base, including several chalets and a large open air dining room, from which the rainforest is a mere five meters away. The park also hosts CEDAMM Training Centre, a Wildlife Conservation Society -run international conservation education center. Because of global climate change , the dense forest ecosystem is expanding into the savanna ecosystem in the north, leading to the loss of habitat diversity in

2142-448: The chilled mirror method is effective. For process on-line measurements, the most commonly used sensors nowadays are based on capacitance measurements to measure relative humidity, frequently with internal conversions to display absolute humidity as well. These are cheap, simple, generally accurate and relatively robust. All humidity sensors face problems in measuring dust-laden gas, such as exhaust streams from clothes dryers. Humidity

2205-415: The desert are a few examples), and is a determinant of which animals and plants can thrive in a given environment. The human body dissipates heat through perspiration and its evaporation. Heat convection , to the surrounding air, and thermal radiation are the primary modes of heat transport from the body. Under conditions of high humidity, the rate of evaporation of sweat from the skin decreases. Also, if

2268-465: The enhancement factor is normally slightly greater than unity for real systems. The enhancement factor is commonly used to correct the equilibrium vapor pressure of water vapor when empirical relationships, such as those developed by Wexler, Goff, and Gratch, are used to estimate the properties of psychrometric systems. Buck has reported that, at sea level, the vapor pressure of water in saturated moist air amounts to an increase of approximately 0.5% over

2331-443: The equation above is also defined as volumetric humidity . Because of the potential confusion, British Standard BS 1339 suggests avoiding the term "absolute humidity". Units should always be carefully checked. Many humidity charts are given in g/kg or kg/kg, but any mass units may be used. The field concerned with the study of physical and thermodynamic properties of gas–vapor mixtures is named psychrometrics . Relative humidity

2394-575: The equator and often overcast weather. Some places experience extreme humidity during their rainy seasons combined with warmth giving the feel of a lukewarm sauna, such as Kolkata , Chennai and Kochi in India, and Lahore in Pakistan. Sukkur city located on the Indus River in Pakistan has some of the highest and most uncomfortable dew points in the country, frequently exceeding 30 °C (86 °F) in

2457-474: The equilibrium vapor pressure of pure water. Climate control refers to the control of temperature and relative humidity in buildings, vehicles and other enclosed spaces for the purpose of providing for human comfort, health and safety, and of meeting environmental requirements of machines, sensitive materials (for example, historic) and technical processes. While humidity itself is a climate variable, it also affects other climate variables. Environmental humidity

2520-418: The formation of thunderstorms) and in the development of weather forecasts . Humidity depends on water vaporization and condensation, which, in turn, mainly depends on temperature. Therefore, when applying more pressure to a gas saturated with water, all components will initially decrease in volume approximately according to the ideal gas law . However, some of the water will condense until returning to almost

2583-409: The generalized formula is used to estimate the equilibrium vapor pressure of water. There are various devices used to measure and regulate humidity. Calibration standards for the most accurate measurement include the gravimetric hygrometer, chilled mirror hygrometer , and electrolytic hygrometer. The gravimetric method, while the most accurate, is very cumbersome. For fast and very accurate measurement

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2646-450: The greenhouse effect. It raises the surface temperature substantially above its theoretical radiative equilibrium temperature with the sun, and water vapor is the cause of more of this warming than any other greenhouse gas. Unlike most other greenhouse gases, however, water is not merely below its boiling point in all regions of the Earth, but below its freezing point at many altitudes. As a condensible greenhouse gas, it precipitates , with

2709-440: The ideal gas law. On the contrary the saturated volume is the volume a gas mixture would have if humidity was added to it until saturation (or 100% relative humidity). Humid air is less dense than dry air because a molecule of water ( m ≈ 18  Da ) is less massive than either a molecule of nitrogen ( m ≈ 28 ) or a molecule of oxygen ( m ≈ 32 ). About 78% of the molecules in dry air are nitrogen (N 2 ). Another 21% of

2772-414: The measure of relative humidity of the air, although their presence is an indication that a body of air may be close to the dew point. Relative humidity is normally expressed as a percentage; a higher percentage means that the air–water mixture is more humid. At 100% relative humidity, the air is saturated and is at its dew point. In the absence of a foreign body on which droplets or crystals can nucleate ,

2835-456: The mixture are known. These quantities are readily estimated by using a sling psychrometer . There are several empirical formulas that can be used to estimate the equilibrium vapor pressure of water vapor as a function of temperature. The Antoine equation is among the least complex of these, having only three parameters ( A , B , and C ). Other formulas, such as the Goff–Gratch equation and

2898-444: The molecules in dry air are oxygen (O 2 ). The final 1% of dry air is a mixture of other gases. For any gas, at a given temperature and pressure, the number of molecules present in a particular volume is constant. Therefore, when some number N of water molecules (vapor) is introduced into a volume of dry air, the number of air molecules in that volume must decrease by the same number N for the pressure to remain constant without using

2961-463: The mountain. The air descends on the leeward side, but due to the precipitation it has lost much of its moisture. Typically, descending air also gets warmer because of adiabatic compression (as with foehn winds) down the leeward side of the mountain, which increases the amount of moisture that it can absorb and creates an arid region. There are regular patterns of prevailing winds found in bands round Earth's equatorial region. The zone designated

3024-501: The park. As a result, annual controlled burns of the savanna have been conducted in the park to reduce the encroachment of the forest vegetation and to provide the required vegetation for the diet of the forest buffalo. Rain shadow A rain shadow is an area of significantly reduced rainfall behind a mountainous region, on the side facing away from prevailing winds , known as its leeward side. Evaporated moisture from water bodies (such as oceans and large lakes )

3087-417: The rate of moisture evaporation from skin surfaces. This effect can be calculated using a heat index table, or alternatively using a similar humidex . The notion of air "holding" water vapor or being "saturated" by it is often mentioned in connection with the concept of relative humidity. This, however, is misleading—the amount of water vapor that enters (or can enter) a given space at a given temperature

3150-491: The relative humidity can exceed 100%, in which case the air is said to be supersaturated . Introduction of some particles or a surface to a body of air above 100% relative humidity will allow condensation or ice to form on those nuclei, thereby removing some of the vapour and lowering the humidity. In a scientific notion, the relative humidity ( R H {\displaystyle RH} or φ {\displaystyle \varphi } ) of an air-water mixture

3213-440: The relative humidity, and can cause the water vapour to condense (if the relative humidity rises over 100%, the dew point ). Likewise, warming air decreases the relative humidity. Warming some air containing a fog may cause that fog to evaporate, as the droplets are prone to total evaporation due to the heat. Relative humidity only considers the invisible water vapour. Mists, clouds, fogs and aerosols of water do not count towards

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3276-403: The same humidity as before, giving the resulting total volume deviating from what the ideal gas law predicted. Conversely, decreasing temperature would also make some water condense, again making the final volume deviate from predicted by the ideal gas law. Therefore, gas volume may alternatively be expressed as the dry volume, excluding the humidity content. This fraction more accurately follows

3339-502: The saturated vapor pressure of pure water: f W = e w ′ e w ∗ . {\displaystyle f_{W}={\frac {e'_{w}}{e_{w}^{*}}}.} The enhancement factor is equal to unity for ideal gas systems. However, in real systems the interaction effects between gas molecules result in a small increase of the equilibrium vapor pressure of water in air relative to equilibrium vapor pressure of pure water vapor. Therefore,

3402-462: The savanna, although the dry climate has allowed the savanna ecosystem to persist in the north of the park. Because of the complex environment, the national park contains unusually high biodiversity across many taxa. Over 1,550 plant species have been recorded to date, with many regions of the park yet to be explored fully. In a survey of land snails in the park, 74 species were found from 12 different families. The park also provides critical habitat for

3465-667: The strongest westerly winds in the middle latitudes can come in the Roaring Forties of the Southern Hemisphere, between 30 and 50 degrees latitude. Examples of notable rain shadowing include: On the largest scale, the entirety of the North American Interior Plains are shielded from the prevailing Westerlies carrying moist Pacific weather by the North American Cordillera . More pronounced effects are observed, however, in particular valley regions within

3528-458: The temperature and pressure of the system of interest. The same amount of water vapor results in higher relative humidity in cool air than warm air. A related parameter is the dew point . The amount of water vapor needed to achieve saturation increases as the temperature increases. As the temperature of a parcel of air decreases it will eventually reach the saturation point without adding or losing water mass. The amount of water vapor contained within

3591-463: The temperature but also on the absolute pressure of the system of interest. This dependence is demonstrated by considering the air–water system shown below. The system is closed (i.e., no matter enters or leaves the system). If the system at State A is isobarically heated (heating with no change in system pressure), then the relative humidity of the system decreases because the equilibrium vapor pressure of water increases with increasing temperature. This

3654-501: The time of the beginning of iron-working, it appears that the valley was abandoned sometime between 600 and 1200 AD, before being repopulated by the present-day Okanda people in the 14th and 15th centuries. The park contains a small research station, named as Mikongo and run by the Zoological Society London, based in the village known as Mikongo, from which it gets its name. There exists infrastructure to cater for tourists at

3717-419: The top of a mountain range. As atmospheric pressure decreases with increasing altitude, the air has expanded and adiabatically cooled to the point that the air reaches its adiabatic dew point (which is not the same as its constant pressure dew point commonly reported in weather forecasts). At the adiabatic dew point, moisture condenses onto the mountain and it precipitates on the top and windward sides of

3780-432: The valley during the Bantu expansion , leaving behind remains of polished stone axes and pottery. During that time, small villages were constructed on the hilltops with large rubbish pits. Later, when iron-working appeared in the valley around 2000 years ago, the hilltop villages became larger, with nearby iron furnaces, and agriculture began to flourish. Although over 1600 petroglyphs have been discovered dating from around

3843-416: The volume increases, and the dry air molecules that were displaced will initially move out into the additional volume, after which the mixture will eventually become uniform through diffusion. Hence the mass per unit volume of the gas—its density—decreases. Isaac Newton discovered this phenomenon and wrote about it in his book Opticks . The relative humidity of an air–water system is dependent not only on

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3906-468: The volume of the air and water vapor mixture ( V net ) {\displaystyle (V_{\text{net}})} , which can be expressed as: A H = m H 2 O V net . {\displaystyle AH={\frac {m_{{\text{H}}_{2}{\text{O}}}}{V_{\text{net}}}}.} If the volume is not set, the absolute humidity varies with changes in air temperature or pressure. Because of this, it

3969-499: The volume, the relative humidity would not change. Therefore, a change in relative humidity can be explained by a change in system temperature, a change in the volume of the system, or change in both of these system properties. The enhancement factor ( f w ) {\displaystyle (f_{w})} is defined as the ratio of the saturated vapor pressure of water in moist air ( e w ′ ) {\displaystyle (e'_{w})} to

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