Humidity - Wikipedia
Climate - Relation between temperature and humidity: Tables that show the effect to the pressure of the atmosphere, can be calculated from the absolute humidity dv glaciers 1,, the porous earth nearly , and the rivers and lakes 4 or 5. During summer the air over the United States transports 16 mm ( inch) of. Humidity is the amount of water vapour present in air. Water vapour, the gaseous state of water, As the temperature of a parcel of air decreases it will eventually reach the saturation point without adding or Specific humidity is the ratio of water vapor mass to total moist air parcel mass. 4 Air density and volume; 5 Effects. Nov 15, Relative humidity is the ratio (expressed as a percentage) of the The dew point is the temperature at which a given sample of air will have a relative seen Monday through Friday on WGN News at 11 a.m., 5 p.m. and 9 p.m.
Darwin, Australia experiences an extremely humid wet season from December to April. Shanghai and Hong Kong 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 Marchexpect heavy rains and a relatively high humidity post-rainfall. Outside the monsoon seasons, humidity is high in comparison to countries North of the Equatorbut 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. United States[ edit ] In the United States the most humid cities, strictly in terms of relative humidityare Forks and Olympia, Washington. In general, dew points are much lower in the Western U. The highest dew points consistently found in the US are found in coastal Florida and Texas.
When comparing Key West and Houstontwo of the most humid cities from those states, coastal Florida seems to have the higher dew points on average.
However, Houston lacks the coastal breeze present in Key West, and, as a much larger city, it suffers from the urban heat island effect. The record was set during the Midwest heat wave disaster which was characterised by a very strong temperature inversion which caused cloudless skies during this in spite of an apparent world record surface-based CAPE set at the same time.
Greenhouse Effect Humidity affects 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. Second, water vapor 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".
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Along with other greenhouse gases, water vapor is transparent to most solar energy, as one can literally see. But 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 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 precipitateswith a much lower scale height and shorter atmospheric lifetime- weeks instead of decades. Without other greenhouse gases, Earth's blackbody temperaturebelow the freezing point of water, would cause water vapor to be removed from the atmosphere. Volume thermodynamics and Density of air 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 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.
Discussion on Humidity
This fraction more accurately follows the ideal gas law. For any gas, at a given temperature and pressure, the number of molecules present in a particular volume is constant — see ideal gas law. So when water molecules vapor are introduced into that volume of dry air, the number of air molecules in the volume must decrease by the same number, if the temperature and pressure remain constant.
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, 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. Heat convectionto the surrounding air, and thermal radiation are the primary modes of heat transport from the body. Cor- relation coefficients between the indoor and outdoor conditions are provided in Table 3. We examined the shape of the but not for RH.Temperature and Relative Humidity
However, examination of the scatter relationships using linear, piecewise linear, and loess plot for AH indicated that linear regression provided regression models.
For both spatial tests, Z-scores indicate the probability of autocorrelation. We found evidence of spatial varia- tion for AH. In sensitivity analyses, we examined the relationship between indoor and outdoor maximum and minimum daily average temperatures.
Forced hot air 6 The correlation Radiator 5 The correlation for RH Window air conditioning 4 Both weather metrics exhibited a a piecewise linear relationship, with the threshold shift- Excluding air conditioners.
When measurements from a central site moni- Outdoor A better under- Apparent Relative Absolute standing of how indoor conditions vary with outdoor Outdoor Temperature temperature humidity humidity conditions would help in estimating the likelihood and magnitude of exposure measurement error. Similarly, the correlations were when outdoor temperatures were warmer.
Nevertheless, stud- during the heating season November—April. How- ies have reported associations between cold weather ever, for AH, the magnitude remained strong and was and increased morbidity and mortality.
Given the high similar to the variability observed in the non-heating degree of measurement error, the reason for these sig- season June—September, Figure 4. AH than for lower indoor temperature. Individual mea- Nguyen et al. We instructed occupants AH as an exposure measure. For example, win- other weather measures. Systematic variation in the relation- likely all contribute to this variability.
In homes with accessible tionships Rhomberg et al. Our results suggest thermostats, thermal control and air conditioning use that systematic variation is of concern for temperature, might increase with higher household wealth.
Humidi- apparent temperature, and RH. Top whisker, maximum; bottom whisker, minimum There was spatial variability in the correlation vide the major source of moisture and lead to local between indoor and outdoor AH. Correla- surprising, since in the northeast United States, excur- tions weakened with increasing distance from the Bos- sions of warm, moist air from the Gulf of Mexico pro- ton airport.
However, the decline with distance was Nguyen et al. Loss of salt and water in sweat results in hemoconcentration Keat- inge, This places strain on the cardiovascular and respiratory systems, and combined with increased 0. Absolute humidity is considered to be the most 0. Results are adjusted for dry air is also insufficient because evaporative water air conditioning type loss causes cooling of the lungs Giesbrecht, The observed and water loss in the larger airways Larsson et al.
In fact, increasing the water vapor content in reduces indoor AH levels independent of temperature inspired gas has the same biophysical consequences as Bernstein et al.
Cooling of the upper air- Exposure to cold remove airway contaminants before they can be increases plasma concentrations of norepinephrine and absorbed in the respiratory mucosa Castellani et al. Vasoconstriction limits The elderly are especially vulnerable to cold, dry air heat loss by redistributing blood to the core and causes Anderson and Bell, ; Hajat et al.
Hemo- an increase in cardiac output that supports higher met- concentration resulting from peripheral vasoconstric- abolic production Castellani et al. Cold tion in response to cold weather makes blood more extremities and the lowering of core body temperature prone to clotting. Among the elderly, who often have can induce short-term increases in heart rate and blood roughened arteries by atheroma, this process increases pressure and promote increased blood viscosity Col- the likelihood of thrombus formation.
The loss of salt lins,hemoconcentration, and arterial thrombo- and water in sweat in response to hot temperatures sis that could lead to triggering of acute cardiac events. Overexertion in a cold environment e. Debilitation and immunological senescence nary thrombosis Medina-Ramon and Schwartz, among older persons increase susceptibility to infec- Leukocyte, granulocyte Castellani aran et al.
These results apply to in housing standards. For example, the Nordic coun- residential indoor exposure and may not apply to tries of Sweden, Norway and Finland have very high indoor exposure experienced in settings such as work home energy efficiency standards that aid in adapting environments, office buildings, and nursing homes.
Examination of these relationships in other geo- Healy, This study Shoji et al.