What cloud conditions might be like? Cloudiness and limited visibility as the main factors determining the complexity of meteorological conditions
From the surface of the Earth, all clouds appear to be at approximately the same height. However, there can be huge distances between them, equal to several kilometers. But what are the highest and lowest of them? This post has all the information you need to become a cloud expert!
10. Stratus clouds (average height - 300-450 m)
Wikipedia information: Stratus clouds are low-level clouds characterized by horizontal layering with a uniform layer, in contrast to cumuliform clouds, which are formed by rising warm currents.
More specifically, the term "stratus" is used to describe flat, misty clouds at the bottom, ranging in color from dark gray to almost white.
9. Cumulus clouds (average height - 450-2000 m)
Wikipedia information: "Cumulus" is Latin for "heap, heap." Cumulus clouds are often described as "plump", "cotton-like" or "fluffy" in appearance and have a flat base.
As low level clouds, they are usually less than 1000 meters in height unless they are a more vertical form of cumulus cloud. Cumulus clouds can appear alone, in lines, or in clusters.
8. Stratocumulus clouds (average height - 450-2000 m)
Wikipedia information: Stratocumulus clouds are a type of cloud characterized by large, dark, round masses, usually in the form of groups, lines or waves, the individual elements of which are larger than those of altocumulus clouds, forming at a lower altitude, usually below 2400 meters .
Weak convective air currents create shallow layers of clouds due to the drier, still air above them, preventing their further vertical development.
7. Cumulonimbus clouds (average height - 450-2000 m)
Wikipedia information: Cumulonimbus clouds are dense, towering vertical clouds associated with thunderstorms and atmospheric instability, formed from water vapor carried by powerful updrafts.
Cumulonimbus clouds can form alone, in clusters, or as a squall along a cold front. These clouds are capable of producing lightning and other dangerous severe weather such as tornadoes.
6. Nimbostratus clouds (average height - 900-3000 m)
Wikipedia information: Nimbostratus clouds usually produce precipitation over a large area. They have a diffuse base, usually located somewhere near the surface at the lower levels and at an altitude of about 3000 meters at the middle levels.
Although nimbostratus clouds are usually dark in color at the base, they are often illuminated from within when viewed from the Earth's surface.
5. Altostratus clouds (average height - 2000-7000 m)
Wikipedia information: Altostratus clouds are a type of mid-level cloud belonging to the stratiform physical category, which is characterized by a generally uniform layer whose color varies from gray to bluish-green.
They are lighter than nimbostratus clouds and darker than tall cirrostratus clouds. The Sun can be seen through thin altostratus clouds, but thicker clouds may have a denser, opaque structure.
4. Altocumulus clouds (average height - 2000-7000 m)
Wikipedia information: Altocumulus clouds are a type of mid-level cloud that belongs primarily to the stratocumulus physical category, characterized by spherical masses or ridges in layers or sheets, the individual elements of which are larger and darker than those of cirrocumulus clouds, and smaller. than that of stratocumulus clouds.
However, if the layers become flocculent due to increased instability of the air mass, then altocumulus clouds become more cumuliform in structure.
3. Cirrus clouds (average height - 5000-13,500 m)
Wikipedia information: Cirrus clouds are a type of atmospheric cloud typically characterized by thin, thread-like filaments.
Cloud filaments sometimes form into tufts of characteristic shapes known collectively as “mare’s tails.” Cirrus clouds are usually white or light gray in color.
2. Cirrostratus clouds (average level - 5000-13,500 m)
Wikipedia information: Cirrostratus clouds are a type of thin, whitish stratus clouds composed of ice crystals. They are difficult to detect and are capable of forming a halo when they take the form of a thin cirrostratus cloud.
1. Cirrocumulus clouds (average height - 5000-13,500 m)
Wikipedia information: Cirrocumulus clouds are one of the three main types of upper-level tropospheric clouds (the other two are cirrus and cirrostratus clouds). Like lower-level cumulus clouds, cirrocumulus clouds signify convection.
Unlike other tall cirrus and cirrostratus, cirrocumulus consists of a small number of transparent water droplets, although they are in a supercooled state.
At a certain height above the earth's surface and consist of droplets of water or ice crystals, or both. All the variety of clouds can be reduced to several types. The currently generally accepted international classification of clouds is based on two characteristics: appearance and the height of their lower boundary.
Based on their appearance, clouds are divided into three classes: separate, unconnected cloud masses, layers with an inhomogeneous surface, and layers in the form of a homogeneous veil. All these forms can be found at different heights, differing in density and size of external elements (lambs, swellings, shafts, ripples, etc.)
According to the height of the lower base above the earth's surface, clouds are divided into 4 tiers: upper (Ci Cc Cs - height more than 6 km), middle (Ac As - height from 2 to 6 km), lower (Sc St Ns - height less than 2 km), vertical development (Cu Cb - can belong to different tiers, and for the most powerful cumulonimbus clouds (Cb) the base is located on the lower tier, and the top can reach the upper).
Cloud cover largely determines the amount of solar radiation reaching the Earth's surface and is a source of precipitation, thus influencing the formation of weather and climate.
The amount of clouds in Russia is distributed rather unevenly. The cloudiest areas are areas subject to active cyclonic activity, characterized by developed advection of moist air masses. These include the north-west of the European part of Russia, the coast of Kamchatka, Sakhalin, the Kuril and Commander Islands. The average annual amount of total cloud cover in these areas is 7 points. A significant part of Eastern Siberia is characterized by a lower average annual cloud amount - from 5 to 6 points. This relatively cloudy area of the Asian part of Russia is within the sphere of action of the Asian anticyclone.
The distribution of the average annual amount of low cloud cover generally follows the distribution of total cloud cover. The largest number of low-level clouds also occurs in the north-west of the European part of Russia. Here they are predominant (only 1-2 points less than the amount of general cloudiness). The minimum amount of low-level clouds is observed in Eastern Siberia, especially in (no more than 2 points), which is characteristic of the continental nature of the climate of these areas.
The annual variation in the amount of both total and lower clouds in the European part of Russia is characterized by minimum values in summer and maximum values in late autumn and winter, when the influence of the Atlantic is especially pronounced. The exact opposite annual variation in the amount of total and lower cloudiness is observed in the Far East, and. Here, the greatest number of clouds occurs in July, when the summer monsoon is in effect, bringing large amounts of water vapor from the ocean. The minimum cloudiness is observed in January during the period of greatest development of the winter monsoon, with which dry, cooled continental air from the mainland enters these areas.
The daily variation of the total amount of clouds throughout Russia is characterized by the following features:
1) its amplitude in most of the territory does not exceed 1-2 points (with the exception of the central regions of the European part of Russia, where it increases to 3 points);
2) the amount of clouds during the day is greater than at night, while in January the maximum occurs in the morning hours; in the central months of spring and autumn, the diurnal cycle is smoothed, and the maximum can shift to different hours of the day; in April the diurnal cycle is closer to the summer type, and in October - to the winter type;
3) the diurnal variation of lower cloudiness practically repeats the diurnal variation of total cloudiness.
The distribution of cloud shapes is characterized by relative constancy in time and space. Almost throughout the entire territory of Russia, among the clouds of the upper tier, Ci of the middle tier – Ac of the lower tier – Sc and Ns predominate
In the annual course in the summer, a predominance of cumulus (Cu) and stratocumulus (Sc) clouds is noted, while the frequency of occurrence of stratus (St) and nimbostratus (Ns), which are frontal, is small, since in summer conditions for active cyclonic activity. The winter, spring and autumn periods in most of Russia are characterized by an increase in the frequency of altostratus (As), altocumulus (Ac) and stratocumulus (Sc) clouds, while in the European part of Russia there is a slight increase in the frequency of stratus and stratus clouds. -cumulus clouds (St).
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According to the international classification, there are 10 main types of clouds of different tiers.
> UPPER LEVEL CLOUDS(h>6km) Spindrift clouds(Cirrus, Ci) are individual clouds of a fibrous structure and a whitish hue. Sometimes they have a very regular structure in the form of parallel threads or stripes, sometimes on the contrary, their fibers are tangled and scattered across the sky in separate spots. Cirrus clouds are transparent because they consist of tiny ice crystals. Often the appearance of such clouds heralds a change in the weather. From satellites, cirrus clouds are sometimes difficult to see.
Cirrocumulus clouds(Cirrocumulus, Cc) - a layer of clouds, thin and translucent, like cirrus, but consisting of individual flakes or small balls, and sometimes as if from parallel waves. These clouds usually form, figuratively speaking, a “cumulus” sky. They often appear along with cirrus clouds. Sometimes visible before storms.
Cirrostratus clouds(Cirrostratus, Cs) - a thin, translucent whitish or milky cover, through which the disk of the Sun or Moon is clearly visible. This cover can be uniform, like a layer of fog, or fibrous. On cirrostratus clouds, a characteristic optical phenomenon is observed - a halo (light circles around the Moon or Sun, false Sun, etc.). Like cirrus, cirrostratus clouds often indicate the approach of severe weather.
> MIDDLE LEVEL CLOUDS(h=2-6 km)
They differ from similar lower-level cloud forms in their high altitude, lower density, and greater likelihood of having an ice phase. Altocumulus clouds(Altocumulus, Ac) - a layer of white or gray clouds consisting of ridges or individual “blocks”, between which the sky is usually visible. The ridges and “blocks” that form the “feathery” sky are relatively thin and are arranged in regular rows or in a checkerboard pattern, less often - in disorder. "Cirrus" skies are usually a sign of pretty bad weather.
Altostratus clouds(Altostratus, As) - a thin, less often dense veil of a grayish or bluish tint, in places heterogeneous or even fibrous in the form of white or gray shreds all over the sky. The Sun or Moon shines through it in the form of light spots, sometimes quite faint. These clouds are a sure sign of light rain.
> LOWER CLOUDS(h According to many scientists, nimbostratus clouds are illogically assigned to the lower tier, since only their bases are located in this tier, and the tops reach a height of several kilometers (middle tier cloud levels). These heights are more typical for clouds of vertical development, and therefore, some scientists classify them as middle-tier clouds.
Stratocumulus clouds(Stratocumulus, Sc) - a cloud layer consisting of ridges, shafts or individual elements thereof, large and dense, gray in color. There are almost always darker areas.
The word “cumulus” (from the Latin “heap”, “heap”) means a crowded, piled-up cloud. These clouds rarely bring rain, only sometimes they turn into nimbostratus clouds, from which rain or snow falls.
Stratus clouds(Stratus, St) - a rather homogeneous layer of low gray clouds, devoid of regular structure, very similar to fog that has risen a hundred meters over the ground. Stratus clouds cover large areas and look like torn rags. In winter, these clouds often remain throughout the day; precipitation usually does not fall on the ground; sometimes there is drizzle. In summer they quickly dissipate, after which good weather sets in.
Nimbostratus clouds(Nimbostratus, Ns, Frnb) are dark gray clouds, sometimes threatening in appearance. Often, low dark fragments of broken rain clouds appear below their layer - typical harbingers of rain or snowfall.
> VERTICAL CLOUDS
Cumulus clouds (Cumulus, Cu)- dense, sharply defined, with a flat, relatively dark base and a dome-shaped white, as if swirling, top, reminiscent of cauliflower. They begin in the form of small white fragments, but soon they form a horizontal base, and the cloud begins to rise imperceptibly. With little humidity and weak vertical ascent of air masses, cumulus clouds foretell clear weather. Otherwise, they accumulate throughout the day and can cause a thunderstorm.
Cumulonimbus (Cb)- powerful cloud masses with strong vertical development (up to a height of 14 kilometers), giving heavy rainfall with thunderstorm phenomena. They develop from cumulus clouds, differing from them in the upper part, consisting of ice crystals. These clouds are associated with squally winds, heavy precipitation, thunderstorms, and hail. The lifespan of these clouds is short - up to four hours. The base of the clouds is dark in color, and the white top goes far above. In the warm season, the peak can reach the tropopause, and in the cold season, when convection is suppressed, the clouds are flatter. Usually clouds do not form a continuous cover. As a cold front passes, cumulonimbus clouds can form a swell. The sun does not shine through the cumulonimbus clouds. Cumulonimbus clouds are formed when the air mass is unstable, when active upward movement of air occurs. These clouds also often form on a cold front when cold air hits a warm surface.
Each genus of clouds, in turn, is divided into species according to the characteristics of their shape and internal structure, for example, fibratus (fibrous), uncinus (claw-shaped), spissatus (dense), castellanus (tower-shaped), floccus (flaky), stratiformis (stratified). ), nebulosus (foggy), lenticularis (lenticular), fractus (torn), humulus (flat), mediocris (medium), congestus (powerful), calvus (bald), capillatus (hairy). Types of clouds, further, have varieties, for example, vertebratus (ridge-shaped), undulatus (wavy), translucidus (translucent), opacus (non-translucent), etc. Further, additional features of clouds are distinguished, such as incus (anvil), mamma (snake-shaped) , vigra (fall stripes), tuba (trunk), etc. And finally, evolutionary features indicating the origin of clouds are noted, for example, Cirrocumulogenitus, Altostratogenitus, etc.
When observing cloudiness, it is important to determine by eye the degree of sky coverage on a ten-point scale. Clear sky - 0 points. It's clear, there are no clouds in the sky. If the sky is covered with clouds no more than 3 points, partly cloudy. Partly cloudy 4 points. This means that clouds cover half the sky, but at times their amount decreases to "clear". When the sky is half covered, cloudiness is 5 points. If they say “sky with gaps,” they mean that the cloudiness is at least 5, but not more than 9 points. Cloudy - the sky is completely covered with clouds of a single blue sky. Cloud cover 10 points.
When landing an aircraft, to assess visibility, the presence or absence of clouds, their shape, the height of the lower boundary, the structural features of the lower boundary of low clouds, as well as the ratio of oblique and horizontal visibility are of great importance.
According to the experimental data of E.I. Gogoleva (5), obtained from a stationary balloon, some patterns were identified in the ratio of horizontal visibility at the earth's surface and oblique visibility under low stratus clouds:
Cloud height no more than 100 m. The oblique visibility range is 25-45% of the horizontal visibility range at the ground. If ground visibility is 1000 - 2000 m, ground objects are detected from a height of 50 m in 40% of cases, and if ground visibility is more than 2000 m - already in 100% of cases.
When the height of the cloud base is less than 100 m the oblique visibility range can sometimes be less than 1000 m even when the horizontal visibility of the ground is 2 - 3 km.
Height of the lower boundary of clouds 100 - 200 m. The oblique visibility range when leaving the clouds is 40 - 70% of the horizontal visibility range near the ground. As the clouds increase, the range of oblique visibility increases. At a height of 100 - 150 m it is 40 - 50% of horizontal visibility at the ground, and at a height of 150 - 200 m - from 60 to 70%.
The height of the cloud base is more than 200 m. In this case, oblique visibility in the subcloud layer is close to horizontal visibility near the ground.
The influence of low clouds on flights is due not only to its location at a low altitude, but also to the complex structure of the lower cloud boundary.
The main forms of lower clouds are stratus (St) and stratocumulus (Sc). Despite their external differences, they are very similar in terms of formation conditions and microstructure. Varieties of St are ruptured-stratus (St fr) and ruptured-nimbus (Frnb) clouds, usually observed in zones of frontal precipitation and prefrontal pressure drop.
The lower boundary of St and Sc is not a sharply defined surface, but represents a certain layer of gradual thickening along the height of the cloud and deterioration of visibility, similar to the transition from haze to dense fog. This structure of the lower edge is explained, first of all, by the heterogeneous structure of low stratus clouds. In their lowest part, these clouds usually consist of very small droplets; with height, the number and size of droplets increase. In this regard, the concept of “lower limit” of cloudiness is to a certain extent arbitrary. The thickness of the transition layer of the cloud base depends on a number of factors, primarily turbulence. In general, it is greater in stratus clouds than in stratocumulus clouds, the lower boundary of which is more clearly expressed (6, 9, 11).
Studies carried out in the Central Administrative District (12, 13) showed that the lower cloud base is a surface that quickly changes its shape, both in time and in space. During the research, comparisons were made of simultaneous measurements of cloud heights at two points located at a distance of 500 m. The comparison showed that fluctuations in the lower boundary of clouds with a height of 100 m and below in 67% of cases do not exceed 0.1 of their height, in 27% of cases the changes reach 0.3 and only 6% of cases are half their height. It was noted that changes in the height of the lower boundary of clouds over a long distance and in a short period of time can be very different.
The level conventionally accepted as the height of the lower boundary of the clouds will be somewhat different when measured in different ways.
Observations from an airplane usually yield lower cloud heights than those from balloon and instrumental observations. The greatest differences occur in the cases of St or St fr with weak surface winds and with small vertical temperature gradients in the subcloud layer, when poor visibility is observed at the Earth's surface due to haze or precipitation. At Sc, as well as with good visibility near the earth's surface, the observations of pilots almost do not diverge from the data of balloon and instrumental observations.
In general, the fluctuation in the height of the lower boundary of the clouds at a given point consists of systematic, periodic and random changes. Systematic changes are determined by the general trend of altitude changes associated with the gradual restructuring of the humidity field of the lower layer of the atmosphere. They are caused by synoptic processes or diurnal cycles.
Periodic changes are of a wave nature and are determined by the nature of the field of air currents at low altitudes. Random changes are disordered fluctuations of a fluctuation nature, caused primarily by turbulence. All of these types of oscillations can occur simultaneously and cause significant temporal and spatial variability in the height of the cloud base.
To analyze changes in the height of the cloud base, as well as its structure in time and space in the area of the Kemerovo airfield, a number of calculations were carried out.
For the period from 2002 to 2004. There were 1123 cases of cloudiness with a height of 200 m and below. A decrease in cloudiness to a height of 200 m or less was taken as one case. If an increase in cloudiness above 200 m was observed for 1 hour or more, and then it decreased again, then this was considered an independent case. Occasionally, no cloud formations were observed during a single low cloud event. All this was taken into account in the overall count of various combinations of low clouds with other cloud forms.
As a result of the study, it was found that during this three-year period, low clouds were observed: fractus-nimbo (Frnb) combined with nimbostratus (Ns) and cumulonimbus (Cb), stratus (St), stratus (St fr) under stratus clouds. All cases were divided into three groups and the frequency of occurrence over a three-year period was calculated for each group (Table 1).
Table 1.1 - Frequency of various forms of low clouds at Kemerovo airport, in percent
The most frequently observed clouds were Frnb under a total mass of Cb (54%). The formation of clouds Frnb under Ns (24%) and St, St fr under St (22%) occurred to approximately equal extent.
In the annual course, the highest frequency of low clouds was observed in the autumn months - in October (11.8%), November (16.9%), and also in the spring - in April (10.2%).
In May there were only 4 cases with low clouds, in June - 36, which corresponds to the minimum frequency of occurrence in the annual course: 0.2% - in May, 3.2% - in June.
Table 1.2 - Annual variation in the frequency of occurrence of cloud heights of 200 m and below at Kemerovo airport, in percent
If we consider the annual variation of low clouds according to the types we have identified (Table 3), we can conclude that Frnb under the total mass of Cb are observed in all months of the year and have 2 maximums: in March (81 days) and November (119 days) .
Table 1.3 - Annual course of frequency (number of cases) of low clouds of various forms
Cloud shape |
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St, St fr with St |
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Frnb with Ns - were not observed in the period from May to September. In the remaining months of the year, the frequency of these clouds is smooth, with a slight maximum in November (63 days) and a minimum in March (20 days).
For the formation of stratus (St) and stratus (St fr) clouds, the most favorable conditions were in July and August (64 days), which is associated with the presence of dense, high fogs in these months, formed after daytime showers, as well as, associated with the passage of warm fronts.
For all low cloud cases, the total continuous duration, mean and maximum duration of low clouds were calculated for all seasons. The results are presented in Table 4.
The longest continuous duration of low cloudiness is typical for the autumn period (299 hours) and winter (246.5 hours). In spring and summer, the number of cases decreases; the continuous duration of low clouds during these periods is 179 and 188 hours, respectively.
Table 1.4 - Frequency of continuous duration of low cloudiness (from 0 to 200m) for seasons of the year, in percent
Season of the year |
Duration (hours) |
Number of cases |
General cont. (h) |
Avg. cont. |
Max cont (h.min) |
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Low cloudiness in the area of Kemerovo airport can persist from 1 to several hours a day. In most cases, the continuous duration of low clouds varies between about 1 hour and 2 - 3 hours in all seasons, but most often there is a decrease in cloudiness with a duration within 1 hour. The exception is summer, when the greatest frequency occurs for a continuous duration of 2 to 3 hours. The number of cases of low clouds with a continuous duration of 7 to 12 hours is small (4 - 6), but there are slightly more of them in autumn (8).
Over the entire three-year period, one case was identified in each season when low cloudiness persisted for more than 13 hours: in January (17 hours 23 minutes), April (14 hours), August (18 hours), October (13 hours 30 minutes).
The average duration in winter, spring, autumn differs little in value from each other (from 2.4 to 2.8 hours). In summer the average duration is 3.1 hours.
Cloudiness is determined visually using a 10-point system. If the sky is cloudless or there are one or more small clouds occupying less than one tenth of the entire sky, then the cloudiness is considered equal to 0 points. When cloudiness is 10 points, the entire sky is covered with clouds. If 1/10, 2/10, or 3/10 parts of the sky are covered with clouds, then the cloudiness is considered equal to 1, 2, or 3 points, respectively.
Determination of light intensity and background radiation level*
Photometers are used to measure illumination. The deflection of the galvanometer needle determines the illumination in lux. You can use photo exposure meters.
To measure the level of background radiation and radioactive contamination, dosimeters-radiometers (Bella, ECO, IRD-02B1, etc.) are used. Typically, these devices have two operating modes:
1) assessment of background radiation based on the equivalent dose rate of gamma radiation (μSv/h), as well as contamination by gamma radiation of samples of water, soil, food, crop products, livestock, etc.;
* Units of measurement of radioactivity
Radionuclide activity (A)- reduction in the number of radionuclide nuclei over a certain
long time interval:
[A] = 1 Ci = 3.7 · 1010 disp./s = 3.7 · 1010 Bq.
Absorbed radiation dose (D) is the energy of ionizing radiation transferred to a certain mass of the irradiated substance:
[D] = 1 Gy = 1 J/kg = 100 rad.
Equivalent radiation dose (N) equal to the product of the absorbed dose by
average quality factor of ionizing radiation (K), taking into account biological
gical effect of various radiations on biological tissue:
[H] = 1 Sv = 100 rem.
Exposure dose (X) is a measure of the ionizing effect of radiation, united
the value of which is 1 Ku/kg or 1 R:
1 P = 2.58 · 10-4 Ku/kg = 0.88 rad.
Dose rate (exposure, absorbed or equivalent) is the ratio of the dose increment over a certain time interval to the value of this time interval:
1 Sv/s = 100 R/s = 100 rem/s.
2) assessment of the degree of contamination of surfaces and samples of soil, food, etc. with beta-, gamma-emitting radionuclides (particles/min. cm2 or kBq/kg).
The maximum permissible radiation dose is 5 mSv/year.
Determination of the level of radiation safety
The level of radiation safety is determined using the example of using a household dosimeter-radiometer (IRD-02B1):
1. Set the operating mode switch to the “μSv/h” position.
2. Turn on the device by setting the “off-on” switch.
V "on" position. Approximately 60 s after switching on the device is ready
to work.
3. Place the device in the place where the equivalent dose rate is determined gamma radiation. After 25-30 s, the digital display will display a value that corresponds to the dose rate of gamma radiation in a given location, expressed in microsieverts per hour (µSv/h).
4. For a more accurate assessment, it is necessary to take the average of 3-5 consecutive readings.
A reading on the digital display of the device of 0.14 means that the dose rate is 0.14 μSv/h or 14 μR/h (1 Sv = 100 R).
25-30 seconds after the device starts operating, it is necessary to take three consecutive readings and find the average value. The results are presented in the form of a table. 2.
Table 2. Determination of radiation level
Instrument readings |
Average value |
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dose rate |
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Registration of the results of microclimatic observations
Data from all microclimatic observations are recorded in a notebook, and then processed and presented in the form of a table. 3.
Table 3. Results of microclimate processing
observations
Temperature |
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ra air |
Temperature |
Humidity |
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on high, |
ra of air, |
air on |
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height, % |
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