Through a deep layer within an air mass, the absolute humidity, like the temperature, usually decreases with height. The relative humidity continuously decreases with height in the troposphere and is close to zero in the stratosphere.At lower pressures, the air can hold less water vapour. Therefore, as the altitude increases, the air becomes less dense and the pressure decreases, which means that the air can hold less water vapour. This results in a decrease in absolute humidity at higher altitudes. Since temperature decreases with altitude, warm, humid air rising to higher altitudes in such storms will encounter colder temperatures, and therefore more water is 'freeze dried' out.” These two factors oppose each other, and the overall change in water vapor in the upper troposphere is a combination of these opposing. Relative humidity changes with a change in the temperature and altitude of a particular region. As the altitude of a place increases, the air gets thin and the moisture holding capacity of the air decreases which results in reduced humidity. Relative humidity changes with a change in the temperature and altitude of a particular region. As the altitude of a place increases, the air gets thin and the moisture holding capacity of the air decreases (low atmospheric pressure) which results in reduced humidity. Because the equatorial regions make their own weather. They are perpetually hot throughout the year as the sun rays almost hit them directly with not many changes on the solstices too. The sun rises abruptly (the shortest twilights are in this region) and the earth starts to heat up. Due to the spherical shape of the Earth, sunlight falls on different parts at different angles. Direct and focused sun rays falls on the equator and hence, the regions here are hotter and warmer. The Polar Regions receive diffused sun rays, which is why the areas there are colder. n equatorial lowlands with an equatorial climate, average annual temperatures are about 88°F (31 °C) during the afternoon and 73°F (23°C) around sunrise. Precipitation (in form of rainfall) is very high, from 100 to 140 inches (2,500 to 3,500 millimeters) each year. Wet equatorial lowlands with an equatorial climate, average annual temperatures are about 88°F (31 °C) during the afternoon and 73°F (23°C) around sunrise. Precipitation (in form of rainfall) is very high, from 100 to 140 inches (2,500 to 3,500 millimeters) each year. At the equator the sun is on average straight above and the energy output there is greater than anywhere else on earth. Hence the evaporation there is greater than on most areas on earth. The result is high humidity there, and in areas down-wind from there.

Absolute humidity is the amount of water vapor in a given volume of air. It is measured in grams of water vapor per cubic meter of air.

The absolute humidity decreases at higher altitudes because the air pressure decreases. The air pressure is the force exerted by the weight of the air above a given point. As the altitude increases, there is less air above the point, so the air pressure decreases.

The amount of water vapor that air can hold is dependent on the air pressure. At lower pressures, the air can hold less water vapor. This is why the absolute humidity decreases at higher altitudes.

The temperatures and humidity remain very high in the equatorial regions because the sun's rays are more direct at the equator. The sun's rays heat the ground, which in turn heats the air. The warm air can hold more water vapor, so the humidity is high.

In addition, the equatorial regions are located near the oceans, which are a major source of moisture. The winds that blow over the oceans carry moisture to the equatorial regions, which further increases the humidity.

Here is a table summarizing the relationship between altitude, air pressure, and absolute humidity:

Dr Murtadha Shukur thank you for your contribution to the discussion

Warm air can possess more water vapor (moisture) than cold air, so with the same amount of absolute/specific humidity, air will have a higher relative humidity if the air is cooler, and a lower relative humidity if the air is warmer. The value of absolute humidity differs with air temperature and pressure changes if the volume is not fixed. It is also affected by the water distribution on the Earth and seasonal changes. As it is the measure of absolute moisture in the air, it relatively remains constant. Now, with the increase in temperature the capacity of the atmosphere to hold the water vapour or moisture increases, thus decreases the relative humidity. Hence, with an increase in the temperature of air, the relative humidity will decrease even if the moisture content remains the same. At higher elevations, atmospheric pressure is lower, and consequently, the vapor pressure of water is also lower. This results in less humidity in the air. Absolute humidity is independent of temperature whereas relative humidity is dependent on temperature. Warmer air can store more water molecules, and when it cools, that warm air loses water vapour through condensation. A higher dew point signifies more moisture in the air, resulting in oppressively humid conditions with the possibility for cloud and precipitation.The absolute humidity changes as air temperature or pressure changes, if the volume is not fixed. So when the relative humidity of the air is high, meaning the air has a high moisture content, the sweat evaporation process slows down. It feels hotter to you. The opposite occurs if the air is very dry. Since temperature decreases with altitude, warm, humid air rising to higher altitudes in such storms will encounter colder temperatures, and therefore more water is 'freeze dried' out.” These two factors oppose each other, and the overall change in water vapor in the upper troposphere is a combination of these opposing. It should be noted that relative humidity decreases linearly with an increase in altitude at an average of 4% per kilometer. As altitude increases, temperature decreases. Various factors are responsible for this, including air pressure and water-vapour content. With every 100 metres, the temperature drops by an average of 0.65°C. Where the air is very dry, such as in an area of high pressure, the air can cool by almost 1°C per 100 metres.The relation between humidity and temperature is inversely proportional. If temperature increases, it will reduce relative humidity; thus, the air will become drier. When the temperature decreases, the air will become wetter; therefore, the relative humidity will increase.

Dear Doctor

"Variations in Absolute Humidity

The actual amount of moisture in the air will vary from one air rental to another, and even within an air mass there will be continuing variations in time and space.

The moisture contents of air masses are basically related to their regions of origin. Air masses originating in continental areas are relatively dry. Those coming from the Atlantic or the Gulf of Mexico are moist, and those from the Pacific are moist or moderately moist. As these maritime air masses invade the continent, land stations will observe abrupt rises in absolute humidity. As any air mass traverses areas different from its source region, gradual changes take place as evaporation, transpiration, condensation, and precipitation add or subtract moisture.

Through a deep layer within an air mass, the absolute humidity, like the temperature, usually decreases with height. There are several reasons for this distribution. First, moisture is added to the atmosphere from the surface and is carried upward by convection and upslope and up valley winds. Second, when air is lifted, the water vapor, as well as the air, expands proportionately so that the moisture in any given volume becomes less and less. Thus, the absolute humidity decreases as the air is lifted. Third, since temperature usually decreases upward, the capacity for air to hold moisture decreases upward. Finally, the precipitation process removes condensed moisture from higher levels in the atmosphere and deposits it at the surface.

The normal pattern of decrease of moisture with altitude may be altered occasionally when horizontal flow at intermediate levels aloft brings in moist air. Such flow is responsible for much of the summer thunderstorm activity over large parts of the West. Extremely low absolute humidity is found in subsiding air aloft. This dry air originates near the top of the troposphere and slowly sinks to lower levels. If it reaches the ground, or is mixed downward, it may produce acutely low humidity near the surface and an abrupt increase in fire danger.

If we consider only a very shallow layer of air near the surface, we find that the vertical variation of absolute humidity with height will change during each 24-hour period as conditions favoring evaporation alternate with conditions favoring condensation. During clear days, moisture usually is added to the air by evaporation from warm surfaces; therefore, the absolute humidity decreases upward.

At night, moisture is usually taken from the air near the surface by condensation on cold surfaces and absorption by cold soil and other substances; thus, the absolute humidity may increase upward through a very shallow layer."

Dr Sundus F Hantoosh thank you for your contribution to the discussion