41
votes
Why would it be drier indoors during the winter vs the summer?
The only physics you need to know is that if the temperature is higher the air† can hold more water vapour (the gaseous phase of water). Cool molecules don't have enough energy to free themselves from ...
- 10.9k
28
votes
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At what humidity does it start to rain?
Short answer: humidity is not a proxy for rain starting and no, it does not start raining automatically when 100% humidity is reached (haze or clouds can form though). The onset of rain is dependent ...
- 14k
16
votes
Why does warm air "hold" more moisture?
Saying that warm air "holds" more moisture is technically incorrect, but is a common colloquialism. Let's break it down to the technicalities.
Let's consider a glass of water with a vacuum (no air) ...
- 8,639
15
votes
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Why (actually) is the night sky so bright in the city? How far up is that happening?
What's actually happening is scattering of light, both off of aerosol particles and nitrogen and oxygen molecules.
For a review of quantitative models of light pollution as a function of distance ...
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14
votes
Why would it be drier indoors during the winter vs the summer?
Because cooling air tends to take out moisture, while heating air doesn't change the actual moisture levels.
When air gets colder, it can't "hold" as much water vapor (lower saturation vapor ...
- 8,612
11
votes
What does the notation "kg kg-1" for units mean for specific humidity
Yes, the unit is kilogram per kilogram, but it means kilogram of water (moisture) per kilogram of air.
- 23.2k
11
votes
Why would it be drier indoors during the winter vs the summer?
A psychrometric chart is very useful for those kind of calculations.
There is a lot of information and the chart looks overwhelming at first. You can click on the charts to see a larger version.
35°...
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11
votes
Is "humidity" the quantifiable metric for mugginess?
Relative humidity is just about the most over-used, relatively useless measure of moisture there is. It's just how full the air is, based upon what it can hold, in moisture. Warm air holds more ...
- 8,612
10
votes
How do the pros measure humidity?
The WMO report Instruments and Methods of Observation has a chapter on Measurement of humidity and a separate chapter on Measurement of upper-air pressure, temperature, humidity. The first deals with ...
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9
votes
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How to calculate relative humidity from temperature, dew point, and pressure?
You can refer to this question for more detail on the origin of this formula (based on the Magnus approximation), but if you do some algebra to the expression there for dew point ($TD$) as function of ...
- 17.3k
8
votes
Why do anticyclones bring clear skies in summertime?
Why anticyclones are also called areas of high pressure
Let's call anticyclones areas of high pressure.
Areas of high pressure (anticyclones), pull air towards the earth's surface. The increase in ...
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8
votes
Why does warm air "hold" more moisture?
The water molecule is just another molecule in the atmosphere - except that it's triatomic, whereas 99.97% of the dry atmosphere is monatomic (Argon) and diatomic (Oxygen and Nitrogen). It's also ...
- 151
8
votes
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Relative Humidity approximation from Dew Point and Temperature
The equation for relative humidity is $$RH=100\times \frac{e}{e_s(T)}=100\times \frac{e_s(T_d)}{e_s(T)} \tag{1}$$
Where $T_d$ is the dewpoint temperature and $T$ is the temperature, $e$ is the water ...
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7
votes
Accepted
How to calculate specific humidity with relative humidity, temperature, and pressure
It looks like your program is using an approximation based on
$q \approx w = w_s*RH$ with an approximation of Clausius-Clapeyron to find $w_s$. Looking at a few values of RH,T and P, your ...
- 14k
7
votes
What the humidity metric is hiding?
Weather services rarely state the absolute humidity because it is not easy to determine. Instead, they state the relative humidity.
Absolute humidity is the mass of water vapor divided by the mass ...
- 23.2k
6
votes
Accepted
Why doesn't it snow even when it is below freezing?
Farrenthorpe is right, a little surfing the net for snow distribution would clarify the picture for you. However, I think you are referring to certain times when it rains further north and snows ...
- 14.1k
6
votes
Why does warm air "hold" more moisture?
What is the deep physics or chemistry reason this happens?
In one word, entropy.
In a thousand words (i.e., a picture),
Source: Wikipedia article on Phase Diagram
The above is a phase diagram of ...
- 22.6k
6
votes
How is relative humidity determined from a wet and dry bulb readings?
Edit: 1 May 2021
The following procedure uses the less accurate method from page 455 onward from the scanned sections of the book pictured below, from the original answer.
The procedure is a ...
- 23.2k
6
votes
How do the pros measure humidity?
We use something like an Onset HOBO electronic sensor. They've got logging (and in some cases, networking) built in. They'll typically log both temperature and relative humidity at regular intervals ...
- 4,090
5
votes
What does the notation "kg kg-1" for units mean for specific humidity
The basic idea is that by mentioning $\mathrm{kg}\, \mathrm{kg}^{-1}$ you make it clear that you measure the weight. You can think of it as
$$ 0.01\, \mathrm{kg}\, \mathrm{kg}^{-1} = 1\, \mathrm{wt.}\...
- 1,158
5
votes
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Is it hotter in different places with the same air temperature?
A temperature is a temperature but the effect of that temperature is not always the same. Some things that add to our perception include sun intensity, wind, humidity, and simply what we are used to. ...
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5
votes
Is it hotter in different places with the same air temperature?
While perceptions about the climate can have an effect on how we react to our environment, Guangdong and Minnesota are fundamentally different climates altogether. Using the Koppen-Geiger climate ...
- 574
5
votes
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How to predict when contrails are likely to form over a specific location using public data?
As described here, condensation of cloud particles (i.e., contrail formation) will occur if the mixing between hot and moist exhaust from an aircraft engine and ambient environmental air results in ...
- 1,104
5
votes
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What is the difference between surface specific humidity and surface relative humidity?
Let's put it a different way:
Specific humidity is how much actual water (vapor) is in the air.
More warmth tends to mean more evaporation.
Warming air also raises the limit of how much water it can ...
- 8,612
5
votes
Is "humidity" the quantifiable metric for mugginess?
There are a number of things going on here.
One is microclimate. The data for Houston most likely comes from Houston Intercontinental Airport (IAH), which is 70 miles from the Gulf Coast. Travel ten ...
- 22.6k
5
votes
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How to convert specific humidity ERA5 in kg/kg to g/kg or mm/day?
The specific humidity of ERA5 data is kg/kg, but some articles work with this variable in g/kg. How can I convert this?
Conversion from kg/kg to g/kg is as simple as multiplying by 1000.
Or to ...
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4
votes
Accepted
Does usual city pollution have effects on relative humidity?
By way of reference, "humidity depends on water vaporization and condensation, which, in turn, mainly depends on temperature".
From the information you have supplied in your comments. There are ...
- 23.2k
4
votes
Accepted
Why does relative humidity seem to correlate with high temperature (at least where I live)?
In coastal New Jersey, relative humidity is maximal in the early fall when the ocean temperature is warmest, and minimal in early spring when the ocean is coldest. However, the monthly variation is ...
- 5,922
4
votes
Accepted
How does humidity vary with height in the Earth's atmosphere?
Humidity strongly varies as a function of time and space, which is why standard atmospheres like CIRA may choose to omit it at all. It simply doesn't make sense to include an “average” humidity ...
- 11.4k
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