Meteorology p1 - humidity
Summary
TLDRThis video lesson introduces key concepts in meteorology, following a review of energy-related topics. It highlights extreme weather statistics in the U.S., such as the hottest and coldest recorded temperatures and the driest and wettest locations. The video then explains the difference between weather (short-term atmospheric conditions) and climate (long-term trends), with a focus on understanding humidity. Key terms like absolute and relative humidity, dew point, and how to use a sling psychrometer to measure them are introduced. The lesson ends with a brief look at how to calculate dew point and relative humidity using reference charts.
Takeaways
- 🌡️ Meteorology continues from energy topics, with many energy concepts applicable to weather.
- 🔥 Hottest temperature recorded: 134°F in Death Valley, California.
- ❄️ Coldest temperature recorded: -80°F in Prospect Creek, Alaska.
- 🌧️ Wettest location: Hawaii with 460 inches of rain in one month.
- 💨 Windiest location: Mount Washington, New Hampshire, with winds up to 231 mph.
- ⛅ Weather refers to short-term atmospheric conditions, while climate covers long-term conditions over years.
- 💧 Humidity refers to the moisture content in the air, with relative humidity being the percentage of water vapor saturation.
- 📈 As relative humidity increases, the chance of rain also increases due to higher water vapor content.
- 🧊 Dew point is the temperature at which air becomes fully saturated and can no longer hold water vapor, leading to precipitation.
- 🧪 A sling psychrometer is used to measure dew point and relative humidity by comparing the wet and dry bulb temperatures.
Q & A
What is the difference between weather and climate?
-Weather refers to the short-term conditions of the atmosphere, such as changes in temperature, moisture, air pressure, and wind, which can fluctuate from hour to hour or day to day. Climate, on the other hand, is the long-term pattern of weather conditions over several years or decades.
What are some extreme weather records in the United States?
-The hottest recorded temperature is 134°F in Death Valley, California. The coldest is -80°F in Prospect Creek, Alaska. The wettest location is Hawaii, which once received 460 inches of rain in one month. The snowiest location is in California with 390 inches of snow in a month, while Baghdad, California holds the record for the longest dry spell at 767 days without rain. The windiest location is Mount Washington, New Hampshire, with winds reaching 231 mph.
What is absolute humidity?
-Absolute humidity is the actual amount of water vapor in the air. For example, a parcel of air might have 10 grams of water vapor. However, this measurement is not commonly used because it doesn’t give a real sense of current weather conditions.
What is relative humidity, and why is it more useful than absolute humidity?
-Relative humidity is the percentage of saturation of the air, indicating how much water vapor the air is holding compared to the maximum it can hold. For instance, 50% relative humidity means the air is holding half of its capacity. It is more useful because it correlates with how comfortable or humid the air feels.
How is relative humidity related to the chance of rain?
-As relative humidity increases, the chance of precipitation also rises. For example, 90% relative humidity indicates a high chance of rain since the air is nearly saturated with moisture.
What is the dew point?
-The dew point is the temperature at which the air becomes fully saturated with water vapor, meaning it cannot hold any more moisture. If the air temperature drops to this point, condensation occurs, often leading to rain or dew formation.
How can the dew point temperature be measured?
-The dew point temperature can be measured using a sling psychrometer, which consists of a wet bulb and a dry bulb thermometer. By finding the difference in temperatures between the wet and dry bulbs, the dew point can be calculated using a reference chart.
How does a sling psychrometer work?
-A sling psychrometer has two thermometers: one with a wet bulb and one with a dry bulb. The wet bulb is moistened and both are swung around. The difference in temperatures between the two bulbs helps calculate relative humidity and dew point using a reference chart.
How do you calculate the dew point using a sling psychrometer?
-To calculate the dew point, subtract the wet bulb temperature from the dry bulb temperature. Find the dry bulb temperature on a reference chart, then find the temperature difference on the top of the chart. Where these values intersect gives the dew point.
How do you calculate relative humidity using a sling psychrometer?
-To calculate relative humidity, subtract the wet bulb temperature from the dry bulb temperature. Using a reference chart, find the dry bulb temperature on the left and the temperature difference on the top. The intersection of these two values gives the relative humidity.
Outlines
🌡️ Introduction to Meteorology and Extreme U.S. Weather Statistics
The speaker introduces the transition from studying energy to meteorology, explaining how concepts from energy will apply to the new unit. They provide interesting weather statistics from across the United States, including the hottest, coldest, wettest, snowiest, driest, and windiest locations. For example, Death Valley holds the highest recorded temperature (134°F), while Prospect Creek, Alaska, experienced -80°F. The weather extremes highlight the diversity of U.S. climate conditions.
🌦️ Difference Between Weather and Climate
The speaker explains the distinction between weather and climate. Weather refers to short-term atmospheric conditions, such as temperature, moisture, air pressure, and wind, which can change hour by hour or day by day. Climate, on the other hand, refers to long-term atmospheric patterns over years or decades. This section clarifies how weather reflects immediate changes, while climate provides an overarching trend.
💧 Humidity: Absolute vs. Relative
The speaker introduces humidity, defining it as the moisture content in the air. Absolute humidity is the specific amount of water vapor present in a block of air (e.g., 10 grams of water vapor). However, absolute humidity isn't widely used because it doesn't reflect actual weather conditions effectively. Instead, relative humidity is more useful, measuring the percentage of saturation in the air. For example, 50% relative humidity means the air is holding half the water vapor it can hold, while 100% means the air is fully saturated.
🌧️ Relative Humidity and Rain Prediction
Relative humidity is linked to the likelihood of rain. As the percentage of water vapor in the air increases, so does the chance of precipitation. The speaker uses examples like Chicago weather to demonstrate that higher relative humidity, such as 90%, correlates with a higher probability of rain. They also explain the dew point, which is the temperature at which air becomes fully saturated, leading to condensation and rainfall.
🌡️ The Dew Point and Measuring Tools
The dew point is the temperature at which the air is holding as much moisture as possible. When air cools to its dew point, it becomes saturated, and condensation occurs. The speaker introduces the sling psychrometer, a tool used to measure the dew point by comparing temperatures from a wet bulb and a dry bulb. By finding the difference between the two, it’s possible to determine the dew point and relative humidity using a reference chart.
📊 Calculating Dew Point and Relative Humidity
This section describes how to use the sling psychrometer and a reference table to calculate the dew point and relative humidity. The speaker walks through examples, such as determining the dew point with a dry bulb temperature of 12°C and a wet bulb temperature of 5°C. The same method applies to finding relative humidity, using dry bulb and wet bulb differences. The summary concludes by highlighting that these tools are essential for understanding humidity.
📈 Concluding Notes on Humidity and Air Pressure Preview
The speaker summarizes the key points covered so far, emphasizing the relationship between relative humidity, the dew point, and how to use a sling psychrometer to measure these variables. They briefly introduce the next topic, which will explore air pressure in the following lesson, and wrap up the screencast session.
Mindmap
Keywords
💡Weather
💡Climate
💡Humidity
💡Relative Humidity
💡Dew Point
💡Sling Psychrometer
💡Absolute Humidity
💡Air Parcel
💡Precipitation
💡Air Pressure
Highlights
Introduction to meteorology after finishing energy-related concepts.
Weather statistics in the U.S., including hottest in Death Valley (134°F) and coldest in Alaska (−80°F).
Hawaii holds the record for wettest place with 460 inches of rain in one month.
Mount Washington, New Hampshire, holds the record for the highest wind speeds at 231 mph.
Definition of weather as short-term atmospheric conditions that can change from hour to hour or season to season.
Climate is defined as long-term atmospheric conditions over periods like two or ten years.
Introduction to humidity: the moisture content in the air, with a focus on absolute and relative humidity.
Relative humidity is explained as the percentage of air saturation with water vapor, where 100% means the air is fully saturated.
Relative humidity and precipitation: as relative humidity increases, the chance of rainfall also increases.
Introduction to dew point: the temperature at which air is fully saturated and can no longer hold moisture.
Explanation of how the dew point is related to weather phenomena, like dew forming on grass.
Introduction to the sling psychrometer, a device used to measure dew point and relative humidity by comparing wet and dry bulb temperatures.
Example of using a psychrometer to find dew point: subtracting the wet bulb from the dry bulb temperature.
Using the relative humidity and dew point chart with the sling psychrometer to determine weather conditions.
Closing remarks on understanding relative humidity, dew point, and the use of psychrometers in weather analysis.
Transcripts
hello ladies and gentlemen and welcome
back we are going into meteorology now
just finishing up the energy part of
this unit and a lot of the terms and
concepts there and energy are going to
carry over now into meteorology here are
some weather statistics across the
united states that you might want to be
familiar with you not you don't the
commitment to memory but they're
definitely pretty interesting
something's like the hottest in Death
Valley California over a hundred or
about 134 degrees Fahrenheit coldest
prospect Creek a camp in Alaska negative
80 degrees Fahrenheit hey wettest in
hawai 460 inches of rain in one month
actually right now on I think we're a
couple inches down from normal and I
think we get around 10 inches of
rainfall roughly around this time of
year and California has gotten I mean
sorry Hawaii 460 inches of one in one
month pretty amazing snowiest in
California 390 inches of snow for a
month driest in Baghdad California once
again another California place 767 days
without rain and windiest we're looking
at a Mount Washington New Hampshire just
a little north of us with the highest
winds recorded a 231 miles per hour
those are well over hurricane-force
winds and you're looking at winds that
we typically see in tornadoes so there
are definitely in within the United
States many a huge number of extreme
cold as the hottest snow these and
driest and windiest it's actually pretty
amazing okay so what is the difference
between weather and climate we commonly
hear these terms being used and here we
have a little definition for it weather
is our short term conditions of the
atmosphere ok deadly differences in
temperature moisture air pressure and
wind along with a couple of other
variables so you're looking they can
change from hour to hour day to day in
season the season climate on the other
hand is our long term conditions what's
our Comment been like for the past two
years three years or over the past ten
years so weathers our short term climate
is our long term conditions one of the
first weather
variables that we're going to be looking
at is humidity humidity is the moisture
content in the air we can look at
humidity in a couple of different ways
the first way we're going to be looking
at is the absolute humidity absolutely
admitting is the actual amount of water
vapor in the air it's a measured amount
so for example okay the parcel there has
10 grams of water vapor what we can look
at a parcel there is like a block of air
so there's our parcel and this would
have 10 grams of water vapor in it so if
the parcel of air changes possibly the
amount of water vapor in that or the
amount changes we don't really use
absolute humidity too much only because
it doesn't give us a real feel of the
actual weather condition it can be
useful in some situations but it doesn't
really help us more commonly we look at
relative humidity hey relative humidity
is the percentage of saturation of the
air okay so what do we mean okay so
fifty percent humidity means that the
air is holding half of the water it is
capable of holding okay one hundred
percent humidity humidity is when the
air is holding all the water vapor it
can possibly hold or the air is fully
saturated so a hundred percent rather me
the air is fully saturated okay so once
again one hundred percent humidity means
that the air is fully saturated try to
stick that to memory that's not going to
show up in your reference table what is
relative humidity again relative
humidity is the percentage of water
vapor in the air so if we look at this
parcel parcel a as being will say it's
100 grams and you can see that the dark
blue spot right here is our water
suppose we have 50 grams of water in
this parcel that's 100 grams so if we do
the percent which would be 50 grams over
100 grams get
fifty percent I'm parcel be parcel looks
about the same 100 grams but now our
dark blue region has increased its more
well rule say this is about 80 grams of
water so now parcel be we could do the
percentage 80 over 100 grams to get our
eighty percent so parcel B is filled
with more water so when it's filled with
more water the relative humidity goes up
we can also look at relative humidity
and the chance of rain we have two
screencasts screenshots right here and
we can see local weather in Chicago 73
degrees and looking down through you can
see that the some rain appearing same
thing we could look at the hourly think
tuesday 72 degrees for the highs and
lows but we also see rain that is a
correlation between relative humidity
and rain as the relative humidity
increases the chance of precipitation
also increases and that would have a
tendency to make sense as there's more
water vapor in the air we potentially
could have more rainfall an example
would be ninety percent humidity
relative humidity very high chance of
rain
another term we're gonna have to be
familiar with is the dew point the dew
point is the temperature at which air is
holding the maximum amount of water
vapor it can hold so for instance if
maybe the dew point temperature is 12
degrees Celsius and the air temperature
reaches 12 degrees Celsius the air will
now become fully saturated and the air
temperature has reached its dew point it
cannot hold any more water this image
down here in the bottom we often
associate like during the summer we see
dew on the grass what happened this is
at the night during the night the
temperatures dropped making the air more
saturated and the water ended up scanned
ensing on the grass like I said earlier
the dew point temperatures at which air
is fully saturated and can hold no more
moisture we can find that dew point
temperature using what's called a sling
psychrometer the sling psychrometer
looks like this device right here it's
got a little handle and it's got two
thermometers on it it's got a wet bulb
and this one a dry bulb the wet bulb is
like it says who dis little cotton gauze
gets wet and then we take this and we
sling the whole thing around and what
ends up happening is by finding the
differences in the temperature between
the wet bulb and dry bulb we're actually
able to find the dew point temperature
using a chart that's in our reference
table here's a little cartoon so we have
the temperature 53 degrees our dew point
temperature is 51 and this is our parcel
of air right here and notice there
something in the air saying we're almost
there temperature drops it's going down
from 53 to 52 degrees dewpoint
temperature notice it stays the same
we're getting ready and then finally
when the air tent when the temperature
reaches our dew point temperature let's
do it it begins to rain so here as our
air temperature reaches our dew point
temperature relative humidity
humidity is increasing and here it
finally increased so much d I became
saturated and it rain if we open up our
reference table we can find our dew
point and relative humidity chart the
dew point relative humidity chart is
used with the sling psychrometer
remember the sling psychrometer has a
wet bulb and a dry bulb from the
difference between our wet bulb and dry
bulb right here on the top okay
difference means we subtract wet- dry
and using our dry bulb temperature on
the from the sling psychrometer which is
the same as your air temperature we're
able to find our dew point and relative
humidity so an example B what is the dew
point temperature if the dry bulb is 12
degrees celsius and the wet bulb is 5
degrees Celsius well first we go to the
left side and we find our dry bulb
temperature or our air temperature then
what we need to do is we need to find a
difference between our web bulb and our
dry bulb so 12 minus 5 equals 7 so we go
up to the top we find 7 and where the
two numbers meet is our dew point
temperature so here dew point is
negative 5 done pretty easy we can do
the same exact thing to find our
relative humidity
using the sling psychrometer we can also
find the relative humidity we can do the
same exact procedure we did before so we
know we need to know our dry bulb and we
need to know our wet bulb so we go to
the left side look for our dry bulb
temperature of six degrees Celsius then
we need to find the difference between
the wet bulb and dry bulb six minus
three equals three find three on the top
and we're going to move down to where we
both hit and there you go fifty-nine
percent same exact procedure for using
dew point and relative humidity we're
going to stop here for this screencast
we've covered a lot between relative
humidity and using the sling
psychrometer with the relative humidity
dew point charts next time we start
we're going to go into air pressure
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