Definitive Guide to Skew-Ts and Hodographs - Part 6 - Hodograph Basics
Summary
TLDRThis video delves into the construction and interpretation of a hodograph, a visual representation of wind shear in the atmosphere. The instructor explains the concept of wind vectors, highlighting the importance of wind direction and speed. By analyzing raw meteorological data, they demonstrate step-by-step how to plot wind vectors on a polar coordinate grid, ultimately creating a hodograph that illustrates the wind profile. The video provides a practical guide for understanding and visualizing wind shear patterns, laying the foundation for further analysis of storm-related parameters in subsequent videos.
Takeaways
- 📐 A hodograph is a graphical representation of wind shear (change in wind speed and direction with height) in the atmosphere.
- 🌪️ Wind shear can be speed shear (change in wind speed) or directional shear (change in wind direction).
- 📏 A hodograph plots wind vectors using polar coordinates: radial distance for wind speed and angle for wind direction.
- ➡️ Wind direction is measured in degrees, with 0° representing wind from due north and increasing clockwise.
- 💨 Wind vectors are plotted from the origin, with length representing wind speed and angle representing wind direction.
- 🔄 To construct a hodograph, wind vectors are plotted from raw data (wind speed and direction at different heights).
- ⛓️ The tips of the wind vectors are connected to form the hodograph curve.
- 🌀 The shape of the hodograph curve reveals information about wind shear, storm motion, and storm-relative helicity.
- 📊 Hodographs are simpler to interpret than skew-T diagrams for visualizing wind profiles.
- 🔎 Parameters like wind shear, storm motion, and storm-relative helicity can be estimated from the hodograph.
Q & A
What is a hodograph?
-A hodograph is a visual representation of the wind shear in the atmosphere, showing how wind speed and direction change with height.
How is wind direction represented on a hodograph?
-Wind direction is represented by the angles (theta) radiating from the origin of the hodograph, with 0 degrees representing wind from the north, 90 degrees from the east, 180 degrees from the south, and 270 degrees from the west.
How is wind speed represented on a hodograph?
-Wind speed is represented by the distance from the origin, with each concentric ring representing a specific wind speed value (e.g., 10 knots, 20 knots, etc.).
What are polar coordinates, and why are they used in a hodograph?
-Polar coordinates represent a point using an angle (theta) and a radius (r). They are used in a hodograph because wind is a vector quantity with both direction (theta) and magnitude (r, or speed).
How do you plot a wind vector on a hodograph?
-To plot a wind vector on a hodograph, find the angle (theta) corresponding to the wind direction, and then move along that angle from the origin to the distance representing the wind speed (r).
What is the purpose of connecting the tips of the wind vectors on a hodograph?
-Connecting the tips of the wind vectors creates the hodograph curve, which provides a visual representation of the wind shear profile in the atmosphere.
What information can be derived from a hodograph?
-A hodograph can be used to find wind shear between different levels, storm relative helicity, storm motion, and other atmospheric parameters related to wind profiles.
How does a hodograph differ from a skew-T diagram?
-A hodograph focuses solely on wind speed and direction, while a skew-T diagram provides a more comprehensive representation of atmospheric conditions, including temperature, moisture, and stability profiles.
Why is it important to study wind shear in atmospheric analysis?
-Wind shear is crucial in atmospheric analysis because it can impact the development and behavior of severe weather systems, such as thunderstorms and tornadoes, and is a key factor in aviation safety.
What is the advantage of using a hodograph over raw wind data?
-A hodograph provides a visual and intuitive representation of the wind profile, making it easier to identify patterns and analyze wind shear compared to interpreting raw wind data alone.
Outlines
🌀 Introduction to Hodographs
This paragraph introduces hodographs, which are visual representations of wind shear (the changing of wind speed and direction with height) in the atmosphere. The host explains that hodographs are simpler diagrams than skew-T diagrams and only take into account wind direction and speed. He also reviews the concept of wind vectors, which represent the magnitude (speed) and direction of wind.
🔢 Reading Raw Wind Data
The host explains how to read raw wind data, which includes wind direction in degrees (0 degrees is from due north, 90 degrees is from the east, etc.) and wind speed in knots. He demonstrates how to interpret specific data points, such as a wind vector with a direction of 190 degrees and a speed of 6 knots, and how to represent them visually.
📐 Plotting Wind Vectors on a Hodograph
This paragraph walks through the process of plotting wind vectors on a hodograph, which uses polar coordinates (r for wind speed and theta for wind direction). The host explains how to locate specific wind directions on the hodograph and plot the corresponding wind speed from the origin. He plots several wind vectors from the raw data as examples.
🔄 Connecting Wind Vectors to Create a Hodograph
In this paragraph, the host demonstrates how to connect the tips of the plotted wind vectors to create the final hodograph. He explains that the resulting curve represents the wind profile and shear in the atmosphere, and that various quantities like wind shear between layers and storm relative helicity can be derived from the hodograph, which will be covered in the next video.
Mindmap
Keywords
💡Hodograph
💡Wind Shear
💡Vector
💡Polar Coordinates
💡Wind Direction
💡Wind Speed
💡Raw Data
💡Skew-T Diagram
💡Storm Relative Helicity
💡Storm Motion
Highlights
The hodograph is a visual representation of the wind shear, which is the changing of wind speed and direction with height.
The hodograph is a simpler diagram than the skew-T, and it only takes into account wind direction and wind speed.
Winds are represented as vectors, which show the magnitude (speed) and direction.
Wind direction is given in degrees, with 0/360 degrees representing north, 90 degrees representing east, 180 degrees representing south, and 270 degrees representing west.
The hodograph is plotted using polar coordinates, where the spokes represent wind direction (theta) and the rings represent wind speed (r).
The process of plotting a hodograph from raw data, including identifying wind direction and speed at different pressure levels, is demonstrated.
The tips of the wind vectors are connected to create the hodograph curve, which represents the wind profile and shear in the atmosphere.
The hodograph can be used to find various quantities, such as wind shear between different levels and storm relative helicity, which will be discussed in the next video.
The transcript covers the basics of creating a hodograph from raw data and its importance in understanding wind shear and other atmospheric phenomena.
The speaker encourages viewers to watch the previous videos in the series on skew-T diagrams for a more comprehensive understanding.
The speaker mentions that future videos will apply the concepts discussed in the series to real-world forecasting scenarios.
The speaker explains the difference between calling a wind a "southerly wind" (coming from the south) and a "northerly wind" (going towards the north).
The speaker emphasizes the importance of using a protractor and a straight edge when plotting a hodograph for accurate results.
The speaker acknowledges the difficulty in drawing overlapping vectors by hand and compares the hand-drawn hodograph to the actual hodograph generated from the raw data.
The speaker mentions that the next video will cover how to estimate quantities such as storm relative helicity and wind shear between different layers using the hodograph.
Transcripts
hey everybody trey here welcome to
another episode in this skew teen
hodograph series
up to this point we've talked pretty
extensively about this side of the
sounding diagram
now we're going to move on and take a
look at this side of the diagram which
is of course the hodograph
if you haven't checked out the
previous videos in the series on skutees
i would highly recommend doing so i'll
put the links to all those in the
description below but toward the end of
the series we're going to be doing some
kind of wrap up videos
taking what we've talked about in the
series and applying it to some real
world forecasting scenarios so
go ahead and check those out if you
haven't
but now we're going to move into talking
about the hodograph now what is the
hodograph well it's basically a visual
representation of the wind shear
in the atmosphere and we know that wind
shear
is the changing of wind speed and
direction with height
so
if you have you know 10 knots of wind at
the surface and then a kilometer above
that you have
let's say you know 50 knots of wind
that's wind shear that is
speed shear
you know if it's coming out of a
different direction say the wind at the
the surface is 10 knots out of the south
uh and the wind at a kilometer above
that is let's say 50 knots out of the
southwest you have both speed and
directional wind shear in that case so
the hodograph is a really
easy way
to help visualize the wind profile and
the shear profile in the atmosphere it's
a much simpler diagram than the skt it
doesn't have all those different lines
to follow
and it basically just takes into account
the wind direction and the wind speed
now some quick sort of you know basic
review before we go into
actually constructing a hodograph
from some raw data like we did with the
skew-t
we talk about winds
which can be
represented as vectors so a vector
is basically
a representation of the magnitude and
direction of a quantity
so if we have you know a 10 knot wind
from the west
that would the vector for that would
look like that we have a 50 knot wind
from the
west
the vector would be much longer showing
the increase in magnitude there
and we also we always talk about wind
in the direction that it's coming from
not the direction that it's going to so
whenever we say we have let's say a
southerly
wind
we're saying that that wind is coming
from the south
to the north we don't call that a
northerly wind because the wind is going
toward the north we call that a southern
southerly wind because it is coming from
the south
let's say we had a northwesterly wind
well that would be coming from the
northwest
toward the southeast
would be a northwesterly wind so keep
those things in mind as we talk about
the hodograph here coming up
so let's take a look at some raw data
here we're going to look do exactly what
we did with the sku ts
and looking at raw data and trying to
construct
a hodograph from the raw data
now we talked about all these variables
before in a previous video toward the
early portion of the series
to create a hodograph we're just we're
going to be focusing
on these two columns
right here
so we briefly touched on these in in
that video previously but these two
columns
are the data regarding the wind so this
one on the left
is wind direction
in degrees so
wind is given
um if we're doing it in raw data form
it's given in degrees so
if we create a grid
here
we're going to say
that
if when the wind is at zero degrees
it's coming from the due north so this
would be zero degrees
it's coming from the dew north
then we go around
clockwise so this would be 90 degrees
and an easterly wind so coming from the
east would be a 90 degree wind
coming from the dew south would be 180
degrees
and then coming from the due west would
be 270 degrees
and then finally if we have
back to our due northerly wind we can
call that zero degrees or
360 degrees
so that is how we
denote wind direction in degrees and
we'll talk about that a little bit more
when we look at how to plot this actual
hodograph
the column here on
the right
is the wind speed
in knots so it's measured in knots not
miles per hour pretty simple this is the
magnitude
and this is the direction
so let's say
talking about vectors we'll take this
wind here at the surface which is 190
degrees
at six knots
so 190 degrees at six knots
so this would be
coming at 190 degrees so just to the
left
just to the west of due south
so we would draw it from the origin
going up this way
six knots and we'll talk about how to
denote and how to
um properly denote the
speed
of each wind vector when we're when we
plot the hodograph here but it would
look something like this it's coming
from the southwest from the south
southwest just west of due south at 190
degrees
so we dropped from the origin
going up from the southwest
toward the northeast
at 190 degrees at six knots and we'll
talk about again how to denote the
speed the magnitude
in just a sec so we're going to focus on
these two columns here wind direction
and wind speed of course we're gonna
we're going to keep the
pressure level
in mind as we go through this exercise
so let's go ahead and plot a
sounding or plot this hodograph here so
this is going to be a different
hodograph than what we
then from from this raw data different
raw data than what we did
in i believe video two when we
constructed this qt from that raw data
this is a different set of raw data same
concepts here though
so i'm only going to plot
a few points here obviously the programs
that plot these hodographs are going to
plot every single point but in the
interest of time i'm going to
kind of just plot a few different points
and show you just the gist of how the
hodograph is made
so we have our raw data here on the left
and our blank hodograph on the right
now you might be thinking this looks
like a lot different than a normal graph
definitely different than the skewties
we've been looking at the past few
videos and that is because the hodograph
is given in polar coordinates so when
you see a normal graph
it is given in usually x y coordinates
it has an x-axis and a y-axis so if
you're measuring you know say distance
versus time
it's in cartesian coordinates you have
an x-axis and a y-axis
but wind is not given in x-y coordinates
wind is given in
it's a vector quantity given it has a
magnitude which is the wind speed
and a direction
and the wind speed
is referred to as r that's our magnitude
and our direction is
going to be referred to by the variable
theta which is basically just the angle
of the wind or the direction the wind is
coming from
so the coordinates the polar coordinates
are r theta so when we're looking at
this graph this hodograph is in polar
coordinates so
each spoke so each of these lines kind
of emanating from the origin
is a
different theta
so each of these is a different theta or
different angle different wind direction
so starts at the top at zero degrees
90 180 270 back to zero or 360.
and each of these rings here
is representative of our r-coordinate or
our wind speed now when you're making
your own hodograph
you can kind of pick your interval here
between the rings
i like to do 10. for this example i'm
going to do 10. so each ring increases
by 10 so 10 knots 20 knots 30 knots 40
knots
and so on
and then you get an interval of about 10
degrees between each spoke here or each
theta
so that is how you plot
the
that is the basis for the hodograph
diagram
so let's get started and plot some of
these wind vectors so i'm going to
scroll this down a little bit
and of course so we have our zero
degrees up here zero slash 360. just to
keep this kind of in in the back of our
minds this is going to be 90 degrees 180
degrees
and
270 degrees
so let's start at the surface here so
our surface here would be at 983
millibars about 173
meters off
uh off the ground
so we start with our
speed it's going to be
six knots at 190 degrees so our first
point here is six knots at 190 degrees
so
we're going to find 190 degrees so of
course do do southerly is going to be
180.
so this spoke here would be 190. so we
start at the origin
and we follow that
upward
six knots so of course we know that this
first ring is 10 knots so we're going to
go up just over halfway from the origin
between the origin and this first ring
kind of on that 190 degree
line and we're going to plot our wind
vector
so i'm going to going to do different
colors here kind of alternate
so we know what we're talking about so
i'm not going to do every single point
here of course the sounding programs
that plot the soundings from the raw
data are going to plot every single
point in the atmosphere i'm just going
to do a few different points here to
kind of get get you the gist
of how to do this
so let's do this one here at 935
millibars about 600 meters off the
ground
wind direction is 195
degrees 35 knots
so again we find 195 degrees it's going
to be between this spoke and this spoke
here it's about right in there
and we're going to go up 35 knots so
this one would be 10
20
30
35
so there's our end point
for our vector and we just simply draw
our vector
now in a
general
you know sense when you are making the
hodographs you would be using a
protractor using a straight edge
so that so that you get the most
accurate holograph possible here i'm
just going to kind of freehand it but
you kind of get the idea
so let's go up to let's go to 873
millibars here
which is just over a kilometer above
ground level so this
wind vector here speed 44 knots 210
degrees
so we find 210 degrees this is 190
200
210 so 210
at 44 knots so we go up along this
spoke here 10 20 30 40
44.
so our end point of our vector is going
to be there
and then we just draw the vector from
the origin
back
so let's do the next one in green here
let's go to
let's do this one here at about 8 11
millibars
so 49
knots 225 degrees so 225 again this is
190 200 210 220 230 so right in between
there
right in between those two
then we go out
what is going to be 49 knots so 10
20
30 40 50. so just short of the 50
line there
and we draw our vector
from the origin
back
so i'll do another one in green here
let's go
let's do
751 here
230
230 degrees 54 knots so we find 230 so
this was 225 so this one would be 230
10 20 30 40
50 60 so kind of right in the middle
there
back to the origin
i'm going to change colors here back to
blue let's do
let's go 700 millibars here
225 degrees it's 63 knots so we've
already found the 225 degree
one here
but now it's 63 not so 5 10 20 30 40 50
60
63 would be somewhere in there you draw
from the origin
along that 225 degree
let's do a couple more here let's go
let's do
i'm just going to skip a few in the
interest of time and space here on this
diagram so 500 millibars
would be 230 degrees at 80 knots so
we've already found 230 here
so again we're going to go
5 10 20 30 40 50 60 70 80.
so very strong winds here at 500
millibars
we draw our vector
once again
and then let's do
let's do one more here let's go to 400
240 degrees 84 knots so this is 230
240 would be over here we already know
that this is 80 so it'll be actually
just a little bit off the diagram here
and we draw our vectors so we've drawn
all of our wind vectors here
and now what we're going to do is we're
going to connect the tips of the vectors
and that is going to make our hodograph
so
we'll start here
and we're going to go up
connecting to the tip of the next vector
we go from the tip of that vector
to the
subsequent vector there
and then just do that
and keep doing that until we have our
hodograph then we went back here
a little bit
and then that is how you make a
hodograph so we made our hodograph here
a little bit messy here because it's you
know a little bit hard to draw you know
these kind of overlapping vectors
but if we go
to our actual
hodograph you can see we did a pretty
good job there it kind of starts off
increases in size then kind of goes back
toward the north here
as our wind vectors were a little bit
more southerly here in the mid levels a
couple a few kilometers up
then it goes back toward the east a
little bit so we did a pretty good job
with our hodograph and this is the
actual photograph for that raw data that
we plotted
and we can find a lot of different
quantities from this hodograph
we can find wind shear between different
levels we can find
stuff called called storm relative
helicity
storm motion etc and we'll talk about
how to find all of those parameters in
the next video so that's all i've got
for now that's kind of the basics of how
a hodograph works how you can create a
hodograph from raw data
again in the next video we'll talk about
how to how to kind of estimate different
quantities such as storm relative
felicity
um
wind shear between two different layers
uh etc so thanks for watching and we
will see you in the next video
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