Definitive Guide to Skew-Ts and Hodographs - Part 6 - Hodograph Basics

Summary

This 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

00:00

🌀 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.

05:01

🔢 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.

10:01

📐 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.

15:03

🔄 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.

Keywords

💡Hodograph

A hodograph is a graphical representation of the wind vector (speed and direction) at various heights in the atmosphere. It provides a visual depiction of the wind shear, which is the change in wind speed and direction with height. In the video, the hodograph is introduced as a simpler diagram than the skew-T diagram, focusing solely on wind direction and speed. The process of constructing a hodograph from raw data is demonstrated.

💡Wind Shear

Wind shear refers to the change or variation in wind speed and/or wind direction over a given distance in the atmosphere. It is a crucial concept in meteorology as it can influence the behavior of storms and aircraft. The video emphasizes that the hodograph is a tool to visualize the wind shear profile, as it shows the changing wind vectors at different heights. Examples of wind shear are provided, such as a wind speed increase from 10 knots at the surface to 50 knots at 1 kilometer altitude.

💡Vector

A vector is a quantity that has both magnitude (numerical value) and direction. Wind is represented as a vector, with the wind speed being the magnitude and the wind direction being the directional component. The video explains that vectors are used to depict winds, with longer vectors representing higher wind speeds. It also clarifies that wind direction is always described based on the direction from which the wind is blowing, not the direction it is going towards.

💡Polar Coordinates

Polar coordinates are a coordinate system used to represent points on a plane using a radial distance (r) and an angle (theta) from a fixed reference point. The hodograph is plotted in polar coordinates, where the rings represent wind speed (r) and the spokes represent wind direction (theta). The video explains that this coordinate system is different from the typical Cartesian (x-y) coordinate system used for other graphs.

💡Wind Direction

Wind direction is the compass direction from which the wind is blowing, measured in degrees. In the video, wind direction is shown to be one of the two crucial components (along with wind speed) required to construct a hodograph. The wind direction data is provided in degrees, with 0° representing a wind from the north, 90° from the east, 180° from the south, and 270° from the west. The video demonstrates how to plot wind vectors using the direction and speed data.

💡Wind Speed

Wind speed is the rate of motion of the air, typically measured in knots (for meteorological purposes) or miles/kilometers per hour. It represents the magnitude or strength of the wind vector. In the video, the wind speed data is provided in knots, and it is shown how to plot wind vectors on the hodograph by using the wind speed as the radial distance from the origin along the corresponding wind direction.

💡Raw Data

Raw data refers to the unprocessed, numerical information collected from various meteorological instruments and observations. In the context of the video, raw data includes the wind direction (in degrees) and wind speed (in knots) at different pressure levels or altitudes in the atmosphere. The video demonstrates how to construct a hodograph by plotting wind vectors using the raw data values.

💡Skew-T Diagram

A skew-T diagram, also known as a sounding diagram, is a specialized meteorological diagram that displays vertical profiles of various atmospheric variables, such as temperature, dew point, and wind. The video contrasts the hodograph with the skew-T diagram, describing the hodograph as a simpler diagram that focuses solely on wind direction and speed, as opposed to the skew-T's multiple lines representing different atmospheric parameters.

💡Storm Relative Helicity

Storm relative helicity (SRH) is a measure of the potential for cyclonic updraft rotation in a thunderstorm. It is calculated by integrating the storm-relative wind vectors over a given layer of the atmosphere. The video mentions that SRH is one of the quantities that can be derived from the information displayed on a hodograph, suggesting that hodographs are useful tools in assessing the potential for severe thunderstorm development.

💡Storm Motion

Storm motion refers to the direction and speed at which a thunderstorm or other weather system is moving. The video briefly states that storm motion is another parameter that can be estimated from the information contained in a hodograph. Accurate forecasting of storm motion is crucial for predicting the areas that may be impacted by severe weather events.

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