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SO254 – Upper-air charts SO254 – Upper-air charts

SO254 – Upper-air charts - PowerPoint Presentation

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SO254 – Upper-air charts - PPT Presentation

Upperair circulation tied to the 3cell model We saw in Lesson 2 that differences in insolation more in the tropics less in the polar regions combined with the Earths rotation drives complex circulation patterns ID: 586449

pressure air upper 500 air pressure 500 upper surface lines level height temperature chart ridges winds source points troughs

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Slide1

SO254 – Upper-air chartsSlide2

Upper-air circulation tied to the 3-cell model

We saw in Lesson 2 that differences in insolation (more in the tropics, less in the polar regions), combined with the Earth’s rotation, drives complex circulation patterns

Three circulation cells develop: Hadley, Farrell, and Polar

Figure at the right shows average surface wind patternsWhat do the upper-level wind patterns look like?

Stull 2016Slide3

Upper-air circulation tied to the 3-cell model

In the

upper troposphere

, the three circulation cells are also seen:Hadley cell: tropical easterly winds, noted by HHHHadley/Farrell interaction: mid-latitude westerly windsSubtropical jet (noted by HH)Farrell/Polar cell interaction: Polar jet

The polar jet (and really, the subtropical jet and the tropical easterly winds, despite the lousy figure) is wavyWhat does that waviness mean for the weather at a particular place?

How can we identify the waviness?

Stull 2016Slide4

Upper-air circulation tied to radiative imbalance

Incoming radiative flux at top of the atmosphere (

E

insol) varies by latitudeRadiative flux that makes it into the atmosphere (not reflected) also varies by latitude (Ein)Outward radiative flux (Eout

, dashed line) also varies by latitude, but not as much as Ein or Einsol

Difference between outgoing and incoming (Enet) is positive in the tropics and negative poleward of about 33°N and 33 ° SThis difference in radiation drives global circulation

A difference in radiation between tropics and poles, along with the rotation of the Earth, is basically the reason why we have weather

Stull 2016Slide5

Upper-air analysis

You learned in the last lesson that the

thickness

of a layer of air depends on several things:The pressure of the top and bottom of the layerThe mean temperature of the layerThis relationship between thickness (Z2-Z1), mean temperature, and pressure is called the

hypsometric equationQuick example: calculate the thickness

of the air layer between 1000 mb and 500 mb if the mean temperature of that layer is freezing (273.15 K)

 

Stull 2016Slide6

More on thickness

One type of upper-air weather chart is one that shows horizontal variation in thickness

See example at right

A thickness chart is useful because it can combine information from two pressure levels (in the case of the figure at right, 1000 mb and 500 mb), as well as the temperature between those levelsBut, thickness charts have their limitations, because thicknesses have limitations

Which of these profiles, all of which have mean temperatures of 273.15K, might support snow?

GFS model forecast of

precip

type and intensity (color), sea level pressure (solid black lines), and 1000-500

mb

thickness (dashed lines), valid at 18Z (1 pm EST) 30 Jan 2017. Source: pivotalweather.com

0°C

0°C

0°C

0°C

0°C

1000

mb

850

mb

500

mb

700

mbSlide7

Height of the 500

mb

surface

(in meters): Elevation above sea level of the 500

mb

surface

If there are no horizontal temperature variations, 500

mb

surface will be mostly flat

**A FLAT SURFACE IS UNREALISTIC**

(Where on the Earth might a flat 500-mb surface actually be realistic?)

Developing a concept of the upper-level chartSlide8

Developing a concept of the upper-level chart

How do we know the height of the 500-mb pressure level?

Radiosondes!!

https://www.youtube.com/watch?v=AoUxq4mTv5M

Value of radiosondes to 24-h weather forecasts (and compared to other data types).

Source: NASA

https://gmao.gsfc.nasa.gov/forecasts/systems/fp/obs_impact/

Where are radiosondes typically launched? Source: ECMWF

What is in the instrument?

Source: Plymouth State

UnivSlide9

In the real atmosphere, horizontal temperature variability does exist.

In the figure at right, “south” is closer to the equator and “north” is closer to the pole

Because warm air occupies more space, the 500

mb

surface will be:

- higher in warm air

- lower in cold air

The hypsometric equation can also be used to show this relationship:

Let the pressure at the ground be 1000

mb

everywhere. Then the distance between the ground and the 500-mb surface depends on the temperature of the layer

Developing a concept of the upper-level chartSlide10

When there are horizontal variations in temperature, the constant-pressure surface will slope (not be flat)

The degree of the slope depends on temperature of the air column below it

Resulting chart plots

heights

of pressure surface

Called a “constant pressure chart”The charts are more commonly referred to by the pressure level you are showing

Ie

, the “500-mb pressure chart” or the “500-mb chart”

On a two-dimensional chart (like shown at the bottom of the figure at right), the greater the slope of the pressure surface, the closer the lines are

Closer lines indicate tighter

height gradients

We will see later in the course that the height gradient is one of the main reasons why air moves

Developing a concept of the upper-level chartSlide11

Developing a concept of the upper-level chart

The

constant pressure surface

Is three-dimensional

Its shape (generally) depends on the temperature of the air below it

“Ridges”

indicate regions of higher heights

should correspond to regions of warmer air

“Troughs”

indicate regions of lower heights

should correspond to regions of colder air

In the figure at right, look at how the 3-d pressure surface (colored) shows up on a 2-d chart. Note how the heights at 500-mb look on the chart

The base state would have flat, east-west lines, with no curves. That would mean isothermal conditions (constant temperatures)

A chart with ridges and troughs implies temperature variations

Ridges are where heights are higher relative to nearby values

Troughs are where heights are lower relative to nearby heightsSlide12

Let’s look at real examples of pressure surfaces from today and try to identify troughs and ridges

http://www.pivotalweather.com/model.php?m=gfs&p=700wh

http://www.pivotalweather.com/model.php?m=gfs&p=500wh

http://www.pivotalweather.com/model.php?m=gfs&p=300wh

http://www.pivotalweather.com/model.php?m=gfs&p=850wh

Source:

Univ

of ArizonaSlide13

Another example to connect the 3-d, wavy upper-air surface to a 2-dimensional chart

Figure at right shows the 850-mb pressure surface

Note that the ridge and trough are both associated with temperatures

Ridge: warmer temperaturesTrough: colder temperaturesNotice too, that the temperatures vary within the ridge and troughWarmest temperatures are found at the “base” (most equatorward part) of the ridge

Coldest temperatures are found in the core of the trough

Source:

Univ

of ArizonaSlide14

Some general properties of troughs and ridges

Warmer air in ridges, colder air in troughs

The warm and cold air masses are often deep, occupying most of the column of air in the ridge and trough, respectively

At the level of the upper-air chart, temperatures in the trough are also often colder than temperatures in the ridgeHowever, because the height of the trough and ridge depends more on the temperature of the layer, and not on the temperature exactly at the pressure level being contoured, the pattern of cold and warm temps can varyWinds are usually parallel to height lines

If lines are curved, winds in gradient balance will be parallel to the height linesIf lines are straight (east-west or north-south), winds in

geostrophic balance will be parallel to the height lines

Source:

Univ

of ArizonaSlide15

Quick knowledge check

Is the pressure at Point C greater than, less than, or equal to the pressure at Point D (you can assume that Points C and D are at the same latitude)?  How do the pressures at Points A and C compare?

Which of the four points (A, B, C, or D) is found at the lowest altitude above the ground, or are all four points found at the same altitude?

The coldest air would probably be found below which of the four points?  Where would the warmest air be found?

What direction would the winds be blowing at Point C?

Source:

Univ

of ArizonaSlide16

Quick knowledge check

Is the pressure at Point C greater than, less than, or equal to the pressure at Point D (you can assume that Points C and D are at the same latitude)?  How do the pressures at Points A and C compare?

Pressure at all 4 points is the same.

This is the 500-mb chart

Which of the four points (A, B, C, or D) is found at the lowest altitude above the ground, or are all four points found at the same altitude?

Point A is lowest (5400 m), points B and C are same (5520 m) and point D is highest (5640 m)

The coldest air would probably be found below which of the four points? 

Where would the warmest air be found?

Coldest air would most likely be found at A, and warmest air most likely at D

What direction would the winds be blowing at Point C?

Winds at C should be from W to E (so “westerly winds”). Winds at A would also be westerly, as at B and D.

Source:

Univ

of ArizonaSlide17

What do troughs and ridges look like in the Southern Hemisphere?

Troughs are defined as lower heights, relative to nearby values, and ridges are defined as higher heights, relative to nearby values

Generally, air is warmer closer to the equator and cooler closer to the poles

Thus, when cooler air extends from the pole toward the equator, it typically shows up as a troughSimilarly, when warmer air from the equator extends poleward, it typically shows up as a ridge

Source:

Univ

of ArizonaSlide18

What do troughs and ridges look like in the Southern Hemisphere?

Where are the troughs and ridges in this 500-mb chart?

Where are the troughs and ridges in this 500-mb chart?

Source:

http://wxmaps.org/fcst.php

Slide19

A three-dimensional perspective

We’ll see much more about this later in the semester

For now, important to remember that upper-level troughs and ridges are directly related to surface features like fronts, pressure systems and the like

In synoptic theory, the upper-level waves tend to project onto the surface, then receive feedback from the surface.It’s rare to see surface features in-absentia (eg, apart from upper-level “support” or “forcing”)

Source:

Univ

of ArizonaSlide20

A three-dimensional perspective

Another example of the connection between the surface (sea level pressure isobars, top panel), the thickness (dashed 1000-500

mb

thickness lines, middle panel) and upper-air height (solid height lines at 500 mb, bottom panel)What patterns do you notice in common between the three figures?What features connect across the figures? What features do not seem to connect?

Stull 2016Slide21

A three-dimensional perspective

Returning to the 3-cell model: the polar jet (boundary between polar cell and Farrell cell)

The polar jet intensity and location depends heavily on differences between temperature (thickness) between the polar and mid-latitude regions

Stull 2016Slide22

What differences do you notice between the winter (top panel) and summer (bottom panel) hemispheres?

A three-dimensional perspective

Stull 2016Slide23

Important role of troughs and ridges: heat redistribution

As you know from the radiation lesson, because the Earth is a sphere, more radiation reaches the middle portion of the planet (the tropics) than the poles

Upper-air waves are the main way the planet re-distributes that heat

Move warm air poleward and cold air equatorwardFigure 11.60 (lower left) indicates that total heat redistribution (dark black curve) is mostly due to atmospheric waves, then secondarily due to ocean circulation, and finally due to Hadley and polar cells

Stull 2016Slide24

Important properties of upper-air charts

Heights related to temperature of the layer (via the hypsometric equation): taller heights imply warmer layers

Above the surface of the Earth, winds generally blow parallel to height lines

When winds blow parallel to the heights, and the height lines are straight (eg, no curvature), the wind is said to be in “geostrophic balance.”Geostrophic balance is one of the most important balances in all of meteorology and oceanographyYou will hear about geostrophic balance many, many, many more times in your courses. In fact, it is named in the Department Learning Objectives as one of the most important things you will learn about in the major!

What, then, is in balance? Pressure gradient force

Coriolis forceWhen the height lines are curved, winds still typically blow parallel to the lines. This is called “gradient balance”What is in balance in gradient balance? Pressure gradient force, Coriolis force, and centrifugal force

Near the surface of the Earth, friction plays an important role and causes winds to cross (intersect with) height linesSlide25

Utility of charts at different pressure levels

850mb

: to identify fronts

700mb: intersects many clouds; moisture information is important : intersects many clouds; moisture information is important 500mb: used to determine the location of short waves and long waves associated with the ridges and troughs in the flow pattern. waves associated with the ridges and troughs in the flow pattern. Meteorologists examine “vorticity” (i.e. rotation of air) on this pressure level.

300, 250, and 200mb

: near the top of the troposphere or the lower stratosphere; these maps are used to identify the location of jetsreams that steer the movements of mid latitude storms

Source:

Univ

California IrvineSlide26

Why manual analysis?

Tremendous amount of weather data available today when compared to 1950s (1950s are considered the start of modern meteorology)

Automated techniques are pretty good at plotting

isolines of anythingTemperature, pressure, dew point, precipitation, height, etc.But … to understand & synthesize the data in the charts requires the meteorologist to examine the actual observations (and it requires patience)A manual analysis requires a meteorologist to look at

every data point! Time consuming, yes. So is it valuable?Tremendous benefit in being forced to think about observational data and interpret weather observationsSlide27

Manual analysis: upper-air

Important to also examine weather observations above the surface of the earth

Typically examine constant-pressure charts

250 mb, 500 mb, 700 mb, and 850 mbHeight contours almost always parallel to winds (i.e., geostrophic balance)Temperature gradients tend to not be as sharp above 700

mbExample: at the surface in winter, Florida can have temps near 30C (mid-80s F) and New York near -10C (mid-10s F), while at 500

mb, temps near -10C over FL may only decrease to -20C over NY.Slide28

How to conduct an upper-air analysis: contour intervals

250

mb

: Contour every 60 mBe sure to include 10800 m – so 10860, 10920, 10740, etc.500

mb: Also contour every 60 mBe sure to include 5400 m – so 5460, 5520, 5340, etc.

700 mb: Contour every 30 m

Be sure to include 3000 m – so 3030, 3060, 2970, etc.

850

mb

: Also contour every 30 m

Be sure to include 1500 m – so 1530, 1560, 1470, etc.Slide29

Rules of

Isoplething

Never violate a valid data point. Only in extreme and defendable circumstances should data be omitted. Analyze for all given data.

Interpolate as much as possible. Allow for extreme packing of isolines if that is defendable.Smooth isolines and, whenever possible, keep pacing consistent.

Do not analyze for what does not exist. Do not assume data.There should be no features smaller than the distance between data points.Isolines

cannot intersect nor can they suddenly stop. Just as data is continuous, so are isolines. The exception to this is naturally at the end of a page.Label all closed

isolines

with appropriate markings (i.e. "H" or "L") in bold and large letters. Label the maximum and minimum values with a small underline.

Label the ends of the lines neatly and consistently. Make sure that any abbreviations are understandable. Title the map and include time.

Analyze in even multiples of the interval of analysis.

Remember that each line must represent all areas with the specified value. On one side of the line, values will be lower than the value on the line and on the other side, values will be higher.

Use a good pencil and initially sketch lines lightly. If needed, make them smooth by darkening the lines after you know where they should be placed.

Have a good eraser handy.

Start with a line that gives you a good understanding of what is happening. This may be in the middle or near the extremes. Use this line as a guide to draw the rest of the

isolines

.

When the lines become tricky to draw, consider all the alternatives. There may be a better way to draw the analysis.

Remember that the data is only a reflection of the actual atmosphere!

Adapted from College of

DuPage

http://weather.cod.edu/labs/isoplething/isoplething.rules.html