* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Lesson 04
Survey
Document related concepts
Lockheed WC-130 wikipedia , lookup
Global Energy and Water Cycle Experiment wikipedia , lookup
Atmospheric model wikipedia , lookup
Air well (condenser) wikipedia , lookup
Tectonic–climatic interaction wikipedia , lookup
Cold-air damming wikipedia , lookup
Atmosphere of Earth wikipedia , lookup
Weather lore wikipedia , lookup
Instrumental temperature record wikipedia , lookup
Pangean megamonsoon wikipedia , lookup
Atmospheric convection wikipedia , lookup
Transcript
SO254 – Upper-air charts 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 patterns • What do the upper-level wind patterns look like? Stull 2016 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 HHH • Hadley/Farrell interaction: midlatitude westerly winds • Subtropical 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 wavy • What does that waviness mean for the weather at a particular place? • How can we identify the waviness? Stull 2016 Upper-air circulation tied to radiative imbalance • Incoming radiative flux at top of the atmosphere (Einsol) varies by latitude • Radiative 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 ° S • This 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 2016 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 layer • The mean temperature of the layer • This relationship between thickness (Z2-Z1), mean temperature, and pressure is called the hypsometric equation 𝑅𝑇 𝑝1 𝑍2 − 𝑍1 = ln 𝑔0 𝑝2 • Quick 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 2016 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 levels • But, 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? 500 mb 700 mb 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 850 mb 1000 mb 0°C 0°C 0°C 0°C 0°C Developing a concept of the upper-level chart 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 chart • How do we know the height of the 500-mb pressure level? • Radiosondes!! https://www.youtube.com/watch?v=AoUxq4mTv5M What is in the instrument? Source: Plymouth State Univ Value of radiosondes to 24-h weather forecasts (and compared to other data types). Source: NASA Where are radiosondes typically launched? Source: ECMWF https://gmao.gsfc.nasa.gov/forecasts/systems/fp/obs_impact/ Developing a concept of the upper-level chart • 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 chart • 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 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 heights 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=300wh http://www.pivotalweather.com/model.php?m=gfs&p=500wh http://www.pivotalweather.com/model.php?m=gfs&p=700wh http://www.pivotalweather.com/model.php?m=gfs&p=850wh Source: Univ of Arizona 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 temperatures • Trough: colder temperatures • Notice too, that the temperatures vary within the ridge and trough • Warmest 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 Arizona 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 ridge • However, 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 vary • Winds are usually parallel to height lines • If lines are curved, winds in gradient balance will be parallel to the height lines • If lines are straight (east-west or north-south), winds in geostrophic balance will be parallel to the height lines Source: Univ of Arizona 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? Source: Univ of Arizona What direction would the winds be blowing at Point C? 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 500mb 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 Source: Univ of Arizona 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. 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 trough • Similarly, when warmer air from the equator extends poleward, it typically shows up as a ridge Source: Univ of Arizona What do troughs and ridges look like in the Southern Hemisphere? Source: http://wxmaps.org/fcst.php Where are the troughs and ridges in this 500-mb chart? Where are the troughs and ridges in this 500-mb chart? 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 upperlevel 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 Arizona 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 2016 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 midlatitude regions Stull 2016 A three-dimensional perspective • What differences do you notice between the winter (top panel) and summer (bottom panel) hemispheres? Stull 2016 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 equatorward • Figure 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 2016 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 oceanography • You 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 force • When 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 lines 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 Irvine 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 anything • Temperature, 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 observations 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 mb • Height contours almost always parallel to winds (i.e., geostrophic balance) • Temperature gradients tend to not be as sharp above 700 mb • Example: 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. How to conduct an upper-air analysis: contour intervals • 250 mb: Contour every 60 m • Be sure to include 10800 m – so 10860, 10920, 10740, etc. • 500 mb: Also contour every 60 m • Be 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. 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