DOCSLIB.ORG

Surface Air Pressure Patterns and Winds Applications

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Surface Air Pressure Patterns and Winds Applications Investigation 1B Surface Air Pressure Patterns and Winds Applications In the late-summer of 2020, weather across much of the contiguous U.S. had been quite warm. In some western locations, however, it was stifling, with fires raging and Death Valley, CA temperatures cresting at a scorching 130°F. Central and western states were dominated by large areas of high pressure with numerous Heat Warnings and Heat Advisories issued by the National Weather Service. Wildfires prompted hasty evacuations, while mitigation efforts were immensely challenging for firefighters. Weather conditions on the East Coast weren’t nearly as warm, and with lower pressure, more moisture abounded, bringing precipitation throughout New England and Florida. The Southeast experienced classic, late summer weather with bouts of small, slow-moving thunder- storms. Many of these storms were found proximate to fronts that didn’t surge far enough to cool off temperatures. The weather data for this investigation show a weak wind field, bereft of strong low-pres- sure systems. This is typical of late-summer weather patterns across the U.S. Figure 1B-1 (Pressures), acquired from Weather Studies Maps & Links, reports surface air pressure (corrected to sea level) rounded to the nearest whole millibar (mb) on 18 August 2020 at 17Z. UTC, or Z time, is four hours ahead of Eastern Daylight Time (EDT), so the 17Z map of August 18 depicts condi- tions at local times of 1 p.m. EDT (12 p.m. CDT, 11 a.m. MDT, 10 a.m. PDT, etc.). Figure 1B-1. Map of surface atmospheric pressure at selected stations at 17Z 18 AUG 2020. We recom- mend clicking on the map to view and print a full size image to analyze. Most weather map products from the Weather Studies Maps & Links are created by the National Weather Service’s (NWS) National Centers for Environmental Prediction (NCEP) at the National Oceanic and Atmospheric Administration (NOAA), as noted in the lower image margin: Unidata/NWS/NOAA. As the course proceeds, we will discuss the geographic regions across the United States. For your refer- ence, common NWS terminology for these are found at Link 1B-1 and Link 1B-2. 1. The highest plotted air pressure observed on the map of 1022 mb is located in ______. a. Texas b. California c. Florida d. Nebraska 2. The lowest reported pressure was ______ mb, in the Canadian province of Quebec (north of New England). a. 1007 b. 1010 c. 1013 d. 1016 3. The isobars in the conventional series to complete the pressure analysis between the lowest and high- est values on this map are ______ mb. a. 998, 1002, 1006, 1010 b. 999, 1003, 1007, 1011 c. 1008, 1012, 1016, 1020 d. 1013, 1018, 1023, 1028 To complete the isobars in Figure 1B-1, refer to the Tips on Drawing Isobars in Investigation 1A. More than one isobar of the same value should be drawn if pressure values located in separate sections of the map require it. Consider each pressure value at the center of the number. Isobars with values of 1008, 1012 and 1016 mb have already been started but look for other areas that require the additional 1016 and/or 1020 intervals as well. The labels for the isobars are added at the end of the land mass or at the map’s boundary. For closed isobar references in a circle, the number is placed in the line itself. Draw and label isobars of the series where they existed over the remaining portions of the U.S. and Canada. (Some isobars were intentionally left incomplete.) After completing all the isobars, label the positions with the lowest value in the U.S. mid-section with bold Ls. Label the highest pressure in the southeastern U.S. with an H. 4. In Pennsylvania, the 1012-isobar bisects the state near Williamsport with a line running north-south. Given the 4-mb interval convention, this line will separate values where the lower values on the map remain to one side while higher values are on the other side. The pressure values of locations west of Williamsport are ______ 1012 mb. a. less than b. equal to c. greater than Figure 1B-2 is the analyzed surface pressure map from Weather Studies Maps & Links produced from NOAA’s National Centers for Environmental Prediction (NCEP) for 17Z 18 August 2020. It shows the locations of isobars, air pressure system centers, and fronts at 15Z, 2 hrs before those on the Figure 1B- 1. Compare your analyzed map to Figure 1B-2. Note, the uniform dark green in Kansas, Oklahoma, and Texas are mostly “false returns” from the NOAA weather radar network. Figure 1B-2. Analyzed NCEP surface weather map for 17Z 18 AUG 2020 with isobars (blue lines), pressure systems, and precipitation. 5. The overall isobar patterns on the two maps over the coterminous U.S., particularly for the Great Lakes Low and the central High, are generally ______. Also included are shadings for precipitation around the country based on radar reports. a. very different b. similar The isobars in Figure 1B-2 are computer generated and based on a more complete set of pressure values than those in Figure 1B-1. This degree of detail can be seen, for example, on a near real-time surface map available from Link 1B-3. (This resolution may account for some of the variations between your analysis and Figure 1B-2. The computer-based analysis is the source of some additional plotted Hs de- noting more local marginally higher-pressure centers and Ls for lower pressure centers.) By analyzing the pressure values reported on weather maps to find pressure patterns, you can locate the centers of local highest and lowest pressures. We will see that these pressure centers often mark the mid- points of major weather systems, either regions of fair weather or stormy conditions, respectively. Figure 1B-3 is the “U.S. - Data” map from the Weather Studies Maps & Links, Surface Maps, for 17Z 18 August 2020. The data depict weather conditions at individual locations across the contiguous U.S. plotted using a coded format called the “surface station model.” Station models will be examined in more detail in Investigation 2A. Figure 1B-3. Unanalyzed NCEP surface weather map for 17Z 18 AUG 2020 with station model plots con- veying surface weather observations of temperature, moisture, pressure, cloud cover, wind speed and direc- tion. The centers of major high- and low-pressure systems are depicted with letters H and L respectively. Selected weather-reporting stations are shown on the map as circles and the wind directions shown by a line, which can be thought of as an arrow shaft, depicting the air flowinto each circle. In meteorology, wind at a station is identified by the direction the air is flowingfrom . (Air arriving at the station from the north is called a north wind.) 6. Therefore, the wind direction at Grand Junction, in western Colorado was generally from the ______. (Because of the map projection used, the north may not be precisely at the top of the map. In the Colorado area, a north-south line would be nearly parallel to the Colorado-Utah straight-line border.) a. north b. south c. west d. east 7. Knowing the direction from which the wind at Grand Junction was blowing, it would be reported as a(n) ______ wind. a. north b. south c. west d. east Optional: One knot (1 kt = 1 nautical mile per hour = 1 NM/hr) is about 1.2 land (statute) miles per hour. Wind speed is reported by a combination of long (10 kts) and short (5 kts) “feathers” attached to the direction shaft. Grand Junction had a 5-kt wind (one short feather). A double circle without a direction shaft, such as seen in Brownsville, TX, Denver, CO, and Reno, NV, signifies calm conditions. A shaft plotted without feathers would denote 1–2 kts. One tool for wind speed conversions between miles per hour and knots (as well as other quantities) and their formulas can be found at Link 1B-4. 8. Three bold blue Hs are marked on the map for the centers of high pressure. Compare the hand-twist model (Link 1B-5) of a High to the wind directions at stations in the several-state area flanking the high-pressure centers. (The central H is a slightly better example due to a lesser topographic influ- ence.) Wind direction at these stations suggest that, as seen from above in Figure 1B-3, the air was circulating ______ around the Northern Hemisphere high-pressure center. a. clockwise b. counterclockwise 9. The winds at stations in the states around the high-pressure center indicated the air also spiraled ______ the high-pressure center. a. outward from b. inward toward 10. This wind flow pattern, with respect to the high center, is therefore ______ thehand-twist model of a High. (Refer to Investigation 1A in the Manual for the hand-twist models of Lows and Highs.) a. contrary to b. consistent with In addition to the forcings of large-scale pressure patterns in the western portion of the country, air flows are influenced by the mountainous, high-elevation terrain that stretches from western Montana and Idaho southeastward to New Mexico and western Texas. As such, wind flow patterns around the high-pressure system may not fully display the anticipated rotation. Link 1B-6 dynamically displays the forecast wind flow in both direction and speed across the U.S. Mov- ing your cursor across the map will give the wind speeds at specific locations.
Load more

Recommended publications
  • Weather Maps
    Name: ______________________________________ Date: ________________________ Student Exploration: Weather Maps Vocabulary: air mass, air pressure, cold front, high-pressure system, knot, low-pressure system, precipitation, warm front Prior Knowledge Questions (Do these BEFORE using the Gizmo.) 1. How would you describe your weather today? ____________________________________ _________________________________________________________________________ 2. What information is important to include when you are describing the weather? __________ _________________________________________________________________________ Gizmo Warm-up Data on weather conditions is gathered from weather stations all over the world. This information is combined with satellite and radar images to create weather maps that show current conditions. With the Weather Maps Gizmo, you will use this information to interpret a variety of common weather patterns. A weather station symbol, shown at right, summarizes the weather conditions at a location. 1. The amount of cloud cover is shown by filling in the circle. A black circle indicates completely overcast conditions, while a white circle indicates a clear sky. What percentage of cloud cover is indicated on the symbol above? ____________________ 2. Look at the “tail” that is sticking out from the circle. The tail points to where the wind is coming from. If the tail points north, a north wind is moving from north to south. What direction is the wind coming from on the symbol above? ________________________ 3. The “feathers” that stick out from the tail indicate the wind speed in knots. (1 knot = 1.151 miles per hour.) A short feather represents 5 knots (5.75 mph), a long feather represents 10 knots (11.51 mph), and a triangular feather stands for 50 knots (57.54 mph).
    [Show full text]
  • NWS Unified Surface Analysis Manual
    Unified Surface Analysis Manual Weather Prediction Center Ocean Prediction Center National Hurricane Center Honolulu Forecast Office November 21, 2013 Table of Contents Chapter 1: Surface Analysis – Its History at the Analysis Centers…………….3 Chapter 2: Datasets available for creation of the Unified Analysis………...…..5 Chapter 3: The Unified Surface Analysis and related features.……….……….19 Chapter 4: Creation/Merging of the Unified Surface Analysis………….……..24 Chapter 5: Bibliography………………………………………………….…….30 Appendix A: Unified Graphics Legend showing Ocean Center symbols.….…33 2 Chapter 1: Surface Analysis – Its History at the Analysis Centers 1. INTRODUCTION Since 1942, surface analyses produced by several different offices within the U.S. Weather Bureau (USWB) and the National Oceanic and Atmospheric Administration’s (NOAA’s) National Weather Service (NWS) were generally based on the Norwegian Cyclone Model (Bjerknes 1919) over land, and in recent decades, the Shapiro-Keyser Model over the mid-latitudes of the ocean. The graphic below shows a typical evolution according to both models of cyclone development. Conceptual models of cyclone evolution showing lower-tropospheric (e.g., 850-hPa) geopotential height and fronts (top), and lower-tropospheric potential temperature (bottom). (a) Norwegian cyclone model: (I) incipient frontal cyclone, (II) and (III) narrowing warm sector, (IV) occlusion; (b) Shapiro–Keyser cyclone model: (I) incipient frontal cyclone, (II) frontal fracture, (III) frontal T-bone and bent-back front, (IV) frontal T-bone and warm seclusion. Panel (b) is adapted from Shapiro and Keyser (1990) , their FIG. 10.27 ) to enhance the zonal elongation of the cyclone and fronts and to reflect the continued existence of the frontal T-bone in stage IV.
    [Show full text]
  • Chapter 4: Pressure and Wind
    ChapterChapter 4:4: PressurePressure andand WindWind Pressure, Measurement, Distribution Hydrostatic Balance Pressure Gradient and Coriolis Force Geostrophic Balance Upper and Near-Surface Winds ESS5 Prof. Jin-Yi Yu OneOne AtmosphericAtmospheric PressurePressure The average air pressure at sea level is equivalent to the pressure produced by a column of water about 10 meters (or about 76 cm of mercury column). This standard atmosphere pressure is often expressed as 1013 mb (millibars), which means a pressure of about 1 kilogram per square centimeter (from The Blue Planet) 2 (14.7lbs/in ). ESS5 Prof. Jin-Yi Yu UnitsUnits ofof AtmosphericAtmospheric PressurePressure Pascal (Pa): a SI (Systeme Internationale) unit for air pressure. 1 Pa = force of 1 newton acting on a surface of one square meter 1 hectopascal (hPa) = 1 millibar (mb) [hecto = one hundred =100] Bar: a more popular unit for air pressure. 1 bar = 1000 hPa = 1000 mb One atmospheric pressure = standard value of atmospheric pressure at lea level = 1013.25 mb = 1013.25 hPa. ESS5 Prof. Jin-Yi Yu MeasurementMeasurement ofof AtmosAtmos.. PressurePressure Mercury Barometers – Height of mercury indicates downward force of air pressure – Three barometric corrections must be made to ensure homogeneity of pressure readings – First corrects for elevation, the second for air temperature (affects density of mercury), and the third involves a slight correction for gravity with latitude Aneroid Barometers – Use a collapsible chamber which compresses proportionally to air pressure – Requires only an initial adjustment for ESS5 elevation Prof. Jin-Yi Yu PressurePressure CorrectionCorrection forfor ElevationElevation Pressure decreases with height. Recording actual pressures may be misleading as a result.
    [Show full text]
  • Anticyclones
    Anticyclones Background Information for Teachers “High and Dry” A high pressure system, also known as an anticyclone, occurs when the weather is dominated by stable conditions. Under an anticyclone air is descending, maybe linked to the large scale pattern of ascent and descent associated with the Global Atmospheric Circulation, or because of a more localized pattern of ascent and descent. As shown in the diagram below, when air is sinking, more air is drawn in at the top of the troposphere to take its place and the sinking air diverges at the surface. The diverging air is slowed down by friction, but the air converging at the top isn’t – so the total amount of air in the area increases and the pressure rises. More for Teachers – Anticyclones Sinking air gets warmer as it sinks, the rate of evaporation increases and cloud formation is inhibited, so the weather is usually clear with only small amounts of cloud cover. In winter the clear, settled conditions and light winds associated with anticyclones can lead to frost. The clear skies allow heat to be lost from the surface of the Earth by radiation, allowing temperatures to fall steadily overnight, leading to air or ground frosts. In 2013, persistent High pressure led to cold temperatures which caused particular problems for hill sheep farmers, with sheep lambing into snow. In summer the clear settled conditions associated with anticyclones can bring long sunny days and warm temperatures. The weather is normally dry, although occasionally, localized patches of very hot ground temperatures can trigger thunderstorms. An anticyclone situated over the UK or near continent usually brings warm, fine weather.
    [Show full text]
  • Anticyclones – High Pressure Task 11 A: Read the Notes on High Pressure
    Anticyclones – High pressure Task 11 A: Read the notes on high pressure. B: Watch the video clip on Anticyclones and sing along! C: Write out the information and fill in the blanks. D: Print/ sketch the diagram and add the labels. E: Using the information on summer and winter anticyclones, fill in the table to identify how they are similar and different in summer and winter F: Write a paragraph describing the hazards for people that are created by summer and winter anticyclones. G: Watch the two video clips on the 2003 European heatwave and write down 10 facts you have learned. H: Quiz, is it an anticyclone or a depression? I: Complete the grid comparing anticyclones and depressions. A WHAT CAUSES HIGH PRESSURE? • When air high in the atmosphere is cold, it falls towards the earth’s surface. • Falling air increases the weight of air pressing down on the Earth’s surface. • This means that air pressure is high • Because the air is falling, not rising there is no clouds forming • A high pressure system is called an ANTICYCLONE. B https://www.youtube.com/watch?v=FCz8J_mxswg C Anticyclones • Anticyclones are areas of high pressure in the atmosphere, where the air is sinking. • High pressure brings settled weather with clear,, bright skies. • As the air is sinking, not rising, no clouds or rain can form. • Winds may be very light . • In summer anticyclones bring dry, hot weather. • High pressure systems are slow moving and can persist over an area for a long period of time, such as days or weeks.
    [Show full text]
  • Synoptic Meteorology
    Lecture Notes on Synoptic Meteorology For Integrated Meteorological Training Course By Dr. Prakash Khare Scientist E India Meteorological Department Meteorological Training Institute Pashan,Pune-8 186 IMTC SYLLABUS OF SYNOPTIC METEOROLOGY (FOR DIRECT RECRUITED S.A’S OF IMD) Theory (25 Periods) ❖ Scales of weather systems; Network of Observatories; Surface, upper air; special observations (satellite, radar, aircraft etc.); analysis of fields of meteorological elements on synoptic charts; Vertical time / cross sections and their analysis. ❖ Wind and pressure analysis: Isobars on level surface and contours on constant pressure surface. Isotherms, thickness field; examples of geostrophic, gradient and thermal winds: slope of pressure system, streamline and Isotachs analysis. ❖ Western disturbance and its structure and associated weather, Waves in mid-latitude westerlies. ❖ Thunderstorm and severe local storm, synoptic conditions favourable for thunderstorm, concepts of triggering mechanism, conditional instability; Norwesters, dust storm, hail storm. Squall, tornado, microburst/cloudburst, landslide. ❖ Indian summer monsoon; S.W. Monsoon onset: semi permanent systems, Active and break monsoon, Monsoon depressions: MTC; Offshore troughs/vortices. Influence of extra tropical troughs and typhoons in northwest Pacific; withdrawal of S.W. Monsoon, Northeast monsoon, ❖ Tropical Cyclone: Life cycle, vertical and horizontal structure of TC, Its movement and intensification. Weather associated with TC. Easterly wave and its structure and associated weather. ❖ Jet Streams – WMO definition of Jet stream, different jet streams around the globe, Jet streams and weather ❖ Meso-scale meteorology, sea and land breezes, mountain/valley winds, mountain wave. ❖ Short range weather forecasting (Elementary ideas only); persistence, climatology and steering methods, movement and development of synoptic scale systems; Analogue techniques- prediction of individual weather elements, visibility, surface and upper level winds, convective phenomena.
    [Show full text]
  • Air Pressure and Wind
    Air Pressure We know that standard atmospheric pressure is 14.7 pounds per square inch. We also know that air pressure decreases as we rise in the atmosphere. 1013.25 mb = 101.325 kPa = 29.92 inches Hg = 14.7 pounds per in 2 = 760 mm of Hg = 34 feet of water Air pressure can simply be measured with a barometer by measuring how the level of a liquid changes due to different weather conditions. In order that we don't have columns of liquid many feet tall, it is best to use a column of mercury, a dense liquid. The aneroid barometer measures air pressure without the use of liquid by using a partially evacuated chamber. This bellows-like chamber responds to air pressure so it can be used to measure atmospheric pressure. Air pressure records: 1084 mb in Siberia (1968) 870 mb in a Pacific Typhoon An Ideal Ga s behaves in such a way that the relationship between pressure (P), temperature (T), and volume (V) are well characterized. The equation that relates the three variables, the Ideal Gas Law , is PV = nRT with n being the number of moles of gas, and R being a constant. If we keep the mass of the gas constant, then we can simplify the equation to (PV)/T = constant. That means that: For a constant P, T increases, V increases. For a constant V, T increases, P increases. For a constant T, P increases, V decreases. Since air is a gas, it responds to changes in temperature, elevation, and latitude (owing to a non-spherical Earth).
    [Show full text]
  • Lecture 4: Pressure and Wind
    LectureLecture 4:4: PressurePressure andand WindWind Pressure, Measurement, Distribution Forces Affect Wind Geostrophic Balance Winds in Upper Atmosphere Near-Surface Winds Hydrostatic Balance (why the sky isn’t falling!) Thermal Wind Balance ESS55 Prof. Jin-Yi Yu WindWind isis movingmoving air.air. ESS55 Prof. Jin-Yi Yu ForceForce thatthat DeterminesDetermines WindWind Pressure gradient force Coriolis force Friction Centrifugal force ESS55 Prof. Jin-Yi Yu ThermalThermal EnergyEnergy toto KineticKinetic EnergyEnergy Pole cold H (high pressure) pressure gradient force (low pressure) Eq warm L (on a horizontal surface) ESS55 Prof. Jin-Yi Yu GlobalGlobal AtmosphericAtmospheric CirculationCirculation ModelModel ESS55 Prof. Jin-Yi Yu Sea Level Pressure (July) ESS55 Prof. Jin-Yi Yu Sea Level Pressure (January) ESS55 Prof. Jin-Yi Yu MeasurementMeasurement ofof PressurePressure Aneroid barometer (left) and its workings (right) A barograph continually records air pressure through time ESS55 Prof. Jin-Yi Yu PressurePressure GradientGradient ForceForce (from Meteorology Today) PG = (pressure difference) / distance Pressure gradient force force goes from high pressure to low pressure. Closely spaced isobars on a weather map indicate steep pressure gradient. ESS55 Prof. Jin-Yi Yu ThermalThermal EnergyEnergy toto KineticKinetic EnergyEnergy Pole cold H (high pressure) pressure gradient force (low pressure) Eq warm L (on a horizontal surface) ESS55 Prof. Jin-Yi Yu Upper Troposphere (free atmosphere) e c n a l a b c i Surface h --Yi Yu p o r ESS55 t Prof. Jin s o e BalanceBalance ofof ForceForce inin thetheg HorizontalHorizontal ) geostrophic balance plus frictional force Weather & Climate (high pressure)pressure gradient force H (from (low pressure) L Can happen in the tropics where the Coriolis force is small.
    [Show full text]
  • Anticyclonic Atmospheric Circulation As an Analogue for the Warm and Dry Mid-Holocene Summer Climate in Central Scandinavia
    Clim. Past, 4, 215–224, 2008 www.clim-past.net/4/215/2008/ Climate © Author(s) 2008. This work is distributed under of the Past the Creative Commons Attribution 3.0 License. Anticyclonic atmospheric circulation as an analogue for the warm and dry mid-Holocene summer climate in central Scandinavia K. Antonsson1, D. Chen2, and H. Seppa¨3 1Department of Earth Sciences, Uppsala University, Villavagen¨ 16, 75236 Uppsala, Sweden 2University of Gothenburg, Box 460, 40530, Goteborg,¨ Sweden 3Department of Geology, P.O. Box 64, 00014, University of Helsinki, Helsinki, Finland Received: 26 March 2008 – Published in Clim. Past Discuss.: 16 May 2008 Revised: 1 September 2008 – Accepted: 12 September 2008 – Published: 21 October 2008 Abstract. Climate reconstructions from central Scandinavia 1 Introduction suggest that annual and summer temperatures were rising during the early Holocene and reached their maximum af- It is well established that atmospheric circulation plays an ter 8000 cal yr BP. The period with highest temperatures was important role in shaping the regional climate and influenc- characterized by increasingly low lake-levels and dry cli- ing the marked intra-seasonal climatic variability over Scan- mate, with driest and warmest conditions at about 7000 to dinavia (e.g. Busuioc et al., 1999; Chen, 2000; Slonosky 5000 cal yr BP. We compare the reconstructed climate pattern et al., 2000, 2001; Moberg and Jones, 2005; Achberger et with simulations of a climate model for the last 9000 years al., 2007). Scandinavian summer climate is highly vari- and show that the model, which is predominantly driven able. It is often characterized by rainy and cloudy weather by solar insolation patterns, suggests less prominent mid- with daily maximum temperatures well below 20◦C, but can Holocene dry and warm period in Scandinavia than the re- quickly switch into warm and dry weather, which sometimes constructions.
    [Show full text]
  • An Analysis of the Favorable Synoptic and Mesoscale Environments Associated with the January 22Nd 2017 Tornado Outbreak
    An Analysis of the Favorable Synoptic and Mesoscale Environments Associated with the January 22nd 2017 Tornado Outbreak Introduction The January 22nd 2017 tornado outbreak was the deadliest in South Georgia in nearly 17 years. From the pre-dawn hours through mid-afternoon, 4 significant (EF-2 or greater) tornadoes struck south Georgia, killing 16 people. While strong winds aloft, large height and pressure falls, and a warm, moist airmass were common across much of the Southeast, it appears that the favorable interplay between the synoptic environment and a well-defined, mesoscale boundary focused the strongest and longest-lived tornadoes in south Georgia. Forecast Overview Forecasters first noticed the potential for severe thunderstorms a week before the event, when some of the more reliable numerical weather prediction models (including the GFS and ECMWF) depicted an unusually strong low pressure system developing over the Southeast the following weekend. On January 16th, the Storm Prediction Center, the branch of the National Weather Service charged with forecasting severe thunderstorms across the continental U.S., placed much of the northeast Gulf Coast region in a “Slight Risk” of severe storms. (Figure 1). Figure 1. “Slight Risk” (15% probability) of severe storms, issued 6 days before tornado outbreak. On the evening of January 18th, the National Weather Service in Tallahassee posted a message on social media (Figure 2) outlining the forecast track of the upper- level disturbance which went on to produce the January 22nd outbreak. At this time the short wave trough was south of Alaska, over 4,000 miles northwest of Tallahassee, and still beyond the U.S.
    [Show full text]
  • PHAK Chapter 12 Weather Theory
    Chapter 12 Weather Theory Introduction Weather is an important factor that influences aircraft performance and flying safety. It is the state of the atmosphere at a given time and place with respect to variables, such as temperature (heat or cold), moisture (wetness or dryness), wind velocity (calm or storm), visibility (clearness or cloudiness), and barometric pressure (high or low). The term “weather” can also apply to adverse or destructive atmospheric conditions, such as high winds. This chapter explains basic weather theory and offers pilots background knowledge of weather principles. It is designed to help them gain a good understanding of how weather affects daily flying activities. Understanding the theories behind weather helps a pilot make sound weather decisions based on the reports and forecasts obtained from a Flight Service Station (FSS) weather specialist and other aviation weather services. Be it a local flight or a long cross-country flight, decisions based on weather can dramatically affect the safety of the flight. 12-1 Atmosphere The atmosphere is a blanket of air made up of a mixture of 1% gases that surrounds the Earth and reaches almost 350 miles from the surface of the Earth. This mixture is in constant motion. If the atmosphere were visible, it might look like 2211%% an ocean with swirls and eddies, rising and falling air, and Oxygen waves that travel for great distances. Life on Earth is supported by the atmosphere, solar energy, 77 and the planet’s magnetic fields. The atmosphere absorbs 88%% energy from the sun, recycles water and other chemicals, and Nitrogen works with the electrical and magnetic forces to provide a moderate climate.
    [Show full text]
  • Lecture 1 UK Weather Lecture 5 UK Weather Is Dominated by The
    Lecture 5 Lecture 1 UK weather UK weather is dominated by the passage of low pressure systems (= extratropical cyclones = depressions). The study of mid-latitude weather systems began in earnest when it became possible to take synoptic weather observations. Admiral Robert Fitzroy (1805 - 1865) 1 5.1 The Norwegian cyclone model …a theory explaining the life- cycle of an extra-tropical storm. Idealized life cycle of an extratropical cyclone (2 - 8 days) (a) (b) (c) (d) (e) (f) 2 3 Where do extratropical cyclones form? Hoskins and Hodges (2002) 5.2 Upper-air support Surface winds converge in a low pressure centre and diverge in a high pressure ⇒ must be vertical motion In the upper atmosphere the flow is in geostrophic balance, so there is no friction forcing convergence/divergence. ∴ if an upper level low and surface low are vertically stacked, the surface convergence will cause the low to fill and the system to dissipate. 4 Weather systems tilt westward with height, so that there is a region of upper-level divergence above the surface low, and upper-level convergence above the surface high. 700mb height Downstream of troughs, divergence leads to favorable locations for ascent (red/orange), while upstream of troughs convergence leads to favorable conditions for descent (purple/blue). 5 When upper-level divergence is stronger than surface convergence, surface pressures drop and the low intensifies. When upper-level divergence is less than surface convergence, surface pressures rise and the low weakens. Waves in the upper level flow Typically 3-6 troughs and ridges around the globe - these are known as planetary waves or Rossby waves Instantaneous snapshot of 300mb height (contours) and windspeed (colours) 6 Right now….
    [Show full text]