DOCSLIB.ORG

Chapter 7 Precipitation Processes

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Chapter 7 Precipitation Processes Chapter 7 Precipitation Processes Chapter overview: • Supersaturation and water availability • Nucleation of liquid droplets and ice crystals • Liquid droplet and ice growth by diffusion • Collision and collection • Precipitation Formation • Precipitation types o Rain o Snow o Sleet and freezing rain o Hail Hydrometeors: Liquid and ice particles that form in the atmosphere Precipitation: Occurs when hydrometeors become large enough to fall to the Earth’s surface How does precipitation form? Why do some clouds produce precipitation while other clouds do not? How does a cloud droplet grow to become raindrop? These are the questions we will address in this chapter. The volume of a typical cloud droplet is one millionth the volume of a typical raindrop. Supersaturation and Water Availability Supersaturation: A condition in which there is more water vapor in the air than it can hold at equilibrium. How will the vapor pressure (e) compare to the saturation vapor pressure (es) when the air is supersaturated? What is the value of the relative humidity (RH) when the atmosphere is supersaturated? The supersaturation fraction (S) or supersaturation percentage (S%) is defined as: S = RH - 1 or S% = 100% x S = RH% - 100% The supersaturation fraction can also be found from the vapor pressure and saturation vapor pressure: e r S = −1 or S ≈ −1 es rs How does the mixing ratio (r) and saturation mixing ratio (rs), and total water mixing ratio (rT) change as an initially unsaturated air parcel is lifted to and above its LCL? The excess water mixing ratio (rE) is defined as: rE = rT - rs The excess water will increase above the LCL, as shown to the left. This excess water will condense onto liquid drops or deposit onto ice crystals such that: rE = rL + ri Why would the observed rE differ from the adiabatic value of rE? Note: Liquid cloud droplets can exist as supercooled water at temperatures between 0 and -40 deg C. The available supersaturation (SA) for cloud droplet and ice crystal growth is: rE rT SA = = −1 rs rs As hydrometeors form and grow above the LCL how will the mixing ratio (r), total water mixing ratio (rT), supersaturation (S), and available supersaturation (SA) change? Nucleation of Liquid Droplets Nucleation: The creation of new droplets In the atmosphere nucleation occurs on tiny dust particles (called cloud condensation nuclei) in a process called heterogeneous nucleation. Aerosol: Any tiny solid or liquid particle suspended in the air. Cloud condensation nuclei (CCN): A subset of aerosol particles that can nucleate cloud droplets. What properties must an aerosol have in order to serve as a CCN? How does the number of condensation nuclei differ in air over land or the ocean? What impact does this have on the number and size of cloud droplets that form in a cloud over land or over the ocean? At typical excess water mixing ratios and CCN numbers found in the atmosphere cloud droplets will usually have radii of 2 to 50 µm. These cloud droplets are small enough that even a slight updraft can keep them suspended. The textbook discusses the details of how water vapor condenses onto CCN and how these droplets can grow from haze to cloud droplet sized particles, but we will not discuss these details in class. Nucleation of Ice Crystals Why can cloud droplets exist in the liquid phase even when the temperature is below 0°C? What causes supercooled cloud droplets to freeze? Nucleation of ice crystals can occur by either homogenous or heterogeneous freezing. Homogenous freezing nucleation: The spontaneous freezing of supercooled liquid water droplets as temperature decreases to near -40 deg C. Below what temperature do all cloud droplets freeze? Heterogeneous freezing nucleation: The freezing of supercooled liquid water in the presence of a small dust particle (called an ice nucleus). There are three possible heterogeneous freezing mechanisms. Deposition nucleation: Water vapor is deposited (as ice) directly on a deposition nucleus. Immersion freezing: A freezing nucleus within a supercooled liquid droplet will cause the liquid to freeze when the droplet is cooled below a critical temperature that depends on the type of ice nucleus. Contact freezing: A supercooled droplet, with no embedded ice nuclei, freezes when an external ice nucleus comes in contact with the droplet. Only particles with a molecular structure that is similar to ice can serve as ice nuclei. What type of particles act as ice nuclei in the atmosphere? How does the number of ice nuclei and cloud condensation nuclei compare? The shape of ice crystal that forms from deposition varies depending on the temperature and the supersaturation (or vapor density excess) as shown to the left. As these ice particles fall through a cloud they will encounter different temperatures and supersaturations and can acquire more complex shapes. Liquid Droplet Growth by Diffusion In a supersaturated environment water vapor will diffuse towards a cloud droplet causing the cloud droplet to grow. The rate of water vapor diffusion depends on the supersaturation (or mixing ratio) gradient. Based on the figure above will the small or large droplet grow more quickly by diffusion of water vapor? Due to differences in droplet growth by diffusion for different sized droplets a cloud that contained only droplets growing by diffusion would have nearly all the same size cloud droplets (monodisperse). Ice Crystal Growth by Diffusion Cold cloud: A cloud in which the temperature is below freezing at some locations in the cloud and cloud droplets may be either liquid or ice. How does the equilibrium vapor pressure differ over a liquid cloud droplet and an ice crystal? The saturation vapor pressure over a water surface is greater than the saturation vapor pressure over an ice surface. What impact does the difference in saturation vapor pressure over water and ice have on evaporation or condensation occurring over cloud droplets and ice crystals? The process of ice crystals growing at the expense of cloud droplets is called the Wegener - Bergeron - Findeisen (WBF) process (or cold cloud process). At what temperature is the WBF process at a maximum? Collision and Collection Terminal velocity: The maximum fall speed of an object that occurs when gravity is balanced by frictional drag. How does the fall speed of hydrometeor change as its size increases? In a cloud with many different sized hydrometeors the different fall speeds will result in hydrometeors colliding with each other. We need to consider collisions between: - just cloud droplets - just ice crystals - a mixture of ice crystals and cloud droplets Coalescence: The merging of two liquid cloud droplets. Warm cloud: A cloud in which the temperature is above freezing everywhere and all cloud droplets are liquid. Collision and coalescence is the only way that cloud droplets can grow to raindrop size in a warm cloud. Aggregation: The process in which ice particles collide and stick together. Aggregation is favored for dendrite shaped ice crystals and when the temperature of the ice is warmer than -5 deg C. Accretion (riming): The growth of ice crystals by collision, collection, and instant freezing of supercooled liquid droplets. Graupel: A hydrometeor that has become so heavily rimed that the shape (habit) of the original ice crystal is completely covered. Precipitation Formation Warm Clouds What factors enhance the collision and coalescence process in a warm cloud? • A range of cloud droplet sizes • The cloud’s liquid water content • Cloud thickness • Updraft • Electric charge of droplets and electric field in the cloud What factors create a broad distribution of cloud droplet sizes? Which type of cloud would you expect to produce larger raindrops - a thin, warm stratus cloud with a weak updraft or a warm, cumulus cloud with a moderate updraft? Cold Clouds The WBF process allows the small number of ice crystals to grow into larger ice particles in cold clouds with supercooled water. These large, falling ice crystals can then grow further through aggregation and riming. Does this frozen precipitation (graupel or snowflakes) always reach the ground in a frozen state? For both warm and cold clouds the thicker the cloud is the larger the size of raindrops produced and the heavier the precipitation rate. Precipitation Types Rain Rain: Falling drop of liquid water with a diameter greater than 0.5 mm Drizzle: Falling drop of liquid water with a diameter less than 0.5 mm Virga: Falling precipitation that evaporates before reaching the ground Snow Snow: Falling ice crystals or snowflakes. Blizzard: Low visibility (less than or equal to 0.25 miles) due to falling or blowing snow with wind speeds greater or equal to 35 mph for at least 3 hours. Sleet and Freezing Rain Sleet: A raindrop that has frozen before reaching the ground. What atmospheric conditions lead to the formation of sleet? Freezing rain: Rain that freezes upon striking a solid object, such as the ground. What is the difference between sleet and freezing rain? Rime: Small supercooled fog or cloud droplets that freeze as white or milky granular ice upon striking an object whose temperature is below 0°C. Ice storm: A storm in which there is a substantial accumulation of freezing rain. What difference in atmospheric conditions lead to the formation of rain, freezing rain, sleet, or snow? Hail Hail: Pieces of ice, that are either transparent or partially opaque, ranging in size from that of small peas to that of golf balls or larger. How does hail form? What causes hail to eventually fall to the ground? How does hail differ from graupel? Precipitation Distribution .
Load more

Recommended publications
  • METAR/SPECI Reporting Changes for Snow Pellets (GS) and Hail (GR)
    U.S. DEPARTMENT OF TRANSPORTATION N JO 7900.11 NOTICE FEDERAL AVIATION ADMINISTRATION Effective Date: Air Traffic Organization Policy September 1, 2018 Cancellation Date: September 1, 2019 SUBJ: METAR/SPECI Reporting Changes for Snow Pellets (GS) and Hail (GR) 1. Purpose of this Notice. This Notice coincides with a revision to the Federal Meteorological Handbook (FMH-1) that was effective on November 30, 2017. The Office of the Federal Coordinator for Meteorological Services and Supporting Research (OFCM) approved the changes to the reporting requirements of small hail and snow pellets in weather observations (METAR/SPECI) to assist commercial operators in deicing operations. 2. Audience. This order applies to all FAA and FAA-contract weather observers, Limited Aviation Weather Reporting Stations (LAWRS) personnel, and Non-Federal Observation (NF- OBS) Program personnel. 3. Where can I Find This Notice? This order is available on the FAA Web site at http://faa.gov/air_traffic/publications and http://employees.faa.gov/tools_resources/orders_notices/. 4. Cancellation. This notice will be cancelled with the publication of the next available change to FAA Order 7900.5D. 5. Procedures/Responsibilities/Action. This Notice amends the following paragraphs and tables in FAA Order 7900.5. Table 3-2: Remarks Section of Observation Remarks Section of Observation Element Paragraph Brief Description METAR SPECI Volcanic eruptions must be reported whenever first noted. Pre-eruption activity must not be reported. (Use Volcanic Eruptions 14.20 X X PIREPs to report pre-eruption activity.) Encode volcanic eruptions as described in Chapter 14. Distribution: Electronic 1 Initiated By: AJT-2 09/01/2018 N JO 7900.11 Remarks Section of Observation Element Paragraph Brief Description METAR SPECI Whenever tornadoes, funnel clouds, or waterspouts begin, are in progress, end, or disappear from sight, the event should be described directly after the "RMK" element.
    [Show full text]
  • ESSENTIALS of METEOROLOGY (7Th Ed.) GLOSSARY
    ESSENTIALS OF METEOROLOGY (7th ed.) GLOSSARY Chapter 1 Aerosols Tiny suspended solid particles (dust, smoke, etc.) or liquid droplets that enter the atmosphere from either natural or human (anthropogenic) sources, such as the burning of fossil fuels. Sulfur-containing fossil fuels, such as coal, produce sulfate aerosols. Air density The ratio of the mass of a substance to the volume occupied by it. Air density is usually expressed as g/cm3 or kg/m3. Also See Density. Air pressure The pressure exerted by the mass of air above a given point, usually expressed in millibars (mb), inches of (atmospheric mercury (Hg) or in hectopascals (hPa). pressure) Atmosphere The envelope of gases that surround a planet and are held to it by the planet's gravitational attraction. The earth's atmosphere is mainly nitrogen and oxygen. Carbon dioxide (CO2) A colorless, odorless gas whose concentration is about 0.039 percent (390 ppm) in a volume of air near sea level. It is a selective absorber of infrared radiation and, consequently, it is important in the earth's atmospheric greenhouse effect. Solid CO2 is called dry ice. Climate The accumulation of daily and seasonal weather events over a long period of time. Front The transition zone between two distinct air masses. Hurricane A tropical cyclone having winds in excess of 64 knots (74 mi/hr). Ionosphere An electrified region of the upper atmosphere where fairly large concentrations of ions and free electrons exist. Lapse rate The rate at which an atmospheric variable (usually temperature) decreases with height. (See Environmental lapse rate.) Mesosphere The atmospheric layer between the stratosphere and the thermosphere.
    [Show full text]
  • The Distribution of Aircraft Icing Accretion in China—Preliminary Study
    atmosphere Article The Distribution of Aircraft Icing Accretion in China—Preliminary Study Jinhu Wang 1,2,3,4,* , Binze Xie 1,* and Jiahan Cai 1 1 Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Key Laboratory for Aerosol-Cloud-Precipitation of China Meteorological Administration, Nanjing University of Information Science and Technology (NUIST), Nanjing 210044, China; [email protected] 2 Key Laboratory of Middle Atmosphere and Global Environment Observation, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China 3 National Demonstration Center for Experimental Atmospheric Science and Environmental Meteorology Education, Nanjing University of Information Science and Technology, Nanjing 210044, China 4 Nanjing Xinda Institute of Safety and Emergency Management, Nanjing 210044, China * Correspondence: [email protected] (J.W.); [email protected] (B.X.); Tel.: +86-138-1451-2847 (J.W.) Received: 10 June 2020; Accepted: 11 August 2020; Published: 18 August 2020 Abstract: The icing environment is an important threat to aircraft flight safety. In this work, the icing index is calculated using linear interpolation and based on temperature and relative humidity (RH) curves obtained from radiosonde observations in China. The results show that: (1) there are obvious differences in icing index distribution in parameter over various climatic regions of China. The differences are reflected in duration, main altitude, and ice intensity. The reason for the differences is related to the temperature and humidity environment. (2) Before and after the summer rainfall process, there are obvious changes in the ice accretion index in the 4–6 km altitude area of Northeast China, and the areas with serious ice accretion are coincident with areas with large rainfall estimates.
    [Show full text]
  • Kinds of Clouds
    JJoosseelllleMM aaeYY .MM aanniittii MMrrss.SS hhaarroonDD aavviidd IIV–DD eJJ eessuu ss SScciieennccee Kinds of Clouds Cumulus clouds are white, puffy clouds that look like pieces of floating cotton. u!ulus clouds are often called "fair#weather clouds". $he %ase of each cloud is flat and the top of each cloud has rounded towers. &hen the top of the cu!ulus clouds rese!%le the head of a cauliflower, it is called cu!ulus congestus or towering cu!ulus. $hese clouds grow upward and they can develop into giant cu!uloni!%us clouds, which are thunderstor! clouds. 'n arcus cloud is a low, hori(ontal cloud for!ation. )oll clouds and shelf clouds are the two types of arcus clouds. ' shelf cloud is usually associated with the leading edge of thunderstor! outflow* roll clouds are usually for!ed %y outflows of cold air fro! sea %ree(es or cold fronts in the a%sence of thunderstor!s. Stratus clouds are unifor! grayish clouds that often cover the entire sky. $hey rese!%le fog that doesn+t reach the ground. ight !ist or dri((le so!eti!es falls out of these clouds. '' nimbus cloud is a cloud that produces precipitation. -sually the precipitation reaches the ground as rain,, hail,, snow, or sleet.. alling precipitation !ay evaporate as virga. )ain co!es out of ni!%us clouds and this is called precipitation. Since ni!%us clouds are dense with water, they appear darker than other clouds. /i!%us clouds are for!ed at low altitudes and are typically spread unifor!ly across the sky.
    [Show full text]
  • Popular Summary
    POPULAR SUMMARY Ice-Crystal Fallstreaks from Supercooled Liquid Water Parent Clouds James R. Campbell Science Systems & Applications, Inc., Greenbelt, Maryland David OK. Starr, Ellsworth J. Welton, James D. Spinhirne NASA Goddard Space Flight Center, Greenbelt, MD Richard A. Ferrare NASA Langley Research Center, Hampton, VA Submitted to Monthly Weather Review September 2003 On 3 1 December 2001, ice-crystal fallstreaks (e.g., cirrus uncinus, or colloquially "Mare's Tails") from supercooled liquid water parent clouds were observed by ground-based lidars pointed vertically fi-om the Atmospheric Radiation Measurement Southern Great Plains (SGP) facility near Lamont, Oklahoma. The incidence of liquid phase cloud with apparent ice-phase precipitation is investigated. Scenarios for mixed-phase particie nucleation, and fallstreak formation and sustenance are discussed. The observations are unique in the context of the historical reverence given to the commonly observed cirrus uncinus fallstreak (wholly ice) versus this seemingly contradictory coincidence of liquid water begetting ice-crystal streaks. In contrast to the more common observations of glaciation of liquid phase altocumulus or altostratus clouds leading to erosion of the parent cloud and development of a cloud "hole" and persistent ice fallstreak below it, we find that the liquid-phase parent cloud persists in this case, a finding more common in the arctic than in middle latitudes as here. Ice-Crystal Fallstreaks from Supercooled Liquid Water Parent Clouds James R Campbell* Science Systems & Applications, Inc., Greenbelt, Maiyland David O’C. Starr, Ellsworth J. Welton, James D. Spinhirne NASA Goddard Space Flight Center, Greenbelt, MD Richard A. Ferrare NASA Langley Research Center, Hampton, VA Submitted to Monthly Weather Review * Corresponding author address: 10210 Greenbelt Rd, Suite 600, Lanham, MD, USA, 20706.
    [Show full text]
  • Observation and Analysis of Meteorological Conditions for Icing of Wires in Guizhou, China
    Journal of Geoscience and Environment Protection, 2019, 7, 214-230 https://www.scirp.org/journal/gep ISSN Online: 2327-4344 ISSN Print: 2327-4336 Observation and Analysis of Meteorological Conditions for Icing of Wires in Guizhou, China Jifen Wen1, Ran Jia2, Yuxiang Peng1* 1Guizhou Provincial Office of Weather Modification, Guiyang, China 2Key Laboratory of Atmospheric Physics and Atmospheric Environment, Nanjing University of Information Science & Technology, Nanjing, China How to cite this paper: Wen, J. F., Jia, R., Abstract & Peng, Y. X. (2019). Observation and Analysis of Meteorological Conditions for Icing of wires is a product of rain, fog, and freezing rain, and is a common Icing of Wires in Guizhou, China. Journal meteorological disaster in winter in Guizhou Province of China. It is ex- of Geoscience and Environment Protection, tremely harmful to facilities such as power transmission and communication 7, 214-230. https://doi.org/10.4236/gep.2019.79015 lines, and has caused huge economic loss up to 48.9566 billion dollars a year. Based on the meteorological records of Guizhou from 1967, we analyze the Received: January 4, 2019 meteorological characteristics during the icing of wires, and obtain the tem- Accepted: September 24, 2019 perature, wind speed and direction conditions of the ice accident. The icing of Published: September 27, 2019 wires is carried out by supercooling raindrops, freezing of the clouds, freezing Copyright © 2019 by author(s) and and spreading on the wires. Different types of supercooled raindrops and Scientific Research Publishing Inc. cloud freezing and freezing processes will form different types of ice accre- This work is licensed under the Creative Commons Attribution International tion; wind direction and wind speed will affect the growth of ice accretion by License (CC BY 4.0).
    [Show full text]
  • Classification of Clouds Clouds Are Usually Classified According to Their Height and Appearance
    CLOUDS Clouds are condensed droplets of water and ice crystals. The nuclei of those droplets are dust particles. Near the surface these drops form fog and in the free atmosphere, they form clouds. Clouds have been defined as visible aggregation of minute water droplets and / or ice particles in the air, usually above the general ground level. Air contains moisture and this is extremely important to the formation of clouds. Clouds are formed around microscopic particles such as dust, smoke, salt crystals & other materials that are present in the atmosphere. These materials are called Cloud Condensation Nucleus (CCN). Without these, no cloud formation will take place. There are certain special types, known as ice nucleus, on which droplets freeze or ice crystals form directly from water vapour. Generally condensation nuclei are present in plenty in air. But there is scarcity of special ice forming nuclei. Generally clouds are made up of billion of these tiny water droplets or ice crystals or combination of both. When a current of air rises upwards due to increased temperature it goes up, expands and gets cooled. If the cooling continues till the saturation point is reached, the water vapour condenses and forms clouds. The condensation takes place on a nucleus of dust particles. The water particles individually are very small and suspended in the air. Only when the droplets coalesce to from a drop of sufficient weight, to overcome the resistance of air, they fall as rain. Clouds are considered essential and accurate tools for weather forecasting. Classification of clouds Clouds are usually classified according to their height and appearance.
    [Show full text]
  • Metar Abbreviations Metar/Taf List of Abbreviations and Acronyms
    METAR ABBREVIATIONS http://www.alaska.faa.gov/fai/afss/metar%20taf/metcont.htm METAR/TAF LIST OF ABBREVIATIONS AND ACRONYMS $ maintenance check indicator - light intensity indicator that visual range data follows; separator between + heavy intensity / temperature and dew point data. ACFT ACC altocumulus castellanus aircraft mishap MSHP ACSL altocumulus standing lenticular cloud AO1 automated station without precipitation discriminator AO2 automated station with precipitation discriminator ALP airport location point APCH approach APRNT apparent APRX approximately ATCT airport traffic control tower AUTO fully automated report B began BC patches BKN broken BL blowing BR mist C center (with reference to runway designation) CA cloud-air lightning CB cumulonimbus cloud CBMAM cumulonimbus mammatus cloud CC cloud-cloud lightning CCSL cirrocumulus standing lenticular cloud cd candela CG cloud-ground lightning CHI cloud-height indicator CHINO sky condition at secondary location not available CIG ceiling CLR clear CONS continuous COR correction to a previously disseminated observation DOC Department of Commerce DOD Department of Defense DOT Department of Transportation DR low drifting DS duststorm DSIPTG dissipating DSNT distant DU widespread dust DVR dispatch visual range DZ drizzle E east, ended, estimated ceiling (SAO) FAA Federal Aviation Administration FC funnel cloud FEW few clouds FG fog FIBI filed but impracticable to transmit FIRST first observation after a break in coverage at manual station Federal Meteorological Handbook No.1, Surface
    [Show full text]
  • Cloud Seeding Natural Cloud Seeding
    Ice crystals grow at expense of water droplets and fall. Cloud Seeding • Necessary ingredient: Presence of supercooled clouds • Silver iodide (AgI) serves as ice Dry-ice-seeded racetrack pattern in supercooled cloud layer nuclei for the ice-crystal process (top temperature at 750 km & -5.6°C ) 30 min after the seeding. Utica, NY, 24 Nov 1948 (Langmuir 1961). (deposition from water droplets) to take place and initiate precipitation. • Effectiveness is uncertain. 300 km Seeding track over central China on 0735 UTC 14 Mar 2000 as observed by NOAA-14 AVHRR . Natural Cloud Seeding Cold enough for ice crystal formation Æ On the lee, precipitation may be observed in separate bands 1 SO2, CO2 Cloud seeding experiment on the global scale by human-induced Acid rain Global warming increase in aerosols (condensation Aerosols nuclei and ice nuclei). Æ Increased number of cloud droplets Æ clouds become brighter. ÆIncreased number of raindrops decrease their size Æ decreased surface rainfall and clouds persist longer. Æ Both effects help cool the earth by reflecting sun light. Aerial view shows Amazon forest burning in Mato Grosso state, Brazil, August 9, 2005. Precipitation Types Rain over Roi Et, Thailand 2 Virga Rain or snow that evaporates before reaching the surface. Cirrus as Virga Falling ice crystals that evaporate in air. 3 Mammatus Clouds Downward motion in convection caused by weight of falling precipitation and cooling by evaporating precipitation. Precipitation Types Precipitation reaching the surface can take on different forms depending on the vertical temperature profile. Sleet is solid before it reaches the ground. Freezing rain is liquid (super cooled) until it strikes.
    [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]
  • (METAR) the Aviation Routine Weather Report
    December 1999 Section 2 AVIATION ROUTINE WEATHER REPORT (METAR) The aviation routine weather report (METAR) is the weather observer’s interpretation of the weather conditions at a given site and time. The METAR is used by the aviation community and the National Weather Service (NWS) to determine the flying category - visual fight rules (VFR), marginal VFR (MVFR), or instrument flight rules (IFR) - of the airport, as well as produce the Aviation Terminal Forecast (TAF). (See Section 4.) Although the METAR code is being adopted worldwide, each country is allowed to make modifications or exceptions to the code for use in that particular country. The U.S.A. reports temperature and dew point in degrees Celsius and continues to use current units of measurement for the remainder of the report. The elements in the body of a METAR report are separated with a space. The only exception is temperature and dew point that are separated with a solidus (/). When an element does not occur, or cannot be observed, the preceding space and that element are omitted from that particular report. A METAR report contains the following elements in order as presented: 1. Type of report 2. ICAO station identifier 3. Date and time of report 4. Modifier (as required) 5. Wind 6. Visibility 7. Runway visual range (RVR) (as required) 8. Weather phenomena 9. Sky condition 10. Temperature/dew point group 11. Altimeter 12. Remarks (RMK) (as required) The following paragraphs describe the elements in a METAR report. A sample report will accompany each element with the subject element highlighted. TYPE OF REPORT METAR KLAX 140651Z AUTO 00000KT 1SM R35L/4500V6000FT -RA BR BKN030 10/10 A2990 RMK AO2 There are two types of reports: The METAR and the aviation selected special weather report (SPECI).
    [Show full text]
  • Meteorological Conditions of Ice Accretion Based on Real-Time Observation of High Voltage Transmission Line
    Article Atmospheric Science March 2012 Vol.57 No.7: 812818 doi: 10.1007/s11434-011-4868-2 SPECIAL TOPICS: Meteorological conditions of ice accretion based on real-time observation of high voltage transmission line ZHOU Yue, NIU ShengJie*, LÜ JingJing & ZHAO LiJuan Key Laboratory of Meteorological Disaster of Ministry of Education, School of Atmospheric Physics, Nanjing University of Information Science & Technology, Nanjing 210044, China Received May 3, 2011; accepted September 27, 2011; published online November 26, 2011 Meteorological conditions during ice accretion on the 500 kV high voltage transmission lines and test cables are presented, to- gether with a calculation of liquid water content (LWC). The data include meteorological observations and real-time ice accretion on the transmission lines of the central China power grid, from 2008 to 2009 in Hubei Province. Also included are observations of ice thickness, microphysics of fog droplets, and other relevant data from a nearby automated weather station at Enshi radar station, from January to March 2009. Results show that temperature at Zhangen tower #307 was correlated with the temperature at Enshi radar station. The temperature on the surface of the high voltage transmission line was 2–4°C higher than ambient air temperature, although the temperatures were positively correlated. Ice formation temperature was about −2°C and ice shedding temperature was about −2 to −1°C on the high voltage transmission line, both of which were lower than the temperature threshold values on the test cable. Ice thickness was significantly affected by temperature variation when the ice was thin. The calculated LWC was correlated with observed LWC, although the calculated value was greater.
    [Show full text]