Jump to content
Holidays
Local
Radar
Snow?
  • Welcome to the new Netweather community learning and research area. We've only just started in here, so keep checking back for new articles and guides. And please let the team know if there's something you'd like to see covered.

  • Sign in to follow this  

    Contrails, what are they?


    johnholmes

    What are contrails?

    They are the white trails from aircraft exhausts at the rear of the engine. They add to the local humidity of the air the aircraft is flying through which tends to super saturate the air. As the gases coming from the engine are high this helps to raise the temperature of the surrounding air, thus the air can hold more water vapour(yes it really does for the doubters!), before it becomes saturated. There are actually two opposing forces at work. (1) the water vapour in the exhaust trying to saturate the air, and (2) the hot gases of the exhaust trying to decrease the relative humidity. When an exact balance is created between the outside air temperature and the local humidity then condensation trails will occur. Called CONTRAILS and coded in meteorology as COTRA(COndensation TRAils)

    The trails may last very briefly or for quite long periods. They can have dimensions of several kilometres across and several hundred metres in depth. They spread because there is turbulence due to the aircraft moving through the air, and differences in wind speed along the path of the aircraft. Some believe there may be some input from solar heating. If they last a long time then they can tend to mask or at least decrease the sunshine striking the ground adjacent to the trails.

    Forecasters can use upper air diagrams to predict when and where they will occur. This technique was developed during the second World War when being seen was not something enemy aircraft wanted.

    As a forecast guide the following is what is used. I am unable to reproduce a t-phi diagram which has it plotted. If the actual airmass temperature is below these values at the heights given then contrails can occur.

    -24C at around sea level, in a linear line to -45C at 50,000ft. This is called the MINTRA line (MINimum TRAil line)

    So on the skew-t for Watnall (Nottingham) below for 12z today, there could be contrails, assuming its moist enough, above about 24-25,000ft.

    post-847-1193778611_thumb.jpg

    Unfortunately the satellite photographs from this afternoon do not show this very clearly. There are some but not good enough for teaching purposes, so I’ll wait until the two coincide.

    John Holmes

    Sign in to follow this  


    User Feedback

    Recommended Comments

    There are no comments to display.



    Guest
    Add a comment...

    ×   Pasted as rich text.   Restore formatting

      Only 75 emoji are allowed.

    ×   Your link has been automatically embedded.   Display as a link instead

    ×   Your previous content has been restored.   Clear editor

    ×   You cannot paste images directly. Upload or insert images from URL.


  • Useful links to basic information and learning material

    For those wishing to learn the basics about weather, climate and meteorology, this page provides links to the wealth of impartial information and learning material available from a number of national meteorological organisations. Learning about Weather (UK Met Office) https://www.metoffice.gov.uk/weather/learn-about/weather NOAA National Weather Service (USA) A huge source of material: https://www.weather.gov/jetstream/matrix Bureau of Meteorology (Australia) A comprehensive A

    Blessed Weather
    Blessed Weather
    The Basics

    Rapid Cyclogenesis

    Here are the current Papers & Articles under the research topic Rapid Cyclogenesis. Click on the title of a paper you are interested in to go straight to the full paper. Papers and articles covering the basics (ideal for learning) are shown in Green. Rapid Cyclogenesis (excellent source of explanatory info and illustrative diagrams and satellite images) A Composite Study of Explosive Cyclogenesis in Different Sectors of the North Atlantic. Part I: Cyclone Structure and Evolution

    Blessed Weather
    Blessed Weather
    Research

    Thunderstorms

    Here are the current Papers & Articles under the research topic Thunderstorms. Click on the title of a paper you are interested in to go straight to the full paper. A climatology of convective available potential energy in Great Britain A lightning climatology for Europe and the UK, 1990–99 Mesoscale convective systems over the UK, 1981-97 Types of Thunderstorms The Met Office Arrival Time Difference (ATD) system for thunderstorm detection and lightning location.

    Blessed Weather
    Blessed Weather
    Research

    What are Noctilucent Clouds?

    Noctilucent clouds are visible in June but rare enough to cause excitement. These high ice crystal clouds can only be seen in the midsummer twilight. Once the sun comes out the light is too strong for these delicate, pale threads to be seen, they need the semi-darkness. Usually, cloud viewed in high latitudes, they were seen in mid-June 2018 in Norfolk and the Netherlands with brilliant displays over northern Britan and Northern Ireland.  Read the full article here: https://www.netweather.t

    Paul
    Paul
    The Basics 1

    What is the polar vortex?

    The Polar Vortex is a wind pattern that circles over the polar regions of both the northern hemisphere and southern Hemisphere, looping west to east. Much of the cold circulation of the PV is contained within the upper atmosphere over the polar regions. Read the full article here: https://www.netweather.tv/weather-forecasts/news/6291-what-is-the-polar-vortex

    Paul
    Paul
    The Basics

    Wintry showers and what counts for White Christmas observations?

    You may have thought that snow meant snow. We know from the train companies there can be the wrong type of snow and in other languages, there is a wide variety of descriptions for snow forms. It seems within the betting world what counts for a White Christmas is also quite varied.  Frozen Precipitation - that's what it is all about... Read the full article here: https://www.netweather.tv/weather-forecasts/news/8573-wintry-showers-and-what-counts-for-white-christmas-observations  

    Paul
    Paul
    The Basics
×
×
  • Create New...