Jun 5, 2023
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Foehn Winds
Foehn winds are warm, dry winds that sometimes flow down the lee side of mountains ranges. Two well known examples of Foehn winds are the Chinook in the Canadian Rockies and the Santa Ana in California. Chinook roughly translates to ‘snow eater’, named for their ability to melt accumulated snow. Often occurring in the late fall and winter months, these winds can dramatically affect weather hundreds of kilometers away from the mountain range due to the strong winds and large, rapid temperature increases. In 1972 a Chinook wind caused an incredible temperature increase of 57°C (from -48 to 9°C) in Loma, Montana - the largest temperature change ever recorded over a 24-hour period.
Foehn winds occur because of the adiabatic heating and cooling of the air as it travels up and over the a mountain range. The adiabatic lapse rate is the rate at which the temperature of a parcel of air changes as it ascends or descends, varying depending on its moisture content. The average adiabatic lapse rate of unsaturated air (dry adiabatic lapse rate) is 3°C /1,000ft, and the average adiabatic lapse rate of saturated air (moist adiabatic lapse rate) is 1.5°C /1000 ft. The difference between the dry and moist adiabatic lapse rates is due to the latent heat of condensation. When air becomes saturated and excess water vapour begins to condense to form clouds, heat is released, decreasing the adiabatic lapse rate.
When unsaturated air is forced upwards by a mountain range it expands and beings cooling at the dry adiabatic lapse rate. If rising continues the air will eventually reach its dew point and become saturated, where the air can not hold any more water vapour and the excess will condense and form clouds. This elevation is called the lifting condensation level. Most of the condensed moisture will fall as rain. As the saturated air continues to ascend the range it will cool more slowly, at the moist adiabatic lapse rate. When the air reaches the peak of the mountain range and begins descending on the lee side it warms by adiabatic compression. The air is now unsaturated because some of the moisture has been removed, so it warms at the dry adiabatic lapse rate. This creates areas, where at the same elevation, the air on the lee side of the mountain is much warmer than the air on the windward side.
Here’s a simplified example of how a Foehn wind warms as it passes over a 5000ft mountain range. Let’s say that the air temperature is 20°C at sea level on the windward side of the mountain range and that it will reach its dew point at 14°C or 2000ft. For the first 2000ft that the air must ascend the mountain range, it cools at the dry adiabatic lapse rate (3°C/1000ft) to 14°C. For the last 3000ft (from 2000ft to 5000ft), the air is saturated and excess moisture from the rising air condenses into a cloud and it rains. This saturated air cools at the moist adiabatic lapse rate (1.5°C/1000ft) as it rises, further decreasing its temperature by 4.5°C. This means that the air temperature at the top of the mountain range is 9.5°C. This air now descends the 5000ft lee slope of the mountain where it is compressed and warms at the dry adiabatic lapse rate, increasing the sea level temperature by 15°C to 24.5°C. By the process of adiabatic cooling and heating over the mountain range, the temperature of the air has increased by 4.5°C.
CD
Sources https://www.skybrary.aero/index.php/Lapse_Rate https://bit.ly/2MduL4Q https://www.metoffice.gov.uk/learning/wind/foehn-effect https://bit.ly/2Mvtd2J https://bit.ly/2KETuu3
Image Sources Richard Masoner https://bit.ly/2nqMl7m https://bit.ly/2vW3WYw (Modified)
Clearing
Low clouds over the ocean are important for regulating the Earth’s climate as they reflect a lot of solar energy back into space. The dynamics of these clouds are important to understand the planet’s weather and also to understand the shallow ecosystems in the ocean. This video shows something funny happening to these clouds in the southern ocean off the west coast of Africa – they’re literally knocked out of existence by a wave.
Scientists led by a group at NC State collected a number of satellite views of these clouds off the African coast and found that there’s a particular season and time of day where the clouds are just knocked away. The clouds are hit by a gravity wave – a wave in the atmosphere where Gravity is the restoring force (note that this is different from a gravitational wave: https://tmblr.co/Zyv2Js21a6wKe).
Heating during the day over Africa during one specific time of year triggers this gravity wave. The wave migrates as part of a chain heading out to the ocean, and in the process it hits these clouds. Sometimes, gravity waves can lead to the formation of clouds – a wave that pushes air upwards will trigger cloud formation as the air cools. Other times, gravity waves can trigger ripples in the sky, where clouds form in lines as air alternates up and down. At this spot, particularly during the month of May, the wave comes in at just the right altitude and with the right movement to hit these clouds and actually push the air downwards where the clouds vanish.
The scientists who identified this cloud erosion suggest that a series of dropsondes, sensors dropped from planes that are commonly used to measure air conditions in hurricanes, could be targeted at one of these wave fronts to see how much the air is moving and how exactly it triggers cloud collapse. Kinda neat to watch!
-JBB
Video credit and original paper: http://science.sciencemag.org/content/361/6403/697
Perfect lenticular cloud over Lanin volcano, Patagonia - look how the wispy waves form and then vanish just as they cross the peak. Such thermodynamics!
Adiabatic Process
Introduction An adiabatic process in thermodynamics is one in which no heat is exchanged between a system and its surroundings. The word “adiabatic” comes from Greek roots meaning “impassable,” referring to the heat transfer. This concept is of paramount importance in the study of thermodynamics, heat engines, and atmospheric physics. Adiabatic Condition The condition for an adiabatic process…
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Compressed Air Energy Storage Market Present Scenario And The Growth Prospects 2030
It is highly unlikely that the demand for energy will ever decrease. The way the population around the globe is increasing, the energy requirement will only increase. However, the conventional ways of generating energy are now unable to fulfil this rapidly growing need for power. In addition to this, the excessive utilization of non-renewable resources has resulted in global warming. The International Energy Association has estimated that for keeping global warming below 2 degree Celsius, about 266 GW of energy is required to be stored by 2030, globally, rising from 176.5 GW in 2017.
It is due to these factors that the demand for alternative ways of generating and storing clean energy is increasing day by day, which, in turn, is resulting in the growth of the global compressed air energy storage market. The dependence on renewable sources for generating energy is rising across the globe. Different form of renewable energy, such as solar and wind, are largely dependent on energy storage systems, owing to which, the need for adopting different types of storage systems is rising as well. One of such systems is the compressed air energy storage, which is based on gas turbine cycle.
Excessive power is utilized for compressing air by making use of a rotary compressor, which is then stores in an underground chamber. In case power is needed, the compressed air is released from the chamber and is passed through an air turbine, which produces electricity from the flowing high-pressure air. Different types of compressed air energy storage are diabatic, adiabatic, and isothermal. Out of all these, the demand for diabatic type is predicted to increase considerably in the years to come. This is majorly ascribed to the simple design and lower operating cost of this type, as compared to isothermal and adiabatic compressed air energy storage systems.
In addition to this, isothermal and adiabatic compressed air energy storage systems are still in the developmental phase, which is why, the industry is dominated by diabatic compressed air energy storage systems. When geography is taken into consideration, North America is predicted to emerge as a major compressed air energy storage market in the near future, which is primarily due to the surging requirement for electricity storage systems in the region. According to the Environmental and Energy Study Institute, the U.S. produced 4 billion megawatt-hours of electricity, however only 431 megawatt-hours of power was stored in 2017.
In conclusion, the demand for compressed air energy storage systems is growing due to the surging population, increased consumption of fossil fuels, rapid degradation of the environment, and rising dependence on alternative resources for generating energy.