Adiabatic Cooling and Lapse Rates Explained

Chapter 10 Adiabatic processes, lapse rates and rising air

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Summary

Temperature changes in the air can occur through diabatic and adiabatic processes. Diabatic processes involve direct energy exchanges, like heating over a surface, while adiabatic processes involve no net energy exchange, instead depending on compression or expansion. As air rises, it expands and cools at a rate of 10°C per 1,000 meters (dry adiabatic lapse rate). If condensation occurs, the rate changes to the moist adiabatic lapse rate, which is less intense due to released energy. Several mechanisms including orographic lifting and frontal lifting cause air to rise, affecting the environmental lapse rate, which varies based on factors like solar radiation and pressure. Temperature impacts air density, with warmer, less dense air rising, and cooler, denser air sinking.

Highlights

Diabatic processes involve direct energy exchanges such as heating over a hot surface.
Adiabatic processes occur with no net energy exchange, relying on air compression or expansion.
Rising air cools at 10°C per 1,000m (dry adiabatic lapse rate) until condensation begins.
Condensation slows cooling, changing to a moist adiabatic lapse rate (approximately 5°C per 1,000m).
Orographic lifting causes air to rise over mountains, leading to cloud formation and potential rain. ⛰️
Frontal lifting and convection promote air rise, influencing weather conditions.
Environmental lapse rates vary with surface heating, leading to variations in local temperatures.
Air density and temperature are inversely related, impacting an air parcel's rising or sinking behavior.

Key Takeaways

Air temperature changes through diabatic (energy exchange) and adiabatic (compression/expansion) processes. 🌡️
Rising air cools and expands at the dry adiabatic lapse rate unless condensation slows cooling. 🌧️
Mechanisms like orographic lifting and convection cause air to rise, affecting weather patterns. 🌄
Environmental lapse rates vary due to factors like surface temperature and solar radiation. ☀️
Air density and temperature are inversely related; warmer air is less dense and rises. 🪂

Overview

Adiabatic processes play an important role in the atmosphere without needing a net energy change. When air rises and faces lower atmospheric pressure, it expands and cools at a steady rate known as the dry adiabatic lapse rate, typically around 10°C per 1,000 meters. Once moisture in the air begins to condense, the rate of cooling slows due to the extra energy released. This slower rate is called the moist adiabatic lapse rate.

Several natural mechanisms might trigger the rise of air parcels, including features like mountains and changing weather fronts. As air climbs over a mountain range, for instance, orographic lifting can cool it enough to form clouds and bring rain on the windward side. Beyond just mountains, different lapse rates explain how air heats or cools differentially across various heights, informed by factors like sunlight or pressure changes.

Understanding these atmospheric processes helps predict weather patterns, including where clouds and precipitation might form. It sheds light on why certain areas, like the rain shadow deserts, remain dry while nearby regions receive ample rain. This knowledge aids meteorologists and climate scientists in forecasting changes and recognizing patterns crucial for predicting local weather events.

Chapters

00:00 - 01:30: Adiabatic and Diabetic Processes The chapter explains two primary methods of changing the temperature of an air parcel: diabetic and adiabatic processes.
01:30 - 02:30: Air Parcel Expansion and Cooling The chapter discusses the concept of air parcel expansion and cooling. It uses the analogy of a diabetic process to describe how air molecules behave in a chamber. At high temperatures, the molecules possess high kinetic energy and move rapidly. Compressing the air results in the molecules moving even faster, indicating an increase in temperature. Conversely, when the air is expanded, the molecules slow down, demonstrating a cooling effect.
02:30 - 04:30: Adiabatic Lapse Rates The chapter explains the concept of adiabatic processes, focusing on the adiabatic lapse rate, which describes how air cools as it rises into regions of lower pressure.
04:30 - 06:30: Environmental Lapse Rate The chapter addresses the concept of environmental lapse rate. It explains that if an air parcel rises, it will expand and cool, whereas if it sinks, it will contract and warm. This phenomenon occurs as long as no condensation is involved, and the temperature change occurs at a fixed rate, known as the dry adiabatic lapse rate.
06:30 - 09:30: Mechanisms of Air Parcel Lifting The chapter discusses the concept of the adiabatic lapse rate, which is the rate at which air temperature decreases with an increase in altitude. It specifically mentions that the adiabatic lapse rate is 10°C per 1,000 meters. For example, if the surface air temperature is 32°C and the air rises to 1,000 meters, the temperature decreases to 22°C. If it rises to 2,000 meters, the temperature further decreases to 12°C.
09:30 - 12:00: Buoyancy and Gravitational Forces This chapter explains the interplay between buoyancy and gravitational forces, emphasizing the behavior of air parcels. As an air parcel rises, it cools at a rate of 10 degrees per 1,000 meters. Once lifted high enough, the temperature drops to a point where the parcel can no longer hold its water vapor, reaching saturation. This height is known as the lifting condensation level, above which further ascent leads to condensation.

Chapter 10 Adiabatic processes, lapse rates and rising air Transcription

00:00 - 00:30 there are basically two ways in which the temperature of an air parcel can be changed so-called diabetic processes involve Direct Energy exchanges an example is the heating or cooling of the air as it moves across a hot or cold surface so-called adiabetic processes do not involve net energy exchange heating or cooling is achieved by compression or expansion of the
00:30 - 01:00 air here is how a diabetic processes work imagine you have air molecules flying around in a chamber high temperature means that the molecules have high kinetic energy they're flying very fast if I compress the air then the air molecules will start flying faster which means that the air is getting warmer when I expand the air again the air mole mules are flying at a slower
01:00 - 01:30 speed or in other words the air cools down that is an adiabatic process that backs the question how air in nature is compressed or expanded remember that air pressure decreases with altitude so if an air passel rises for whatever reason it will get into a region of lower air pressure as a result it will
01:30 - 02:00 expand and cool if we force an air parel to rise it will expand and cool if we force an air parcel to sink it will contract and warm as long as there is no condensation involved the temperature of a rising air passle decreases at a fixed rate this rate is called the dry
02:00 - 02:30 adiabetic lapse rate it is 10° C per 1,000 M that means if your surface air temperature happens to be 32° C and you force the air to rise up to 1,000 M the temperature will be 22° C you force it up to 2,000 M it will cool down another 10° so its temperature is 12° and so on
02:30 - 03:00 the opposite happens when you force it to come down it will increase its temperature again at 10° per 1,000 M if an air parcel is lifted high enough it will eventually get so cold that it cannot hold the water vapor any longer this is the height at which saturation occurs it is also called the lifting condensation level because further lifting will cause condensation
03:00 - 03:30 condensation means that water vapor gets from the gases into the liquid States we see the formation of clouds in this example the dupoint temperature which as you know depends on the water vapor content of the air is 2° C at 3,000 M the air reaches its dueo 2° C so any further lifting will cause further condensation and formation of the cloud the pro process of condensation releases
03:30 - 04:00 energy therefore the rate at which the air temperature decreases from the lifting condensation level upward will be less the air parcel still expands it still cools down but not So Much Anymore due to the fact that energy is released through condensation beyond the lifting condensation level air Parcels cool at the moist adiabetic lapse rate which is
04:00 - 04:30 approximately 5° C per 1,000 M it is also called saturated or wet adiabetic laps rate the real value can be between 4 and 9° C per thousand M depending on the amount of water vapor that condenses during the lifting remember that the dry and wet adiabatic laps rates are values for the temperature decrease of a lifted air parcel these are not values for
04:30 - 05:00 temperature decrease with altitude that can be measured by taking temperature readings at different altitudes in Chapter 2 we have already talked about the fact that the temperature within the troposphere decreases with altitude this decrease of temperature with altitude is expressed by the so-called environmental laps rate ELR which is also named ambient laps rate similar to the other laps rates it's
05:00 - 05:30 expressed in temperature difference per 1,000 M altitude difference the environmental laps rate varies with time and place it depends strongly on Surface temperatures solar radiation causes surface heating during the day this generally leads to high temperatures near the surface and consequently a high environmental laps rate in the lower atmosphere terrestrial radiation causes
05:30 - 06:00 surface cooling during the night which typically results in a small environmental abps rate when the near surface air is even colder than the upper air we call this a temperature inversion the horizontal transport of air called advection is another factor that influences the environmental lapse rate advection of cold or warm air at different levels for for example due to
06:00 - 06:30 varying wind direction with altitude causes changes in the environmental laps rate I mentioned earlier that adiabetic cooling occurs when air expands because it is lifted four principal mechanisms can initiate the lifting of an air parcel orographic lifting frontal lifting convergence and convection orographic
06:30 - 07:00 uplift occurs when mountains act as barriers to the flow of air air ascends the mountain slope causes adiabetic cooling this often generates clouds many of the world's rainiest places are located on Windward Mountain slopes when air reaches the leward side of the mountain much of the moisture has been lost air descends warms ad
07:00 - 07:30 diabatically and condensation and precipitation are not likely the results are rain shadow deserts such as the Great Basin Desert in the Western United States and the Patagonia desert in Argentina the rising air on the windward side of the mountain range cools first dry a diabatically and later wet adiabatically the sinking air on the leward side of of the mountain range
07:30 - 08:00 warms only dry air diabatically the results are warm Downs slope winds on the leeward side such as the chinuk winds in the Rocky Mountains or the fern winds in the Alps a front is a line where cold and warm air masses Collide this causes the lifting of warm air which is called frontal lifting a low press Center also called called a cyclone always causes air to
08:00 - 08:30 converge horizontal convergence always causes air to rise free convection occurs when air is lifted as the result of heating near the surface this is localized over fairly limited areas and can result in localized Thunders showers
08:30 - 09:00 e e
09:00 - 09:30 so what makes air rise in nature there
09:30 - 10:00 are two forces working on an air parcel gravitational force tries to pull it down to the Earth's surface buoyancy Force tries to pull it upward buoyancy force is simply the result of the fact that we have higher air pressure near the ground low air pressure in the upper atmosphere and as a result air should be moving
10:00 - 10:30 upward given that these two forces gravitational force and bancy force are at an equilibrium there is as of now no reason for an air parcel to rise or sink however that changes when the density of the air parel changes if you have an air parel that has a higher density than its surrounding air then it will sink towards the Earth's surface if the density of of the air parcel is
10:30 - 11:00 lower than the surrounding air then it will rise but what determines the density of air the answer is simple it's the temperature lower temperature higher density higher temperature lower density so an air parcel that is warmer than its surrounding will rise an air parcel that is colder than its surrounding will sink