alexa chung mulberry Atmospheric lapse rate

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The atmospheric lapse rate ( ) refers to the change of an atmospheric variable with a change of altitude, the variable being temperature unless specified otherwise (such as pressure, density or humidity).[1][2][3] While usually applied to Earth’s atmosphere, the concept of lapse rates can be extended to atmospheres (if any) that exist on other planets.

Lapse rates are usually expressed as the amount of temperature change associated with a specified amount of altitude change, such as 9.8 K per kilometre, 0.0098 K per metre or the equivalent 5.4 F per 1000 feet. If the atmospheric air cools with increasing altitude, the lapse rate may be expressed as a negative number. If the air heats with increasing altitude, the lapse rate may be expressed as a positive number.

The lapse rate is most often denoted by the Greek capital letter Gamma, or ,[4] but not always. Standard Atmosphere uses L to denote lapse rates:[5] A few others use the Greek lower case letter gamma, , which is an unfortunate choice since gamma is also used for the specific heat ratio.

Types of lapse rates

There are three types of lapse rates that are used to express the rate of temperature change with a change in altitude, namely the dry adiabatic lapse rate, the wet adiabatic lapse rate and the environmental lapse rate.

Dry adiabatic lapse rate

Since the atmospheric pressure decreases with altitude (see Earth’s atmosphere), the volume of an air parcel expands as it rises. Conversely, if a parcel of air sinks from a higher altitude to a lower altitude, its volume is compressed by the higher pressure at the lower altitude. An adiabatic lapse rate is the rate at which the temperature of an air parcel changes in response to the expansion or compression process associated with a change in altitude, under the assumption that the process is adiabatic (meaning that no heat is added or lost during the process).[6][7]

Earth’s atmospheric air is rarely completely dry. It is also often referred to as the dry adiabat, DALR or unsaturated lapse rate. water vapor may be and usually is present.

The dry adiabatic lapse rate can be mathematically expressed as:[8][9]

= the specific heat of dry air at constant pressure, 1004.64 J/(kg K)

The troposphere is the lowest layer of the Earth’s atmosphere. Since and vary little with altitude, the dry adiabatic lapse rate is approximately constant in the troposphere. At that dew point temperature, the air parcel is saturated and, because of the release of the heat of vaporization, the rate of cooling will decrease to what is known as the wet adiabatic lapse rate. This rate is also often referred to as the wet adiabat, saturated lapse rate,
alexa chung mulberry Atmospheric lapse rate
SALR, moist adiabatic lapse rate or MALR.[6][7]

The wet adiabatic lapse rate is not a constant since it depends upon how much water vapor the atmospheric air contained when it started to rise, which means the amount of heat of vaporization available for release is variable. In the troposphere, the rate can vary from about 4 K/kilometre (2.2 F/1000 ft) in regions where the ambient temperature is about 25 C (77 F) to about 7 K/kilometre (3.8 F/1000 ft) in regions where the ambient temperature is about 10 C (14 F).

After the air parcel has reached its dew point and cooling has decreased to the wet adiabatic lapse rate, it will eventually rise to a point where all of its water vapor has condensed and its rate of cooling will then revert back to the dry adiabatic lapse rate.

The wet adiabatic lapse rate can be mathematically expressed as:[10]

Environmental lapse rate

The dry adiabatic lapse rate and the wet adiabatic lapse rate are both theoretical rates. The actual real world profile of temperature versus altitude that exists at any given time and in any given geographical location is called the environmental lapse rate, also often referred to as the ELR, prevailing lapse rate or ambient lapse rate.[6][7][11]

Meteorologists measure vertical temperature profiles by releasing weather balloons with mini weather stations attached to them called radiosondes. Sometimes, meteorologists drop these mini weather stations from an airplane at high altitude with a parachute attached. This type of measuring device is called a dropsonde.

In general, the ambient atmospheric air in the troposphere decreases with increasing altitude and so the environmental lapse rate is denoted as being negative. Standard Atmosphere[5] having various values, as shown in the adjacent table, which are dependent on the altitude region of Earth’s atmosphere. Standard Atmosphere is 6.5 K/km (3.57 F/1000 feet). Standard Atmosphere for altitudes up to 11 km (6.8 miles)

The adjacent graph, published by the United States National Weather Service (NWS),[14] depicts the average profile of temperature versus altitude in the various layers the Earth’s atmosphere. Standard Atmosphere.

At times, inversion layers may form in the troposphere. Such inversion layers will have a positive environmental lapse rate, meaning that the atmospheric temperature increases with altitude within the inversion layers[11]. An inversion layer may be one of two types:

Surface inversion layer

During the night, the Earth’s surface loses heat rather rapidly by radiation while the ambient air above the surface looses heat more slowly by convection. Thus, what is called a radiation inversion forms in which the air temperature for some distance above the ground is higher than the air temperature very near to the ground. In other words, the environmental lapse rate within the surface inversion layer is positive and increases with altitude. Air very near Earth’s surface which has flowed across a cold surface (such as a lake), and been cooled by advection, may also form a surface inversion layer called an advective inversion. As it rises, it forms what is called an inversion aloft. The height of the lid is called the mixing height. As the day goes on and the Earth’s surface continues to warm, the base of the inversion rises, the inversion layer gets thinner and the mixing height increases. When the base of the layer reaches the inversion top, perhaps by mid afternoon on a hot summer day, the inversion aloft breaks up completely and the mixing height is no longer limited.[11]
alexa chung mulberry Atmospheric lapse rate