Atmospheric Science: The Lost Level

The Lost Level

Lurking in the US Standard Atmosphere 1976 is a rather surprising concept that Atmospheric Science appears to have lost down the back of the sofa in recent years.

There may be many very valid reasons for the disappearance of the Isopycnic Level.

However, it is also possible that the Isopycnic Level is a very inconvenient concept that falsifies some modern computer models developed by the Settled Science Brigade.

First off: What is the Isopycnic Level?

The US Standard Atmosphere 1976 can be used to construct the following definition:

1) The Isopycnic Level is where the Density of Air has been observed to vary by less than two percent [relative to the 1976 standard].

2) The Isopycnic Level is at an altitude of about 8 kilometres in the Earth’s Atmosphere,

1976 - Isopycnic Level
US Standard Atmosphere 1976

The concept of the Isopycnic Level originated in 1924 when [the researcher] Sen concluded that “below 8 km air density was controlled primarily by air temperature but above 8 km primarily by pressure changes”.

Designers and engineers need information on the distribution of density to extreme altitudes to predict the performance of missiles, satellites, and aircraft.

Density is the defining parameter for model atmospheres above 80 km, because it is measured more accurately at high altitudes than either pressure or temperature.

The first systematic investigation of the combined effect of pressure and temperature on atmospheric density at various elevations above the earth’s surface (Sen, 1924) was limited by available data to the first 10 km of the earth’s atmosphere.

Examining the seasonal changes in the slopes of various equisubstantial surfaces (isopycnic surfaces) from pole to equator, Sen found that as density increased below 8 km it became less above 8 km, and, conversely, a decrease below 8 km accompanied an increase above.

He concluded that below 8 km air density was controlled primarily by air temperature but above 8 km primarily by pressure changes.

Sen proposed the names thermosphere and barosphere for the atmospheric layers below and above 8 km, respectively, and thermopause for the neutral layer at approximately 8 km, where he found that density remained constant during all seasons and at all locations over the whole globe.

These terms were never adopted, but the isopycnic level at 8 km and the seasonal changes in the structure of the atmosphere which he described have been recognized by other researchers.

Humphreys (1929), DoPorto (1943), Morgan (1948), and others have extended Sen’s study to altitudes up to 25 km.

Suggestion of a Second Isopycnic Level at 80 to 90 Kilometers over Churchill, Canada
Allen E. Cole – Journal of Geophysical Research – 01/1961;

The research of Cole and Court in 1962 clearly supported the concept of the Isopycnic Level.

1964 - US Isopycnic Level
in- formation
Comments on “Density Variation and Isopycnic Layers”
Allen E Cole – Air Force Cambridge Research Laboratories, Bedford, Mass.
American Meteorological Society – Notes and Correspondence – December 1964

1962 - Supplemental Atmospheres
Research Note – Supplemental Atmospheres – 1962
A. Court, A. J. Kantor, A. E. Cole
Armed Services Technical Information Agency – Arlington, Virginia

Additionally, the research by Smith, McMurray and Crutcher in 1963 demonstrated that the air density at an altitude of 8 kilometres was within [plus or minus] two percent of 520 grams per cubic metre in the Northern Hemisphere [up to 80 degree north].

1964 - Isopycnic Densities

Comments on “Density Variation and Isopycnic Layers”
Allen E Cole – Air Force Cambridge Research Laboratories, Bedford, Mass.
American Meteorological Society – Notes and Correspondence – December 1964

Visual evidence suggesting the presence of the Isopycnic Level [where the regime changes from temperature controlled to pressure controlled] is the anvil feature associated with cumulonimbus clouds.

Cumulonimbus Anvil

However, from the early 1960s it appears the Isopycnic Level was problematical because the mainstream considered developing “a better understanding of the lower atmosphere” so they could “explain the observed level of constant density at about 8 km (isopycnic level)”.

1963 - Density Distribution

Density Distribution as Inferred by the Wind Field and Static Forces
V S Whitehead, D E Pitts and E F Blick
Atmospheric Research Laboratory – University of Oklahoma Research Institute
American Institute of Aeronautics and Astronautics – 1963

Perhaps the mainstream even reconsidered Sen’s conclusion [from 1924] that “below 8 km air density was controlled primarily by air temperature but above 8 km primarily by pressure changes”.

Sadly, the history of the Isopycnic Level appears to fizzle out in the 1970s.

At about 8 km the density is nearly constant in time and space.

This level, which is near the 350-mb pressure surface, is called the ISOPYCNIC LEVEL, a level of constant density.

This level is the location of the upper tropospheric maximum of interdiurnal pressure variation, with mass variations of opposite sign above and below this level.

Since the density at 200 millibars is only four-sevenths the density at the isopycnic level, the height change at 200 millibars would be almost twice that a 350 millibars for the same pressure change at corresponding geometric levels. Thus height changes in the lower stratosphere tend to be a maximum even though pressure changes are a maximum at the isopycnic level which is usually below the midlatitude tropopause.

The large pressure variations at the isopycnic level require TEMPERATURE variations for constancy of density. Since the density is nearly constant in space at this level, the required temperature variations must result from vertical motions.

When the pressures are rising at this level, the temperature must also rise to keep the density constant. A temperature rise can be produced by descending motion. Similarly falling pressures at this level require falling temperatures to keep the density constant. Falling temperatures in the absence of advection can be produced by ascent through this level.

Thus, rising heights at the pressure level of constant density are associated with subsidence and falling heights of this surface are associated with upwelling.

Subsidence at 350 millibars can result from horizontal CONVERGENCE above this level and upwelling here would result from horizontal DIVERGENCE above this level.

Since rising heights in the upper troposphere are also known to be associated with rising of the tropopause and lower stratosphere, the maximum horizontal convergence must occur between the constant density level and the average level of the tropopause (about 250 millibars). This is due to the reversal of sign of the vertical motion between the tropopause and the isopycnic level. Thus, the level of maximum horizontal velocity convergence must be between 300 millibars and 200 millibars and is the causative mechanism for pressure or height rises in the upper air. Similarly, upper height falls are produced by horizontal velocity divergence with a maximum at the same level. The maximum divergence occurs near or slightly above the tropopause and closer to 200 millibars than to 300 millibars.

It is probably more realistic therefore to define a LAYER of maximum divergence and convergence as occurring between the 300- and 200-mb pressure surfaces. This is also the layer in which the core of the Jetstream is usually located. At this level the cumulative effects of the mean temperature field of the troposphere produce the sharpest horizontal contrasts in the wind field.

Aerographers Mate 1 & C: Rate Training Manual – 1974
Naval Training Command, Pensacola, Fla.

Wikipedia clearly ignores the Isopycnic Level and happily focuses upon the relationship between temperature and air density [1.2 kg per cubic metre] at a pressure of one standard atmosphere whilst stating that humid air should be treated as a mixture of to two ideal gases.

Unsurprisingly, mainstream air density always conforms to mainstream theory because air “density is not measured directly but is calculated”.

2014 - Density and Mass

2014 - Density of Air

2014 - Humid Air

Thus the story of the lost Isopycnic Level grinds to an unsatisfactory halt [unless you know differently].

Perhaps there were valid reasons for the mainstream to abandon the concept.

Perhaps the mainstream simply let the concept slide down the back of the sofa.

However, given the mainstream predilection for Settled Science my default assumption is that [somewhere along the line] the mainstream let the dog eat their homework.

Wikipedia actually provides some half-decent information regarding the constituents of the dry air in their article regarding the Density of Air. I can only assume that the Wikipedia article on the Atmosphere of Earth is targeted at young children and Earth Scientists.

2014 - Air Constituents

Dry Air

Gallery | This entry was posted in Atmospheric Science, Earth. Bookmark the permalink.

7 Responses to Atmospheric Science: The Lost Level

  1. mkelly says:

    isopycnic surfaces

    Isopynic Level

    Picky I know but there are two different spelling of the word. I think yours is missing the “c”.

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