The mesopause altitude: Only two distinctive levels worldwide?

Zahn, U. von; Höffner, J.; Eska, V.; Alpers, M.

doi:10.1029/96gl03041

Cited by 97 publications

(85 citation statements)

References 14 publications

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“…SABER observations indicate that there is a pole-to-pole extension of low temperature around 95-100 km that is seen at both solstice seasons. This low temperature has been seen in other observations as well (e.g., von Zahn et al 1996).…”

Section: Zonal Mean Temperature and Windssupporting

confidence: 52%

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Global Dynamics of the MLT

2012

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The transition between the middle atmosphere and the thermosphere is known as the MLT region (for mesosphere and lower thermosphere). This area has some characteristics that set it apart from other regions of the atmosphere. Most notably, it is the altitude region with the lowest overall temperature and has the unique characteristic that the temperature is much lower in summer than in winter. The summer-to-winter-temperature gradient is the result of adiabatic cooling and warming associated with a vigorous circulation driven primarily by gravity waves. Tides and planetary waves also contribute to the circulation and to the large dynamical variability in the MLT. The past decade has seen much progress in describing and understanding the dynamics of the MLT and the interactions of dynamics with chemistry and radiation. This review describes recent observations and numerical modeling as they relate to understanding the dynamical processes that control the MLT and its variability. Results from the Whole Atmosphere Community Climate Model (WACCM), which is a comprehensive high-top general circulation model with interactive chemistry, are used to illustrate the dynamical processes. Selected observations from the Sounding the Atmosphere with Broadband Emission Radiometry (SABER) instrument are shown for comparison. WACCM simulations of MLT dynamics have some differences with observations. These differences and other questions and discrepancies described in recent papers point to a number of ongoing uncertainties about the MLT dynamical system.

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Section: Zonal Mean Temperature and Windssupporting

confidence: 52%

“…1). However, in the summer high latitudes, the mesopause temperature is much lower, and its altitude is lower (von Zahn et al 1996;Xu et al 2007a). The global low temperature at 95-100 km is due to the radiative balance there.…”

Section: Zonal Mean Temperature and Windsmentioning

confidence: 99%

Global Dynamics of the MLT

2012

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“…Recently, a new generation of solid-state laser has been developed by van Zahn and H6ffner [1996] for measuring both K density and K temperature. Three previous studies of the seasonal behavior of the K layer at midlatitudes have established that the peak density of the layer is very similar in winter and summer, with either a marginal increase in the column abundance during winter [Graham et al, 1971;Megie et al, 1978] or a small decrease [van Zahn and H6ffner, 1996]. This is an important contrast with the Na layer, where in winter there is a threefold to fourfold increase in both peak density and column abundance at midlatitudes [Megie et al, 1978;Kane and Gardner, 1993;Plane et al, 1999], and there is an even greater seasonal variation at high latitudes [Tilgner and van Zahn, 1988; Kurzawa and van Zahn, 1990].…”

Section: Paper Number 1999ja900117mentioning

confidence: 99%

The terrestrial potassium layer (75–110 km) between 71°S and 54°N: Observations and modeling

Eska¹,

Zahn²,

Plane³

1999

J. Geophys. Res.

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Abstract. Observations of the nighttime atmospheric potassium layer were performed on the German research vessel Polarstem from March to June 1996. K density profiles were obtained between 71øS and 45øN. The nightly mean peak densities ranged from 140 cm -3 in the equatorial region to 10 cm -3 in the Antarctic, and the column abundances decreased from 1.2 x 108 to 1.3 x 107 cm -2 going from low to high latitudes. High peak densities and column abundances were also commonly observed together with sporadic K layers. The global mean peak height of the normal (background) K layer was found to be 88.3 km. After the Polarstern campaign, observations were continued at Kfihlungsborn (54øN). The summer and winter K layers, observed during July 1996 and January 1997, were quite different in shape but had similar peak densities and column abundances. A one-dimensional model of the K layer was developed which includes meteoric deposition, vertical transport through eddy diffusion, and a full chemical scheme. This model was able to reproduce very satisfactorily the seasonal behavior of the K layer at 54øN if the wintertime deposition flux of the metal was reduced by 30% compared to the summer. The midlatitude ratio of K to Na was about 1%, much less than either the chondritic or cosmic ratios of the two metals (•8 or 6%, respectively). The most likely reason is that potassium vaporizes less efficiently from meteoroids than sodium, in agreement with a thermodynamic model of a nonideal chondritic magma and observations in the exosphere of Mercury. Finally, the model was generally very successful in reproducing the latitudinal variations in the K layer. IntroductionThe deposition of extraterrestrial material in the Earth's upper atmosphere gives rise to layers of free neutral metal atoms in the altitude range from 80 to 110 km [Plane, 1991]. Investigations of the K layer were initiated by Lytle and Hunten [1959], who were able to estimate the ratio of potassium to sodium. Some years later, Sullivan and Hunten [1962, 1964] determined the peak density and column abundance from weak twilight emission data by using a birefringent filter photometer. These measurements were continued by Gault and Rundle [1969] The first model of mesospheric potassium was developed by Swider [1987] from an existing model of sodium chemistry. He proposed that the seasonal differences between Na and K might be explained by the kinetics of key potassium reactions having smaller temperature dependences than their sodium analogues. However, the sodium model that he used was quite 17,173

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“…The two-level structure of the mesopause altitude is an intriguing feature of the MLT region. Ground-based measurements have observed and characterized the two-level structure of the mesopause at select geographic locations for many years (von Zahn et al, 1996;She and von Zahn, 1998; and references therein). However, SABER measurements are providing the first continuous global measurements of the MLT thermal structure, an invaluable dataset for understanding the evolution and mechanisms responsible for this striking feature of the MLT region (e.g., Berger and von Zahn, 1999).…”

Section: Mlt Kinetic Temperaturementioning

confidence: 99%

Kinetic temperature and carbon dioxide from broadband infrared limb emission measurements taken from the TIMED/SABER instrument

Mertens¹,

Russell²,

Mlynczak³

et al. 2009

Advances in Space Research

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The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) experiment is one of four instruments on NASA's Thermosphere-Ionosphere-Energetics and Dynamics (TIMED) satellite. SABER measures broadband infrared limb emission and derives vertical profiles of kinetic temperature (Tk) from the lower stratosphere to approximately 120 km, and vertical profiles of carbon dioxide (CO 2 ) volume mixing ratio (vmr) from approximately 70 km to 120 km. In this paper we report on SABER Tk/CO 2 data in the mesosphere and lower thermosphere (MLT) region from the version 1.06 dataset. The continuous SABER measurements provide an excellent dataset to understand the evolution and mechanisms responsible for the global two-level structure of the mesopause altitude. SABER MLT Tk comparisons with ground-based sodium lidar and rocket falling sphere Tk measurements 2 are generally in good agreement. However, SABER CO 2 data differs significantly from TIME-GCM model simulations. Indirect CO 2 validation through SABER-lidar MLT Tk comparisons and SABER-radiation transfer comparisons of nighttime 4.3 µm limb emission suggest the SABER-derived CO 2 data is a better representation of the true atmospheric MLT CO 2 abundance compared to model simulations of CO 2 vmr.

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The mesopause altitude: Only two distinctive levels worldwide?

Cited by 97 publications

References 14 publications

Global Dynamics of the MLT

Global Dynamics of the MLT

The terrestrial potassium layer (75–110 km) between 71°S and 54°N: Observations and modeling

Kinetic temperature and carbon dioxide from broadband infrared limb emission measurements taken from the TIMED/SABER instrument

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