Change in turbopause altitude at 52 and 70° N

Hall, Chris M.; Holmen, S. E.; Meek, C. E.; Manson, A. H.; Nozawa, Satonori

doi:10.5194/acp-16-2299-2016

Cited by 15 publications

(17 citation statements)

References 47 publications

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“…Offermann et al () defined the wave turbopause as the altitude at which the two lines fit to the regions of small temperature fluctuations at low altitudes and high fluctuations at higher altitudes intersect (see also Hall et al, , ; John & Kishore Kumar, ; Offermann et al, ). The standard deviations are a proxy for wave amplitudes, so where they increase less than exponentially, dissipation is significant.…”

Section: Methodsmentioning

confidence: 99%

“…In Earth's atmosphere the transition region has been studied extensively through a variety of techniques. The turbopause has been determined from observations of sodium clouds ejected by sounding rockets (Lehmacher et al, ) and through turbulent energy dissipation rates from radar measurements (Hall et al, , ); the homopause from profiles of mixing ratios (Danilov et al, ; Offermann et al, ); and the wave turbopause from studies of wave dissipation (Offermann et al, , ). Furthermore, studies of this transition region on Earth have informed our understanding of the dominant processes in the middle atmosphere and their consequences.…”

Section: Introductionmentioning

confidence: 99%

“…Gravity wave amplitudes and drag peak in the lower thermosphere where dissipation is substantial. Turbopause altitudes have been shown to have latitudinal, seasonal, and long‐term changes (Hall et al, , ; Holmen et al, ; Offermann et al, ). Such changes reflect the spatial and temporal variability of all the processes described above and lead to an altitude and latitude‐dependent energy budget (Gardner et al, ; Yigit & Medvedev, ), seasonal distribution of species (Vlasov & Kelley, ), and circulation of the mesosphere and thermosphere (Lindzen, ).…”

Section: Introductionmentioning

confidence: 99%

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Variability of Martian Turbopause Altitudes

et al. 2018

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The turbopause and homopause represent the transition from strong turbulence and mixing in the middle atmosphere to a molecular-diffusion-dominated region in the upper atmosphere. We use neutral densities measured by the Neutral Gas and Ion Mass Spectrometer on the Mars Atmospheric and Volatile EvolutioN spacecraft from February 2015 to October 2016 to investigate the temperature structure and fluctuations of the Martian upper atmosphere. We compare those with temperature measurements of the lower atmosphere from the Mars Reconnaissance Orbiter's Mars Climate Sounder. At the lowest Mars Atmospheric and Volatile EvolutioN altitudes we often observe a statically stable region where waves propagate freely. In contrast, regions from about 20 km up to at least 70 km are reduced in stability where waves are expected to dissipate readily due to breaking/saturation. We derive homopause altitudes from Neutral Gas and Ion Mass Spectrometer N 2 and Ar densities and find that it varies between 60 and 140 km. From the standard deviations in monthly averaged temperature profiles, we determine the wave turbopause altitude where applicable and find that these altitudes agree with the homopause altitudes. We show that the homopause variability is driven by order of magnitude changes in CO 2 densities, which drastically affect the altitude at which the eddy diffusion is equal to the molecular diffusion. These variations are observed as a function of local time, latitude, and season. That the turbopause/homopause does not track a fixed density level means that the eddy diffusion coefficient at the turbopause can vary significantly, suggesting differences in the dominant breaking waves and tidal modes. Plain Language SummaryThe gases that make up a planet's atmosphere are mixed together efficiently near the surface. But in the uppermost part of the atmosphere, gases separate by mass-heavier ones are held closer to the planet, while lighter ones are more abundant higher up. Because turbulence is responsible for the mixing in the atmosphere, the altitude where this transition occurs is called the turbopause. That turbulence is thought to be generated by atmospheric waves that lose energy (somewhat like ocean waves breaking at shore). In this work, we use measurements of the upper atmosphere from Mars Atmosphere and Volatile Evolution Mission and of the lower atmosphere from Mars Reconnaissance Orbiter to study the turbopause region during a full Mars year. Similar to Earth's atmosphere, we find that below the turbopause wave breaking is strong (which produces turbulence), but above waves can move freely. We also show that the turbopause varies significantly depending on the season and location on the planet. At Mars, gases can escape from the top of the atmosphere, so the relative amounts of escape of different gases depends on the turbopause. Understanding this altitude and why it varies is important for interpreting how the atmosphere evolved. Key Points:• Mars's turbopause is governed by the transition from strong wave dissipation ...

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Variability of Martian Turbopause Altitudes

et al. 2018

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“…The downward trends in height of maximum velocities evident in Figure 8 are only applicable to summer conditions and may not apply in other seasons. For example, Hall et al (2016) note that changes in the height (z) in the 81-to 85-km-height range in local summer. However, numerical model simulations that take into account trends in greenhouse gas concentrations such as CO 2 , H 2 O, and ozone in the middle atmosphere report density decreases ranging between −2% and −6% per decade in the MLT (Akmaev et al, 2006;Qian et al, 2013).…”

Section: Trendsmentioning

confidence: 99%

Trends and Variability in Vertical Winds in the Southern Hemisphere Summer Polar Mesosphere and Lower Thermosphere

et al. 2019

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Direct measurement of mean vertical velocities in the mesosphere‐lower thermosphere (60–110 km) is not possible due to their small values. Here we derive vertical velocities using the divergence of the mean meridional wind over the Antarctic summer pole using MF radar wind measurements made at Davis Station (69°S, 78°E) between 1994 and 2018. Estimates of vertical velocity are restricted to a 21‐day period centered just after solstice when the equatorward wind reaches its maximum value of about 15 m s−1 at heights near 90 km. The Medium Frequency (MF) radar winds are calibrated against colocated meteor wind radar observations. Neutral densities required for the vertical wind calculations are obtained from zonally averaged temperature measurements obtained by the MLS instrument aboard the AURA satellite. The estimated vertical velocities have peak values varying between 2 and 6 cm s−1 with significant interannual variability. While the peak values do not show significant long‐term change, there is a long‐term decrease in the mean height of maximum winds of about 0.6 km per decade that is statistically significant. The interannual variability is linked to the date of transition in the stratospheric zonal circulation from winter eastward to summer westward flow. Meridional and vertical velocities are smaller and peak at lower altitudes during early transitions (20–30 days prior to solstice) than is the case for late transitions that occur at solstice or later.

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“…Danilov et al (1979) carried out an attempt at the Heiss Island station, followed by Offermann et al (1981), presenting ratio decreases with height at higher altitudes rather than a roughly constant 1.2% maintained only in the well-mixed lower atmosphere. Additionally, the turbopause altitudes were identified by Hall et al (Hall, 1998;Hall et al, 2008Hall et al, , 2016 using a medium-frequency (MF) radar to obtain the turbulent intensity that is commonly quantified by estimation of the turbulent energy dissipation rate (ε). However, these mixing coefficients are extremely difficult to measure directly.…”

Section: Introductionmentioning

confidence: 99%

Determination of the “Wave Turbopause” Using a Numerical Differentiation Method

Zhao

Sheng

et al. 2019

JGR Atmospheres

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This paper proposes a new algorithm to determine the wave turbopause based on numerical differentiation using temperature data collected from the Sounding of the Atmosphere using Broadband Emission Radiometry onboard the Thermosphere Ionosphere Mesosphere Energetics Dynamics satellite. The vertical gradient profile of the temperature standard deviation, which serves as a proxy of wave activity, is obtained based on Tikhonov regularization. In the vicinity of the altitude of wave turbopause, wave damping is much reduced, and upward wave propagation occurs with little damping effect. The corresponding vertical gradient profile should reach a maximum with values that are no longer negative. Thus, we determine the wave turbopause as the unique maximum that is the first after the last change in the derivative value from negative to positive. The wave turbopause altitudes determined by this new method agree well with those of previous studies, especially regarding the behavior of the monthly variation. The error of the wave turbopause altitude derived from this new method is 1.9 km, which is much improved from the error of 3.3 km estimated by the previous method. Additionally, latitudinal variations of the wave turbopause altitude for different seasons and their monthly variations for 0°, 30°N, and 70°N latitudes during 2016–2018 are presented. Similar to the mesopause, the wave turbopause also exhibits a two‐level structure with a summer minimum at high latitudes.

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Change in turbopause altitude at 52 and 70° N

Cited by 15 publications

References 47 publications

Variability of Martian Turbopause Altitudes

Variability of Martian Turbopause Altitudes

Trends and Variability in Vertical Winds in the Southern Hemisphere Summer Polar Mesosphere and Lower Thermosphere

Determination of the “Wave Turbopause” Using a Numerical Differentiation Method

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