Lagrangian temperature and vertical velocity fluctuations due to gravity waves in the lower stratosphere

Project Loon has been launching superpressure balloons since January 2013 to provide worldwide Internet coverage. These balloons typically fly between 18 and 21 km and provide measurements of winds and pressure fluctuations in the lower stratosphere. We divide 1560 Loon flights into 3405 two‐day segments for gravity wave analysis. We derive the kinetic energy spectrum from the horizontal balloon motion and estimate the temperature perturbation spectrum (proportional to the potential energy spectrum) from the pressure variations. We fit the temperature (and kinetic energy) data to the functional form T′2 = T′o2[ω/ωο)α, where ω is the wave frequency, ωο is daily frequency, T′o is the base temperature amplitude, and α is the spectral slope. Both the kinetic energy and temperature spectra show −1.9 ± 0.2 power‐law dependence in the intrinsic frequency window 3–50 cycles/day. The temperature spectrum slope is weakly anticorrelated with the base temperature amplitude. We also find that the wave base temperature distribution is highly skewed. The tropical modal temperature is 0.77 K. The highest amplitude waves occur over the mountainous regions, the tropics, and the high southern latitudes. Temperature amplitudes show little height variation over our 18–21 km domain. Our results are consistent with other limited superpressure balloon analyses. The modal temperature is higher than the temperature currently used in high‐frequency gravity wave parameterizations.

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“…Our approach is identical to that used by Podglajen et al . []. We assume that the balloon isopycnic perturbation vertical displacement,

ζ_{B}^{'}

, is related to the isentropic vertical displacement, ζ B = σζ ′, where σ is ~0.3 [ Vincent and Hertzog , ; Podglajen et al ., ].…”

Section: Analysis Of the Loon Datamentioning

confidence: 99%

“…[] and Podglajen et al . [] detail the current approach to Lagrangian analysis of superpressure balloon data. The Boccarra et al approach has been applied to Strateole/Vorcore and Concordiasi balloon campaigns with the goal of assessing the upward momentum flux of gravity waves in the South Polar regions [ Hertzog et al ., ].…”

Section: Introductionmentioning

confidence: 99%

Gravity wave spectra in the lower stratosphere diagnosed from project loon balloon trajectories

et al. 2017

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“…In the western Pacific upper TTL, cirrus are more frequent in the negative vertical temperature gradient phase, the supposed cooling phase of the waves. This difference between the eastern and the western Pacific is probably not due to differences in wave amplitudes or characteristics: indeed, observations suggest that the lower frequency waves responsible for the temperature fluctuations do not show a strong geographic variability within the equatorial region (Podglajen et al, 2016a;Kim et al, 2016 Another reason could be the different mean relative humidities between the two regions, the convective western Pacific being moister on average than the dry eastern Pacific. Two different explanations relying on the different background humidities could then explain the observations.…”

Section: Moist Versus Dry Environmentsmentioning

confidence: 98%

“…In practice, however, the method suggested by Eq. 26 turns out to be difficult to apply to observations, since vertical velocities are dominated by high frequency waves (Podglajen et al, 2016a) whose mean impact cancels out (w ρ ice =0) but which will add noise to the observational estimate. To overcome these issues, we use isentropic coordinates in which reversible motions 10 are filtered out.…”

Section: Quantifying the Impact Of Wave Advection On The Vertical Tramentioning

confidence: 99%

Impact of gravity waves on the motion and distribution of atmospheric ice particles

Podglajen¹,

Plougonven²,

Hertzog³

et al. 2017

Preprint

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Abstract. Gravity waves are an ubiquitous feature of the atmosphere and influence clouds in multiple ways. Regarding cirrus clouds, many studies have emphasized the impact of wave-induced temperature fluctuations on the nucleation of ice crystals. This paper investigates the impact of the waves on the motion and distribution of ice particles, using the idealized 2-D framework of a monochromatic gravity wave. Contrary to previous studies, a special attention is given to the impact of the wind field induced by the wave. 5Assuming no feedback of the ice on the water vapor content, theoretical and numerical analyses both show the existence of a wave-driven localization of ice crystals, where some ice particles remain confined in a specific phase of the wave. The precise location where the confinement occurs depends on the background relative humidity, but it is always characterized by a relative humidity near saturation and a positive vertical wind anomaly. Hence, the wave has an impact on the mean motion of the crystals and may reduce dehydration in cirrus by slowing down the sedimentation of the ice particles. The results also 10 provide a new insight into the relation between relative humidity and ice crystals presence.The wave-driven localization is consistent with temperature-cirrus relationships recently observed in the tropical tropopause layer (TTL) over the Pacific during the Airborne Tropical Tropopause EXperiment (ATTREX). It is argued that this effect may explain such observations. Finally, the impact of the described interaction on TTL cirrus dehydration efficiency is quantified using ATTREX observations of clouds and temperature lapse rate.

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“…It needs to be considered in cirrus ice formation alongside aerosol effects in efforts to ascribe cause to changes in cirrus cloud properties [12,13]. The prevalence of mesoscale vertical wind fluctuations in the upper troposphere and lower stratosphere has been confirmed time and again by a number of observational techniques including aircraft and cloud radar [14], super-pressure balloons [15], and wind profiler [16]. Variability in vertical air velocities causes a major portion of ice crystal number variability in a global model [17].…”

Section: Dynamical and Microphysical Controls Of Cirrusmentioning

confidence: 99%

Cirrus Clouds and Their Response to Anthropogenic Activities

Kärcher

2017

Curr Clim Change Rep

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Cirrus clouds are ubiquitous, long-lived, highlevel ice clouds that exert a considerable global radiative effect on the climate system. This review assesses recent observational and modeling evidence of how anthropogenic activities might affect cirrus. Changes in physical properties and chemical composition of liquid aerosol particles will unlikely affect cirrus significantly, but anthropogenic influences may occur through changes in heterogeneous ice nuclei. Two main uncertain factors contribute to the current inability to constrain background cirrus formation: small-scale variability in dynamical forcings that drive ice nucleation parameterizations and the ability of airborne particles to act as efficient heterogeneous ice nuclei. These uncertainties keep us from drawing robust conclusions about anthropogenic influences on cirrus. Microphysical and macrophysical representation of cirrus in global models must first be advanced before we can predict changes in climate with fewer uncertainties. Some climate intervention studies suggest a potential cooling effect of deliberately perturbed cirrus, but at the risk of modifying precipitation inadvertently.

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Lagrangian temperature and vertical velocity fluctuations due to gravity waves in the lower stratosphere

Cited by 89 publications

References 54 publications

Gravity wave spectra in the lower stratosphere diagnosed from project loon balloon trajectories

Gravity wave spectra in the lower stratosphere diagnosed from project loon balloon trajectories

Impact of gravity waves on the motion and distribution of atmospheric ice particles

Cirrus Clouds and Their Response to Anthropogenic Activities

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