An investigation of subsidence in the free atmosphere

Abstract Aircraft flights through stratocumulus clouds (Sc) during the Dynamics and Chemistry of Marine Stratocumulus II (DYCOMS-II) study off the California coast found narrow in-cloud regions with less liquid water content (LWC) and cooler temperatures than average background values. The regions are named cloud holes and are assumed to be a result of water evaporated by the entrainment of dryer air from above the Sc. While such features have been noted previously, this study provided a unique opportunity to investigate in much greater detail the nature of the holes, as well as their relationship to the entrainment rate, because high-speed temperature and LWC probes with maximum spatial resolution of 10 cm were flown together for the first time. Nine long-duration flights were made through mostly unbroken Sc for which conditional sampling was used to identify the location and size of the holes. The holes are concentrated near cloud top, their average width near cloud top is about 5 m, their relative length distribution is nearly constant for all flights, and they can penetrate hundreds of meters deep into the Sc before being lost by mixing. Entrainment velocities at cloud top are estimated from measurements of fluxes of reduced LWC and vapor mixing ratios in holes, the fraction of cloud area covered by holes, and the total water jump between cloud top and the free atmosphere. Rates as large as 10 mm s−1 are found for nocturnal flights, and these rates are about 3 times larger than for daytime flight segments. The rates correlate best with the size of the buoyancy jump above the Sc; the present conditional-sampling approach for measuring the rates gives larger rates than the “flux jump” rates determined by others for the same flights by a factor of about 2. The stability criterion for all Sc predicts thinning and breakup of the Sc, which does not occur. The minimal amount of cloud-top evaporative cooling caused by entrainment contributes little to the top-down convection dominated by radiative cooling during nocturnal flights; however, evaporative cooling caused by the mixing of holes as they subduct with the large-scale eddy circulation in the Sc may contribute, but with an as-of-yet unknown amount.

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Cumulus over the Tibetan Plateau in the Summer Based on CloudSat–CALIPSO Data

Journal of Climate ◽

10.1175/jcli-d-15-0492.1 ◽

2016 ◽

Vol 29 (3) ◽

pp. 1219-1230 ◽

Cited By ~ 18

Author(s):

Yunying Li ◽

Minghua Zhang

Keyword(s):

Tibetan Plateau ◽

Climate Models ◽

Surface Wind ◽

Lower Atmosphere ◽

The Tibetan Plateau ◽

Shallow Convection ◽

Free Atmosphere ◽

Northern Summer ◽

Static Energy ◽

Fine Resolution

Abstract Cumulus (Cu) can transport heat and water vapor from the boundary layer to the free atmosphere, leading to the redistribution of heat and moist energy in the lower atmosphere. This paper uses the fine-resolution CloudSat–CALIPSO product to characterize Cu over the Tibetan Plateau (TP). It is found that Cu is one of the dominant cloud types over the TP in the northern summer. The Cu event frequency, defined as Cu occurring within 50-km segments, is 54% over the TP in the summer, which is much larger over the TP than in its surrounding regions. The surface wind vector converging at the central TP and the topographic forcing provide the necessary moisture and dynamical lifting of convection over the TP. The structure of the atmospheric moist static energy shows that the thermodynamical environment over the northern TP can be characterized as having weak instability, a shallow layer of instability, and lower altitudes for the level of free convection. The diurnal variation of Cu with frequency peaks during the daytime confirms the surface thermodynamic control on Cu formation over the TP. This study offers insights into how surface heat is transported to the free troposphere over the TP and provides an observational test of climate models in simulating shallow convection over the TP.

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Theoretical and practical aspects of a free-atmosphere tritium exposure system

Journal of Environmental Radioactivity ◽

10.1016/s0265-931x(96)00085-9 ◽

1997 ◽

Vol 36 (2-3) ◽

pp. 141-156 ◽

Cited By ~ 1

Author(s):

B.D Amiro ◽

P.A Davis ◽

F.L Johnston ◽

W.J.G Workman

Keyword(s):

Free Atmosphere ◽

Exposure System

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A New Time-dependent Theory of Tropical Cyclone Intensification

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-21-0169.1 ◽

2021 ◽

Author(s):

Yuqing Wang ◽

Yuanlong Li ◽

Jing Xu

Keyword(s):

Boundary Layer ◽

Tropical Cyclone ◽

Numerical Simulations ◽

Strong Dependence ◽

Surface Wind ◽

Time Dependent ◽

Quasi Equilibrium ◽

Free Atmosphere ◽

Near Surface ◽

Tangential Wind

AbstractIn this study, the boundary-layer tangential wind budget equation following the radius of maximum wind, together with an assumed thermodynamical quasi-equilibrium boundary layer is used to derive a new equation for tropical cyclone (TC) intensification rate (IR). A TC is assumed to be axisymmetric in thermal wind balance with eyewall convection becoming in moist slantwise neutrality in the free atmosphere above the boundary layer as the storm intensifies as found recently based on idealized numerical simulations. An ad-hoc parameter is introduced to measure the degree of congruence of the absolute angular momentum and the entropy surfaces. The new IR equation is evaluated using results from idealized ensemble full-physics axisymmetric numerical simulations. Results show that the new IR equation can reproduce the time evolution of the simulated TC intensity. The new IR equation indicates a strong dependence of IR on both TC intensity and the corresponding maximum potential intensity (MPI). A new finding is the dependence of TC IR on the square of the MPI in terms of the near-surface wind speed for any given relative intensity. Results from some numerical integrations of the new IR equation also suggest the finite-amplitude nature of TC genesis. In addition, the new IR theory is also supported by some preliminary results based on best-track TC data over the North Atlantic and eastern and western North Pacific. Compared with the available time-dependent theories of TC intensification, the new IR equation can provide a realistic intensity-dependent IR during weak intensity stage as in observations.

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Einfluss von Silan-dotierten Umgebungsatmosphären auf tribologischen Eigenschaften von Titan

Tribologie und Schmierungstechnik ◽

10.24053/tus-2021-0002 ◽

2021 ◽

Author(s):

Selina Raumel ◽

Khemais Barienti ◽

Folke Dencker ◽

Florian Nürnberger ◽

Marc C. Wurz

Keyword(s):

Low Temperatures ◽

Surface Oxidation ◽

Wear Volume ◽

Ambient Atmosphere ◽

Free Atmosphere ◽

Metalworking Industry ◽

Tribological System ◽

Identification And Characterization ◽

Ball On Disc

The production processes of the metalworking industry are usually carried out in the presence of oxygen. Par ticularly due to surface oxidation on tools and parts during production under normal atmosphere, high wear is observed in tribological systems. The focus of these investigations is the question to what extent the ambient atmosphere has an influence on the tribological system. For this purpose, the identification and characterization of wear mechanisms in an oxygen-free atmosphere is of high relevance. To analyse the influence of the ambi ent atmosphere on the tribological properties of titanium, ball-on-disc investigations are carried out on a univer sal tribometer (UMT) in an air, argon and silane-anodized atmosphere. By suppressing the oxidation under ex clusion of oxygen, a reduction of the tribochemical wear could be shown, which is accompanied by a reduction of the wear volume by a Factor of 4.5. However, due to the adhesion of both friction partners, which already occurs at low temperatures, caused by the omission of the friction-reducing cover layers, the friction coefficient increased. In addition, novel alloy formations at the interfaces were detected and analysed.

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Aviation and turbulence in the free atmosphere

Weather ◽

10.1002/wea.2318 ◽

2014 ◽

Vol 69 (9) ◽

pp. 245-245

Keyword(s):

Free Atmosphere

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Power spectra of turbulence in the free atmosphere

Tellus ◽

10.1111/j.2153-3490.1967.tb01474.x ◽

1967 ◽

Vol 19 (2) ◽

pp. 206-213 ◽

Cited By ~ 9

Author(s):

N. Z. PINUS ◽

E. R. REITER ◽

G. N. SHUR ◽

N. K. VINNICHENKO

Keyword(s):

Power Spectra ◽

Free Atmosphere

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Observations of Turbulence in Free Atmosphere by Balloon-Borne Sensors

Sensors ◽

10.3390/s18103273 ◽

2018 ◽

Vol 18 (10) ◽

pp. 3273

Author(s):

Lesong Zhou ◽

Zheng Sheng ◽

Qixiang Liao

Keyword(s):

Large Scale ◽

Turbulent Energy ◽

Energy Dissipation Rate ◽

Sensor Data ◽

Free Atmosphere ◽

Height Range ◽

High Latitude Region ◽

Thorpe Scale ◽

Scale Turbulence ◽

Turbulence Parameters

In recent years, Thorpe analysis has been used to retrieve the characteristics of turbulence in free atmosphere from balloon-borne sensor data. However, previous studies have mainly focused on the mid-high latitude region, and this method is still rarely applied at heights above 30 km, especially above 35 km. Therefore, seven sets of upper air (>35 km) sounding data from the Changsha Sounding Station (28°12′ N, 113°05′ E), China are analyzed with Thorpe analysis in this article. It is noted that, in the troposphere, Thorpe analysis can better retrieve the turbulence distribution and the corresponding turbulence parameters. Also, because of the thicker troposphere at low latitudes, the values of the Thorpe scale L T and turbulent energy dissipation rate ε remain greater in a larger height range. In the stratosphere below the height of 35 km, the obtained ε is higher, and Thorpe analysis can only be used to analyze the characteristics of large-scale turbulence. In the stratosphere at a height of 35–40 km, because of the interference of sensor noise, Thorpe analysis can only help to retrieve the rough distribution position of large-scale turbulence, while it can hardly help with the calculation of the turbulence parameters.

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Estimation of the Turbulent Fraction in the Free Atmosphere from MST Radar Measurements

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech1783.1 ◽

2005 ◽

Vol 22 (9) ◽

pp. 1326-1339 ◽

Cited By ~ 13

Author(s):

Richard Wilson ◽

Francis Dalaudier ◽

Francois Bertin

Keyword(s):

Dissipation Rate ◽

Spectral Width ◽

Unbiased Estimation ◽

Small Scale ◽

Doppler Width ◽

Free Atmosphere ◽

Dissipation Rates ◽

Sampling Volume ◽

Radar Measurements ◽

Width Measurements

Abstract Small-scale turbulence in the free atmosphere is known to be intermittent in space and time. The turbulence fraction of the atmosphere is a key parameter in order to evaluate the transport properties of small-scale motions and to interpret clear-air radar measurements as well. Mesosphere–stratosphere–troposphere (MST)/stratosphere–troposphere (ST) radars provide two independent methods for the estimation of energetic parameters of turbulence. First, the Doppler spectral width σ2 is related to the dissipation rate of kinetic energy εk. Second, the radar reflectivity, or C2n, relates to the dissipation rate of available potential energy εp. However, these two measures yield estimates that differ with respect to an important point. The Doppler width measurements, and related εk, are reflectivity-weighted averages. On the other hand, the reflectivity estimate is a volume-averaged quantity. The values of εp depend on both the turbulence intensity and the turbulent fraction within the radar sampling volume. Now, the two dissipation rates εp and εk are related quantities as shown by various measurements within stratified fluids (atmosphere, ocean, lakes, or laboratory). Therefore, by assuming a “canonical” value for the ratio of dissipation rates, an indirect method is proposed to infer the turbulent fraction from simultaneous radar measurements of reflectivity and Doppler broadening within a sampling volume. This method is checked by using very high resolution radar measurements (30 m and 51 s), obtained by the PROUST radar during a field campaign. The method is found to provide an unbiased estimation of the turbulent fraction, within a factor of 2 or less.

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