scholarly journals Diurnal differences in tropical anvil cloud evolution

2021 ◽  
Author(s):  
Blaž Gasparini ◽  
Adam B. Sokol ◽  
Casey J. Wall ◽  
Dennis L. Hartmann ◽  
Peter N. Blossey
Keyword(s):  
Cloud Evolution

scholarly journals Efficiency of thermal conduction in a magnetized circumgalactic medium

2021 ◽  
Vol 502 (1) ◽  
pp. 1263-1278
Author(s):  
Richard Kooij ◽  
Asger Grønnow ◽  
Filippo Fraternali
Keyword(s):  
Magnetic Field ◽  
Thermal Conduction ◽  
Large Temperature ◽  
Gas Condensation ◽  
Circumgalactic Medium ◽  
Field Lines ◽  
Gas Accretion ◽  
Cloud Evolution ◽  
The Magnetic Field ◽  
Cold Gas

ABSTRACT The large temperature difference between cold gas clouds around galaxies and the hot haloes that they are moving through suggests that thermal conduction could play an important role in the circumgalactic medium. However, thermal conduction in the presence of a magnetic field is highly anisotropic, being strongly suppressed in the direction perpendicular to the magnetic field lines. This is commonly modelled by using a simple prescription that assumes that thermal conduction is isotropic at a certain efficiency f < 1, but its precise value is largely unconstrained. We investigate the efficiency of thermal conduction by comparing the evolution of 3D hydrodynamical (HD) simulations of cold clouds moving through a hot medium, using artificially suppressed isotropic thermal conduction (with f), against 3D magnetohydrodynamical (MHD) simulations with (true) anisotropic thermal conduction. Our main diagnostic is the time evolution of the amount of cold gas in conditions representative of the lower (close to the disc) circumgalactic medium of a Milky-Way-like galaxy. We find that in almost every HD and MHD run, the amount of cold gas increases with time, indicating that hot gas condensation is an important phenomenon that can contribute to gas accretion on to galaxies. For the most realistic orientations of the magnetic field with respect to the cloud motion we find that f is in the range 0.03–0.15. Thermal conduction is thus always highly suppressed, but its effect on the cloud evolution is generally not negligible.

Three-dimensional computer simulation of plasma cloud evolution in the ionosphere

1990 ◽  
Vol 38 (11) ◽  
pp. 1375-1386 ◽  
Author(s):  
V.A. Rozhansky ◽  
I.Yu. Veselova ◽  
S.P. Voskoboynikov
Keyword(s):  
Computer Simulation ◽  
Three Dimensional ◽  
Plasma Cloud ◽  
Cloud Evolution

scholarly journals Polar Stratospheric Cloud evolution and chlorine activation measured by CALIPSO and MLS, and modelled by ATLAS

2015 ◽  
Vol 15 (16) ◽  
pp. 22141-22182
Author(s):  
H. Nakajima ◽  
I. Wohltmann ◽  
T. Wegner ◽  
M. Takeda ◽  
M. C. Pitts ◽  
...  
Keyword(s):  
The Arctic ◽  
Temperature History ◽  
Threshold Temperature ◽  
Limiting Factor ◽  
Temperature Decrease ◽  
Air Mass ◽  
Frost Point ◽  
Rapid Temperature ◽  
Cloud Evolution ◽  
Stratospheric Clouds

Abstract. We examined observations of polar stratospheric clouds (PSCs) by CALIPSO and of HCl, ClO and HNO3 by MLS along air mass trajectories to investigate the dependence of the inferred PSC composition on the temperature history of the air parcels, and the dependence of the level of chlorine activation on PSC composition. Several case studies based on individual trajectories from the Arctic winter 2009/10 were conducted, with the trajectories chosen such that the first processing of the air mass by PSCs in this winter occurred on the trajectory. Transitions of PSC composition classes were observed to be highly dependent on the temperature history. In cases of a gradual temperature decrease, nitric acid trihydrate (NAT) and super-cooled ternary solution (STS) mixture clouds were observed. In cases of rapid temperature decrease, STS clouds were first observed, followed by NAT/STS mixture clouds. When temperatures dropped below the frost point, ice clouds formed, and then transformed into NAT/STS mixture clouds when temperature increased above the frost point. The threshold temperature for rapid chlorine activation on PSCs is approximately 4 K below the NAT existence temperature, TNAT. Furthermore, simulations of the ATLAS chemistry and transport box model along the trajectories were used to corroborate the measurements and show good agreement with the observations. Rapid chlorine activation was observed when an airmass encountered PSCs. The observed and modelled dependence of the rate of chlorine activation on the PSC composition class was small. Usually, chlorine activation was limited by the amount of available ClONO2. Where ClONO2 was not the limiting factor, a large dependence on temperature was evident.

scholarly journals Exploring Expansion and Innovations in Cloud Computing

2019 ◽  
Vol 1 (1) ◽  
pp. 46-59
Author(s):  
Jitendra Singh
Keyword(s):  
Information Technology ◽  
Cloud Computing ◽  
Cloud Services ◽  
Recent Past ◽  
Cloud Development ◽  
User Expectations ◽  
Cloud Evolution ◽  
The Impact

Cloud computing is one of the highly sought-after paradigms in information technology. In several cases, it has surpassed earlier predictions of growth, and expanding its services to cover all the key areas. With the growing usage of the cloud, new requirements have also surfaced. To meet user expectations, the cloud services pool has expanded drastically. In order to meet the subscriber's futuristic demands, cloud computing needs to advance further. This work undertakes the study of expansion and innovations that have already happened in the recent past. In addition, perceived cloud evolution in the futuristic cloud has been presented. During the course of exploration, the impact of hardware and software on evolution has been taken into account. Considering the benefits involved, and the current advancement, this work concludes by presenting the innovations that will lead to cloud development.

Beobachtung von Windprofilen mittels Wolkenradar und Dopplerlidar 

2021 ◽  
Author(s):  
Bernhard Pospichal ◽  
Marcus Müller ◽  
Stefan Kneifel
Keyword(s):  
Research Infrastructure ◽  
Trace Gas ◽  
Aerosol Cloud ◽  
Cloud Evolution

<p>Die Messung des 3D-Windprofils erfordert – abgesehen von in-situ Messungen – ein aktives Fernerkundungsverfahren (meist Radar oder Lidar), welches mit geneigten Strahlen unter verschiedenen, mindestens drei Azimutwinkeln Pulse ausstrahlt („Doppler beam swinging“). Aus den gemessenen Doppler-Radialgeschwindigkeiten entlang der Strahlen kann dann das dreidimensionale Windfeld abgeleitet werden. Dies ist nur möglich, sofern Partikel vorhanden sind, die bei der gegebenen Wellenlänge ein Rückstreusignal erzeugen.</p> <p>Bereits seit mehreren Jahrzehnten sind Radar-Windprofiler im Einsatz, die bei Wellenlängen zwischen 50 und 1000 MHz arbeiten und mittels Bragg-Streuung an Fluktuationen des Brechungsindex ein Rückstreusignal erhalten. Durch die lange Wellenlänge sind große Antennen erforderlich, was dazu führt, dass die Geräte nicht flexibel einsetzbar sind.</p> <p>Innerhalb des Netzwerks der europäischen Forschungsinfrastruktur ACTRIS (Aerosol, Cloud and Trace Gas Research Infrastructure) sind mehrere Standorte für Wolkenbeobachtungen mit einem scannenden Wolkenradar und einem Doppler-Windlidar ausgestattet, die auch zur Beobachtung von Windprofilen in der Troposphäre herangezogen werden können. Diese Messgeräte ergänzen sich, da das Lidar besonders in der Grenzschicht bzw. unterhalb von Wolken messen kann. Das Wolkenradar hingegen liefert Signale hauptsächlich aus Wolkenschichten, von welchen das Lidar aufgrund der starken Extinktion der Strahlung in Wolken keine Information erhält. Zusätzlich können beim Wolkenradar in der warmen Jahreszeit auch Insekten als Tracer verwendet werden, die häufig bis in Höhen von 3-4 km beobachtet werden können. </p> <p>Diese Präsentation zeigt anhand von Beobachtungen über mehr als zwei Jahre an der Messplattform JOYCE (Jülich Observatory for Cloud Evolution) eine neue Methode zur Kombination der Windprofile aus Wolkenradar und Lidar. Neben einer Betrachtung der Genauigkeit, sowie möglicher Fehlerquellen, werden auch die generellen Bedingungen für die Anwendung der Methode diskutiert. Es werden Anwendungsbeispiele gezeigt, wie diese kombinierten Windprofile zur Validierung von Satellitenbeobachtungen (z.B. Aeolus) oder zur Evaluation von atmosphärischen Modellen genutzt werden können. </p> <p> </p>

scholarly journals Normalized Hail Particle Size Distributions from the T-28 Storm-Penetrating Aircraft

2019 ◽  
Vol 58 (2) ◽  
pp. 231-245 ◽  
Author(s):  
Paul R. Field ◽  
Andrew J. Heymsfield ◽  
Andrew G. Detwiler ◽  
Jonathan M. Wilkinson
Keyword(s):  
Particle Size ◽  
Water Content ◽  
Size Distribution ◽  
Optical Probe ◽  
Particle Size Distributions ◽  
South Dakota School ◽  
Significant Damage ◽  
In Situ Observations ◽  
Cloud Evolution

AbstractHail and graupel are linked to lightning production and are important components of cloud evolution. Hail can also cause significant damage when it precipitates to the surface. The accurate prediction of the amount and location of hail and graupel and the effects on the other hydrometeor species depends upon the size distribution assumed. Here, we use ~310 km of in situ observations from flights of the South Dakota School of Mines and Technology T-28 storm-penetrating aircraft to constrain the representation of the particle size distribution (PSD) of hail. The maximum ~1-km hail water content encountered was 9 g m−3. Optical probe PSD measurements are normalized using two-moment normalization relations to obtain an underlying exponential shape. By linking the two normalizing moments through a power law, a parameterization of the hail PSD is provided based on the hail water content only. Preliminary numerical weather simulations indicate that the new parameterization produces increased radar reflectivity relative to commonly used PSD representations.

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