scholarly journals The budget of local available potential energy of low-frequency eddies in Northern Hemispheric winter

2020 ◽  
pp. 1-46
Author(s):  
Xianglin Dai ◽  
Yang Zhang ◽  
Xiu-Qun Yang
Keyword(s):  
Potential Energy ◽  
Energy Budget ◽  
High Frequency ◽  
Large Scale ◽  
Vertical Structure ◽  
Low Frequency ◽  
Available Potential Energy ◽  
Background Temperature ◽  
Northern Hemispheric ◽  
Climate Events

AbstractLow-frequency (LF) transient eddies (intra-seasonal eddies with time scales longer than 10 days) is increasingly found important in large-scale atmospheric circulations, high-impact climate events and subseasonal-to-seasonal forecast. In this study, features and the maintenance of available potential energy of LF eddies (LF EAPE), which denotes LF temperature fluctuations, have been investigated. Our study shows that wintertime LF EAPE, with greater amplitude than that of the extensively studied high-frequency (HF) eddies, exhibits distinct horizontal and vertical structures. Different from HF eddies, whose action centers are over midlatitude oceans, the LF EAPE is most active in the continents in midlatitude, as well as the subpolar region with shallower vertical structure. By diagnosing the derived energy budget of LF EAPE, we find that, with the strong background temperature gradient in mid- and high-latitude continents (e.g. coast regions along Greenland-Barents-Kara sea), baroclinic generation is the major source of LF EAPE. The generated LF EAPE in the subpolar region is transported downstream and southward to midlatitude continents via background flow. The generated LF EAPE is also dissipated by HF eddies, damped by diabatic effect and converted to LF EKE via vertical motions. The above energy budget, together with the barotropic dynamics revealed by previousworks, suggests multiple energy sources thus complicated dynamics of LF variabilities.

scholarly journals Optimizing the Frequency Capping: A Robust and Reliable Methodology to Define the Number of Ads to Maximize ROAS

2021 ◽  
Vol 11 (15) ◽  
pp. 6688
Author(s):  
Jesús Romero Leguina ◽  
Ángel Cuevas Rumin ◽  
Rubén Cuevas Rumin
Keyword(s):  
High Frequency ◽  
Large Scale ◽  
Low Frequency ◽  
Digital Marketing ◽  
Optimal Frequency ◽  
Novel Technique ◽  
Maximum Threshold

The goal of digital marketing is to connect advertisers with users that are interested in their products. This means serving ads to users, and it could lead to a user receiving hundreds of impressions of the same ad. Consequently, advertisers can define a maximum threshold to the number of impressions a user can receive, referred to as Frequency Cap. However, low frequency caps mean many users are not engaging with the advertiser. By contrast, with high frequency caps, users may receive many ads leading to annoyance and wasting budget. We build a robust and reliable methodology to define the number of ads that should be delivered to different users to maximize the ROAS and reduce the possibility that users get annoyed with the ads’ brand. The methodology uses a novel technique to find the optimal frequency capping based on the number of non-clicked impressions rather than the traditional number of received impressions. This methodology is validated using simulations and large-scale datasets obtained from real ad campaigns data. To sum up, our work proves that it is feasible to address the frequency capping optimization as a business problem, and we provide a framework that can be used to configure efficient frequency capping values.

Investigating Thunderstorm HF/VHF Radio Bursts with Weak Lower Frequency Radiation

2020 ◽  
Author(s):  
Ningyu Liu ◽  
Joseph Dwyer
Keyword(s):  
High Frequency ◽  
Large Scale ◽  
Strong Field ◽  
Large Fraction ◽  
Low Frequency ◽  
Very High Frequency ◽  
Lightning Initiation ◽  
Study Support ◽  
Volcanic Lightning ◽  
Frequency Radiation

<p>While the spectrum of lightning electromagnetic radiation is known to peak around 5-10 kHz in the very low frequency (VLF) range, intense high frequency/very high frequency (HF/VHF) radiation can be produced by various lightning related processes. In fact, thunderstorm narrow bipolar events (NBEs), which are capable of initiating lightning, are the most powerful HF/VHF sources in nature on Earth. But even for NBEs, the spectral intensity in HF/VHF is still many orders of magnitude weaker than that of lower frequencies (Liu et al., JGR, 124, https://doi.org/10.1029/2019JD030439, 2019). HF/VHF bursts with weak VLF signals, however, can also be produced by thunderstorms. These bursts may be related to the thunderstorm precursor events noted by Rison et al. (Nat. Commun., 7, 10721, 2016) and are also found to precede a large fraction of lightning initiation (Lyu et al., JGR, 124, 2994, 2019). They are also known as continual radio frequency (CRF) radiation associated with volcanic lightning (Behnke et. al., JGR, 123, 4157, 2018).</p><p> </p><p>In this talk, we report a theoretical and modeling study to investigate a physical mechanism for production of those HF/VHF bursts. The study is built on the theory developed recently concerning the radio emissions from an ensemble of streamers (Liu et al., 2019). We find an ensemble of streamer discharges that develop in random directions can produce HF/VHF radiation with intensity comparable to those all developing in a single direction, but the VLF intensity is many orders of magnitude weaker. The results of our study support the conclusions of Behnke et. al (2018) that CRF is produced in the absence of large-scale electric field, it results in insignificant charge transfer, and it is caused by streamers. In the context of the HF/VHF bursts preceding lightning initiation (Lyu et. al, 2019), our results imply that highly localized strong field regions exist in thunderstorms and streamers take place in those regions, which somehow precondition the medium for lightning initiation.</p>

scholarly journals Applications of a Moist Nonhydrostatic Formulation of the Spectral Energy Budget to Baroclinic Waves. Part I: The Lower-Stratospheric Energy Spectra

2015 ◽  
Vol 72 (5) ◽  
pp. 2090-2108 ◽  
Author(s):  
Jun Peng ◽  
Lifeng Zhang ◽  
Jiping Guan
Keyword(s):  
Kinetic Energy ◽  
Potential Energy ◽  
Energy Budget ◽  
Vertical Flux ◽  
Energy Spectra ◽  
Spectral Energy ◽  
Positive Contribution ◽  
Flux Divergence ◽  
Available Potential Energy ◽  
Baroclinic Waves

Abstract The authors investigate the mesoscale dynamics that produce the lower-stratospheric energy spectra in idealized moist baroclinic waves, using the moist nonhydrostatic formulation of spectral energy budget of kinetic energy and available potential energy by J. Peng et al. The inclusion of moist processes energizes the lower-stratospheric mesoscale, helping to close the gap between observed and simulated energy spectra. In dry baroclinic waves, the lower-stratospheric mesoscale is mainly forced by weak downscale cascades of both horizontal kinetic energy (HKE) and available potential energy (APE) and by a weak conversion of APE to HKE. At wavelengths less than 1000 km, the pressure vertical flux divergence also has a significant positive contribution to the HKE; however, this positive contribution is largely counteracted by the negative HKE vertical flux divergence. In moist baroclinic waves, the lower-stratospheric mesoscale HKE is mainly generated by the pressure and HKE vertical flux divergences. This additional HKE is partly converted to APE and partly removed by diffusion. Another negative contribution to the mesoscale HKE is from the forcing of a visible upscale HKE cascade. Besides the conversion of HKE, however, the three-dimensional divergence also has a significant positive contribution to the mesoscale APE. With these two direct APE sources, the lower-stratospheric mesoscale also undergoes a much stronger upscale APE cascade. These results suggest that both downscale and upscale cascades through the mesoscale are permitted in the real atmosphere and the direct forcing of the mesoscale is available to feed the upscale energy cascade.

scholarly journals Drag forces on a bed particle in open-channel flow: effects of pressure spatial fluctuations and very-large-scale motions

2019 ◽  
Vol 863 ◽  
pp. 494-512 ◽  
Author(s):  
S. M. Cameron ◽  
V. I. Nikora ◽  
I. Marusic
Keyword(s):  
Channel Flow ◽  
Drag Force ◽  
High Frequency ◽  
Large Scale ◽  
Open Channel ◽  
Low Frequency ◽  
Open Channel Flow ◽  
Stereoscopic Particle Image Velocimetry ◽  
Force Fluctuations ◽  
Drag Forces

The fluctuating drag forces acting on spherical roughness elements comprising the bed of an open-channel flow have been recorded along with synchronous measurements of the surrounding velocity field using stereoscopic particle image velocimetry. The protrusion of the target particle, equipped with a force sensor, was systematically varied between zero and one-half diameter relative to the hexagonally packed adjacent spheres. Premultiplied spectra of drag force fluctuations were found to have bimodal shapes with a low-frequency (${\approx}0.5~\text{Hz}$) peak corresponding to the presence of very-large-scale motions (VLSMs) in the turbulent flow. The high-frequency ($\gtrapprox 4~\text{Hz}$) region of the drag force spectra cannot be explained by velocity time series extracted from points around the particle, but instead appears to be dominated by the action of pressure gradients in the overlying flow field. For small particle protrusions, this high-frequency region contributes a majority of the drag force variance, while the relative importance of the low-frequency drag force fluctuations increases with increasing protrusion. The amplitude of high-frequency drag force fluctuations is modulated by the VLSMs irrespective of particle protrusion. These results provide some insight into the mechanics of bed particle stability and indicate that the optimum conditions for particle entrainment may occur when a low-pressure region embedded in the high-velocity portion of a VLSM overlays a particle.

scholarly journals The Effect of Vertical Baroclinicity Concentration on Atmospheric Macroturbulence Scaling Relations

2017 ◽  
Vol 74 (5) ◽  
pp. 1651-1667 ◽  
Author(s):  
Janni Yuval ◽  
Yohai Kaspi
Keyword(s):  
Relaxation Time ◽  
Temperature Gradient ◽  
Potential Energy ◽  
Vertical Structure ◽  
Temperature Gradients ◽  
Lapse Rate ◽  
Meridional Temperature Gradient ◽  
Available Potential Energy ◽  
The Mean ◽  
Mean State

Abstract Motivated by the expectation that under global warming upper-level meridional temperature gradients will increase while lower-level temperature gradients will decrease, the relations between the vertical structure of baroclinicity and eddy fields are investigated. The sensitivity of eddies and the relation between the mean available potential energy and eddy quantities are studied for cases where the vertical structure of the lapse rate and meridional temperature gradient are modified. To investigate this systematically, an idealized general circulation model with a Newtonian cooling scheme that has a very short relaxation time for the mean state and a long relaxation time for eddies is used. This scheme allows for any chosen zonally mean state to be obtained with good precision. The results indicate that for similar change in the lapse rate or meridional temperature gradient, eddies are more sensitive to changes in baroclinicity where it is already large. Furthermore, when the vertical structure of the lapse rate or the meridional temperature gradient is modified, there is no universal linear relation between the mean available potential energy and eddy quantities.

scholarly journals Contributions of Individual Atmospheric Diabatic Heating Processes to the Generation of Available Potential Energy

2013 ◽  
Vol 26 (12) ◽  
pp. 4244-4263 ◽  
Author(s):  
Joy Romanski ◽  
William B. Rossow
Keyword(s):  
Potential Energy ◽  
Large Scale ◽  
Diabatic Heating ◽  
Temporal Distribution ◽  
Heat Fluxes ◽  
Radiative Fluxes ◽  
Available Potential Energy ◽  
Summer Hemisphere ◽  
Order Of Magnitude ◽  
The Individual

Abstract The generation of zonal and eddy available potential energy (Gz and Ge) as formulated by Lorenz are computed on a global-, daily-, and synoptic-scale basis to consider the contribution of each diabatic heating component separately and in combination. Using global, mostly satellite-derived datasets for the diabatic heating components and the temperature enables us to obtain Gz and, especially, Ge from observations for the first time and at higher temporal and spatial resolution than previously possible. The role of clouds in maintaining G is investigated. The global annual mean Gz is 1.52 W m−2. Values reach a minimum of 0.63 W m−2 in the Northern Hemisphere during spring and a maximum of 2.27 W m−2 in the Southern Hemisphere during winter. The largest contributors to Gz are latent heating in the tropical upper troposphere, associated with the intertropical convergence zone in the summer hemisphere and surface sensible heat fluxes in the winter pole. Diabatic cooling by radiative fluxes (mostly longwave) generally destroys Gz. The value of Ge is negative and is about an order of magnitude smaller than Gz, with a global annual mean of −0.29 W m−2. However, the small value of Ge results from the cancellation of the contributions from the individual diabatic heating terms, which are actually roughly similar in magnitude to their Gz contributions. The results presented herein suggest that the large-scale dynamics of the atmosphere organize the spatial and temporal distribution of clouds and precipitation in such a way as to increase the energy available to drive the circulation, a kind of positive feedback.

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