scholarly journals A Nonlinear Theory of Atmospheric Blocking: A Potential Vorticity Gradient View

2019 ◽  
Vol 76 (8) ◽  
pp. 2399-2427 ◽  
Author(s):  
Dehai Luo ◽  
Wenqi Zhang ◽  
Linhao Zhong ◽  
Aiguo Dai
Keyword(s):  
Zonal Wind ◽  
Potential Vorticity ◽  
Interaction Model ◽  
Energy Dispersion ◽  
Double Peak Structure ◽  
Westerly Jet ◽  
Peak Structure ◽  
Oriented Dipole ◽  
Barotropic Atmosphere ◽  
Multiscale Interaction

Abstract In this paper, an extended nonlinear multiscale interaction model of blocking events in the equivalent barotropic atmosphere is used to investigate the effect of a slowly varying zonal wind in the meridional direction on dipole blocking that is regarded as a nonlinear Rossby wave packet. It is shown that the meridional gradient of potential vorticity (PVy=∂PV/∂y) prior to the blocking onset, which is related to the background zonal wind and its nonuniform meridional shear, can significantly affect the lifetime, intensity, and north–south asymmetry of dipole blocking, while the blocking dipole itself is driven by preexisting incident synoptic-scale eddies. The magnitude of the background PVy determines the energy dispersion and nonlinearity of blocking. It is revealed that a small background PVy is a prerequisite for strong and long-lived eddy-driven blocking that behaves as a persistent meandering westerly jet stream, while the blocking establishment further reduces the PVy within the blocking region, resulting in a positive feedback between blocking and PVy. When the core of the background westerly jet shifts from higher to lower latitudes, the blocking shows a northwest–southeast-oriented dipole with a strong anticyclonic anomaly to the northwest and a weak cyclonic anomaly to the southeast as its northern pole moves westward more rapidly and has weaker energy dispersion and stronger nonlinearity than its southern pole because of the smaller PVy in higher latitudes. The opposite is true when the background jet shifts toward higher latitudes. The asymmetry of dipole blocking vanishes when the background jet shows a symmetric double-peak structure. Thus, a small prior PVy is a favorable precursor for the occurrence of long-lived and large-amplitude blocking.

A Unified Nonlinear Multiscale Interaction Model of Pacific–North American Teleconnection Patterns

2020 ◽  
Vol 77 (4) ◽  
pp. 1387-1414
Author(s):  
Dehai Luo ◽  
Yao Ge ◽  
Wenqi Zhang ◽  
Aiguo Dai
Keyword(s):  
North Atlantic ◽  
North American ◽  
Wave Train ◽  
Interaction Model ◽  
Energy Dispersion ◽  
Pacific North American ◽  
The North ◽  
The North Atlantic ◽  
The Difference ◽  
Multiscale Interaction

Abstract In this paper, reanalysis data are first analyzed to reveal that the individual negative (positive)-phase Pacific–North American pattern (PNA) or PNA− (PNA+) has a lifetime of 10–20 days, is characterized by strong (weak) westerly jet stream meanders, and exhibits clear wave train structures, whereas the PNA− with rapid retrogression tends to have longer lifetime and larger amplitude than the PNA+ with slow retrogression. In contrast, the wave train structure of the North Atlantic Oscillation (NAO) is less distinct, and the positive (negative)-phase NAO shows eastward (westward) movement around a higher latitude than the PNA. Moreover, it is found that the PNA wave train occurs under a larger background meridional potential vorticity gradient (PVy) over the North Pacific than that over the North Atlantic for the NAO. A unified nonlinear multiscale interaction (UNMI) model is then developed to explain why the PNA as a nonlinear wave packet has such characteristics and its large difference from the NAO. The model results reveal that the larger background PVy for the PNA (due to its location at lower latitudes) leads to its larger energy dispersion and weaker nonlinearity than the NAO, thus explaining why the PNA (NAO) is largely a linear (nonlinear) process with a strong (weak) wave train structure, though it is regarded as a nonlinear initial-value problem. The smaller PVy for the PNA− than for the PNA+ leads to lower energy dispersion and stronger nonlinearity for PNA−, which allows it to maintain larger amplitude and have a longer lifetime than the PNA+. Thus, the difference in the background PVy is responsible for the asymmetry between the two phases of PNA and the difference between the PNA and NAO.

scholarly journals A Nonlinear Multiscale Theory of Atmospheric Blocking: Dynamical and Thermodynamic Effects of Meridional Potential Vorticity Gradient

2020 ◽  
Vol 77 (7) ◽  
pp. 2471-2500 ◽  
Author(s):  
Dehai Luo ◽  
Wenqi Zhang
Keyword(s):  
Potential Vorticity ◽  
Large Amplitude ◽  
Three Dimensional ◽  
Interaction Model ◽  
Nonlinear Behavior ◽  
Vertical Variation ◽  
Jet Streams ◽  
Westerly Jet ◽  
Slow Decay ◽  
Long Lifetime

AbstractIn this paper, an extended nonlinear multiscale interaction model is proposed to examine nonlinear behavior of eddy-driven blocking as a Rossby wave packet in a three-dimensional background flow by dividing the background meridional potential vorticity gradient (PVy) into dynamical PVy related to the horizontal (mainly meridional) shear of background westerly wind (BWW) and thermodynamic PVy associated with the meridional temperature gradient (MTG). It is found that eddy-driven baroclinic blocking with large amplitude in the midtroposphere tends to have a longer lifetime (~20 days) in a baroclinic atmosphere with stratification than eddy-driven barotropic blocking without vertical variation (less than 15 days). It is shown that barotropic blocking shows a northwest–southeast orientation and has long lifetime, large retrogression, and slow decay only for weaker barotropic BWW and in higher latitudes. In a baroclinic atmosphere with stratification, baroclinic blocking shows long lifetime, strong eastward movement, slow decay, weak strength, and less local persistence for large barotropic BWW and under , but becomes less slow decay, weak retrogression, and large local persistence for small barotropic BWW and . Such a blocking with a north–south antisymmetric dipole, large amplitude, and long local persistence, characterized by a persistent large meander of westerly jet streams, is easily seen when baroclinic BWW and are small in the lower to midtroposphere. Comparatively, the magnitude of plays a larger role in the blocking change than that of , whereas the vertical variation of MTG is more important for the blocking change than the MTG itself for some cases.

scholarly journals Atomistic investigation of hybrid plasmonic systems

2019 ◽  
Vol 9 ◽  
pp. 184798041985653
Author(s):  
Giulia Giannone ◽  
Fabio Della Sala ◽  
Stefania D’Agostino
Keyword(s):  
Density Functional ◽  
Electromagnetic Interaction ◽  
Near Field ◽  
Interaction Model ◽  
Localized Surface Plasmon ◽  
Tetrahedral Cluster ◽  
Functional Theory ◽  
Double Peak Structure ◽  
Peak Structure ◽  
Transition Densities

By using time-dependent density functional theory, we investigate in a fully quantum mechanical framework the interactions, in an ultra-near-field regime, between a localized surface plasmon excitable in a silver tetrahedral cluster and a molecular exciton with excitation energy in the same range. We show that, for metal–molecule distances below 5 Å, the optical response of the system results characterized by the appearance of a double peak structure. We analyze the transition densities for the resonant energies and propose a plasmon–exciton electromagnetic interaction model to explain the emerging of a lower energy resonance in the spectra of such kind of hybrid systems of interest for molecular plasmonics.

Triply Differential Positron and Electron Impact Ionization of Argon: Systematic Features and Scaling

Atoms ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 78
Author(s):  
R. D. DuBois ◽  
O. G. de Lucio
Keyword(s):  
Momentum Transfer ◽  
Electron Impact ◽  
Impact Ionization ◽  
Emission Angle ◽  
Electron Impact Ionization ◽  
Charge Effects ◽  
Double Peak Structure ◽  
Peak Structure ◽  
Momentum Transfer Range ◽  
Projectile Charge

Triply differential data are presented for the 200 eV positron and electron impact ionization of argon. Six electron emission energies between 2.6 and 19 eV, and for scattering angles of 2, 3, and 4 degrees cover a momentum transfer range of 0.16 to 0.31 a.u. The binary and recoil intensities are fitted using a double peak structure in both regions, which, for the present kinematic conditions, are unresolved. The fitted peak intensities and angular positions are shown to have systematic dependences as a function of the momentum transfer and kinematic emission angle, respectively, and illustrate projectile charge effects. A comparison with available theories is made where it is seen that the most notable differences include the fact that for the binary lobe, the observed intensity for emission angles around 100° is absent in the theories, and the theoretical predications overestimate the importance of recoil interactions.

scholarly journals Differences between coastal and open ocean distributions of N<sub>2</sub>O in the oxygen minimum zone off Peru

2015 ◽  
Vol 12 (13) ◽  
pp. 10167-10193 ◽  
Author(s):  
A. Kock ◽  
D. L. Arévalo-Martínez ◽  
C. R. Löscher ◽  
H. W. Bange
Keyword(s):  
Linear Relationship ◽  
Coastal Upwelling ◽  
Oxygen Minimum Zone ◽  
Open Ocean ◽  
Oxygen Utilization ◽  
Double Peak Structure ◽  
Peak Structure ◽  
Minimum Zone ◽  
Oxygen Minimum ◽  
Oxygen Concentrations

Abstract. Depth profiles of nitrous oxide (N2O) were measured during six cruises to the upwelling area and oxygen minimum zone (OMZ) off Peru in 2009 and 2012/13, covering both the coastal shelf region and the adjacent open ocean. N2O profiles displayed a strong sensitivity towards oxygen concentrations. Open ocean profiles showed a transition from a broad maximum to a double-peak structure towards the centre of the OMZ where the oxygen minimum was more pronounced. Maximum N2O concentrations in the open ocean were about 80 nM. A linear relationship between ΔN2O and apparent oxygen utilization (AOU) could be found for all measurements within the upper oxycline, with a slope similar to studies in other oceanic regions. N2O profiles close to the shelf revealed a much higher variability, with N2O concentrations in the upper oxycline reaching up to several hundred nanomoles per liter at selected stations. Due to the extremely sharp oxygen gradients at the shelf, these maxima occurred in very shallow water depths of less than 50 m. In this area, a linear relationship between ΔN2O and AOU could not be observed. N2O concentrations above 100 nM were observed at oxygen concentrations ranging from close to saturation to suboxic conditions. Our results indicate that the coastal upwelling off Peru at the shelf causes conditions that lead to extreme N2O accumulation.

scholarly journals Observational evidences of the influences of tropospheric subtropical and midlatitude stratospheric westerly jets on the equatorial stratospheric intraseasonal oscillations

2016 ◽  
Author(s):  
G. Karthick Kumar Reddy ◽  
T. K. Ramkumar ◽  
S. Venkatramana Reddy
Keyword(s):  
Zonal Wind ◽  
Lower Atmosphere ◽  
Theoretical Modelling ◽  
Quasi Biennial Oscillation ◽  
Medium Range Weather Forecast ◽  
Westerly Jet ◽  
Longitudinal Sector ◽  
Vertical Propagation ◽  
Biennial Oscillation ◽  
Subtropical Westerly Jet

Abstract. Using six Global Positioning System (GPS) Radio Occultation (RO) satellites (SAC-C, METOP-A and COSMIC/FORMOSAT-3, CNOFS, GRACE and TerraSAR-X) determined height profiles (1–40 km) of atmospheric temperature over the Indian tropical station of Gadanki and the European Center for Medium Range Weather Forecast (ECMWF) Interim Reanalyses (ERA-Interim) zonal wind and temperature data for four years (2009–2012), the present work reports that the tropospheric Subtropical Westerly Jet (SWJ) and the Midlatitude Stratospheric Westerly Jet (MStWJ) play important roles in controlling differently the vertical propagation of tropical Intra Seasonal Oscillations (ISO) with different period bands from the troposphere up to the stratosphere during Northern winters. In the months of December–May (Northern winter to summer, NWTS) of all these years, there is significant 10–20 day and 20–40 day oscillations in the troposphere up to the height of 13 km and above this it reappears at all heights above 21 km. The 40–80 day oscillation also shows similar characteristics except that it almost disappeared during NWTS months of the year 2010–2011 in the stratosphere. The absence of these signals in the intervening heights of ~ 17–20 km is explained on the basis that these two bands actually propagate from the tropical to subtropical region near the tropopause and then reappears in the tropical stratosphere after refracted by the subtropical westerly jet. The poleward and equatorward propagation of these bands in the troposphere and stratosphere respectively are found using the ERA-interim data. Further the two longer period bands of ISO show strong quasi-biennial oscillation in the lower atmosphere with opposite phases (when one band shows maximum the other one shows minimum in a particular year) between these two bands. It is also observed that the phase of the tropical stratospheric Quasi Biennial Oscillation (QBO) has significant control on the strength of the Mid latitude stratospheric westerly jet (MStWJ) that in turn controls the refraction of the tropical tropospheric longer (40–80 days, Longer period ISO; LISO) but not the smaller periods of ISO (SISO) back to the tropical stratosphere. In accordance with earlier theoretical modelling studies, the westerly phase of the lower stratospheric QBO occurred during NWTS months of 2010–2011 over the Indian longitudinal sector causes severe disruption of the MStWJ at 30 km height. This disruption caused the prevention of refraction back again to the tropical stratosphere of significant tropospheric LISO that arrived from the tropics through the tropopause. Further, in these four years, it is observed no direct vertical propagation of tropical tropospheric ISO to the stratosphere. The interannual variations in the tropical stratospheric LISO are related strongly to the phase of the equatorial lower stratospheric QBO in zonal wind and the strength of the MStWJ.

scholarly journals The Role of Land–Sea Topography in Blocking Formation in a Block–Eddy Interaction Model

2006 ◽  
Vol 63 (11) ◽  
pp. 3056-3065 ◽  
Author(s):  
Dehai Luo ◽  
Zhe Chen
Keyword(s):  
Large Scale ◽  
Theoretical Study ◽  
Interaction Model ◽  
Synoptic Scale ◽  
Westerly Jet ◽  
Blocking High ◽  
Dipole Component ◽  
Large Scale Land ◽  
Northern And Southern Hemispheres

Abstract This paper is an extension of a theoretical study by Luo on the effect of large-scale land–sea contrast (LSC) topography on the formation of an eddy-driven blocking. It is found that the topography term can be included explicitly in the blocking evolution equation because of the inclusion of the higher-order wave–topography interaction. Although the blocking flow cannot be excited purely by the LSC topography, the LSC topography is found to be capable of enhancing the amplification of the dipole component in a blocking flow associated with upstream synoptic-scale eddies. In this case, a strong omega-type blocking high can be driven by the joint action of synoptic-scale eddies and LSC topography. This seems to provide an explanation of a difference in blocking intensity between the Northern and Southern Hemispheres. The most important finding of this paper is that in the presence of LSC topography the double jets that appear during the onset of an eddy-driven dipole block collapse into a strong single westerly jet that is within the south side of an omega-type blocking high, which is different from the result predicted by the theoretical model proposed in Luo’s previous work.

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