scholarly journals Targeting Studies for the Extratropical Transition of Hurricane Fabian: Signal Propagation, the Interaction between Fabian and Midlatitude Flow, and an Observation Strategy

2010 ◽  
Vol 138 (8) ◽  
pp. 3224-3242 ◽  
Author(s):  
Hua Chen ◽  
Weiyu Pan
Keyword(s):  
Potential Vorticity ◽  
Lower Troposphere ◽  
Signal Propagation ◽  
Synoptic Situation ◽  
Energy Dispersion ◽  
Extratropical Transition ◽  
Initial Errors ◽  
Targeted Observations ◽  
Upper Level ◽  
The Impact

Abstract This study examines how the impact of targeted observations propagates during the extratropical transition (ET) of Hurricane Fabian. Signal (i.e., the forecast difference between denial experiments and the control experiment) propagation can reveal the interaction between the tropical cyclone (TC) and the midlatitude jet, and the energy dispersion or propagation of the TC undergoing ET also can be determined. The crucial role of an upper-level trough is discussed. Based on this study, a strategy issue regarding targeted observations of ET and several typical problems regarding the numerical prediction of ET are discussed. The results show that the greatest signals along with their propagation are associated closely with various types of instabilities. In general, the signal first appears at the location of the TC, and then it propagates to the midlatitude jet through the interaction between the TC and the jet itself. Thereafter, signals propagate downstream along the jet and downward to the lower troposphere at the same time by way of Rossby wave packets; the jet essentially acts as a waveguide. Through the signal propagation and development in the jet, the impact of targeted observations seems sensitive to the ET process. The interaction between the TC and the jet occurs as high θ (low potential vorticity) air flows out of the TC toward the northeast and into the jet below the tropopause. The interaction may be strengthened by an upstream trough at upper levels. The TC outflow enhances the potential vorticity (PV) gradient and baroclinity in the jet. Therefore, the jet becomes stronger and more baroclinically unstable. The signal propagation also indicates the energy dispersion of a TC undergoing ET. The strong southwesterly flow ahead of the upper-level trough steers Fabian to higher latitudes, and strengthens the advection process of low PV air into the jet. Therefore, the development of the upper-level trough and its proximity to the TC are crucial for the interaction between the TC and the jet, and the resulting signal propagation. Small deviations from this synoptic situation may result in great differences in the signal propagation and the ET forecast. The most suitable region for targeting is likely a region where crucial synoptic processes can magnify initial errors.

The Comparison Study of Targeting Observation for Extratropical Transition of Hurricane Fabian

2012 ◽  
Vol 518-523 ◽  
pp. 5840-5845
Author(s):  
Hua Chen ◽  
Xue Ting Zhang
Keyword(s):  
Positive Impact ◽  
Signal Propagation ◽  
Comparison Study ◽  
Extratropical Transition ◽  
Random Experiment ◽  
Targeted Observations ◽  
Propagation Methods ◽  
And Control ◽  
The Impact ◽  
Sensitive Experiment

This study compares the propagation methods of the impact of targeted observations during the extratropical transition (ET) of Hurricane Fabian in three denial experiments. In sensitive experiment, the signal (forecast difference between denial experiments and control) propagates from the tropical cyclone (TC) to the midlatitude jet through the interaction between the TC and the jet itself. Thereafter, signals propagate eastward along the jet by way of Rossby wave packets. Some differences exist between random/Atlantic and sensitive experiment although many of their signal propagation characteristics are similar. The signal in random experiment is the weakest, and that in Atlantic experiment is the strongest. In Atlantic experiment, initial signals appear not only in Fabian, but also in other regions. In some cases, signals even do not appear in Fabian. Its propagation method is similar to that in sensitive and random experiment except some signals exist at ridges occasionally. From the discussion above, we conclude that targeted observations have more positive impact than random observations, but can not replace observations taken in the whole Atlantic.

scholarly journals Potential Vorticity Diagnosis of the Severe Convective Regime. Part II: The Impact of Idealized PV Anomalies

2008 ◽  
Vol 136 (5) ◽  
pp. 1582-1592 ◽  
Author(s):  
John W. Nielsen-Gammon ◽  
David A. Gold
Keyword(s):  
Potential Vorticity ◽  
Severe Weather ◽  
Jet Stream ◽  
Balance Equations ◽  
Upper Level ◽  
Height Fields ◽  
Upper Level Jet ◽  
The Impact ◽  
Analysis Errors ◽  
Pv Gradient

Abstract Idealized numerical experiments are conducted to understand the effect of upper-tropospheric potential vorticity (PV) anomalies on an environment conducive to severe weather. Anomalies are specified as a single isolated vortex, a string of vortices analogous to a negatively tilted trough, and a pair of string vortices analogous to a position error in a negatively tilted trough. The anomalies are placed adjacent to the tropopause along a strong upper-level jet at a time just prior to a major tornado outbreak and inverted using the nonlinear balance equations. In addition to the expected destabilization beneath and adjacent to a cyclonic PV anomaly, the spatial pattern of the inverted balanced streamfunction and height fields is distorted by the presence of the horizontal PV gradient along the upper-tropospheric jet stream. Streamfunction anomalies are elongated in the cross-jet direction, while height and temperature anomalies are elongated in the along-jet direction. The amplitude of the inverted fields, as well as the changes in CAPE associated with the inverted temperature perturbations, are linearly proportional to the amplitudes of the PV anomalies themselves, and the responses to complex PV perturbation structures are approximated by the sum of the responses to individual simple PV anomalies. This is true for the range of PV amplitudes tested, which was designed to mimic typical 6-h forecast or analysis errors and produced changes in CAPE beneath the trough of well over 100 J kg−1. Impacts on inverted fields are largest when the PV anomaly is on the anticyclonic shear side of the jet, where background PV is small, compared with the cyclonic shear side of the jet, where background PV is large.

scholarly journals High resolution numerical study of the Algiers 2001 flash flood: sensitivity to the upper-level potential vorticity anomaly

2006 ◽  
Vol 7 ◽  
pp. 251-257 ◽  
Author(s):  
S. Argence ◽  
D. Lambert ◽  
E. Richard ◽  
N. Söhne ◽  
J.-P. Chaboureau ◽  
...  
Keyword(s):  
Potential Vorticity ◽  
Flash Flood ◽  
Numerical Study ◽  
Western Mediterranean ◽  
Precipitation Forecast ◽  
Inversion Method ◽  
Strong Impact ◽  
Upper Level ◽  
Vorticity Anomaly ◽  
The Impact

Abstract. From 9 to 11 November 2001, intense cyclogenesis affected the northern coasts of Africa and more particularly the densely populated city of Algiers. During the morning of 10 November, more than 130 mm of precipitation was recorded at Bouzareah and resulted in mudslides which devastated the Bab-el-Oued district. This disaster caused more than 700 casualties and catastrophic damage. Like many other heavy rainstorms in the western Mediterranean, this event was associated with the presence of an upper-level trough materialized by a deep stratospheric intrusion and characterized by high potential vorticity values. In this study, the impact of this synoptic structure on the localization and intensity of the precipitation which affected Algiers is investigated using a potential vorticity (PV) inversion method coupled for the first time with the French non-hydrostatic MESO-NH model. A set of perturbed synoptic environments was designed by slightly modifying the extent and the intensity of the coherent potential vorticity structures in the operational ARPEGE analysis. It is shown that such modifications may have a strong impact on the fine-scale precipitation forecast in the Algiers region, thereby demonstrating the fundamental role played by the potential vorticity anomaly during this exceptional meteorological event.

scholarly journals Connections between Potential Vorticity Intrusions and Convection in the Eastern Tropical Pacific

2008 ◽  
Vol 65 (3) ◽  
pp. 987-1002 ◽  
Author(s):  
Beatriz M. Funatsu ◽  
Darryn W. Waugh
Keyword(s):  
Potential Vorticity ◽  
Mesoscale Model ◽  
Dominant Role ◽  
Deep Convection ◽  
Convective Available Potential Energy ◽  
Lower Troposphere ◽  
Leading Edge ◽  
Upward Motion ◽  
Tropical Eastern Pacific ◽  
Upper Level

Abstract The connections between intrusions of stratospheric air into the upper troposphere and deep convection in the tropical eastern Pacific are examined using a combination of data analysis, potential vorticity (PV) inversion, and numerical simulations. Analysis of NCEP–NCAR reanalyses and satellite measurements of outgoing longwave radiation during intrusion events shows increased cloudiness, lower static stability, upward motion, and a buildup of convective available potential energy (CAPE) at the leading edge of the intruding tongue of high PV. Potential inversion inversion calculations show that the upper-level PV makes the dominant contribution to the changes in the quantities that characterize convection. This supports the hypothesis that upper-level PV anomalies initiate and support convection by destabilizing the lower troposphere and causing upward motion ahead on the PV tongue. The dominant role of the upper-level PV is confirmed by simulations using the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5). Convection only occurs when the upper-level PV anomaly is present in the simulations, and the relative contribution of the upper-level PV to changes in the quantities that characterize convection is similar to that inferred from the PV inversion calculations.

Balanced Response of an Axisymmetric Tropical Cyclone to Periodic Diurnal Heating

2017 ◽  
Vol 74 (10) ◽  
pp. 3325-3337 ◽  
Author(s):  
Erika L. Navarro ◽  
Gregory J. Hakim ◽  
Hugh E. Willoughby
Keyword(s):  
Diurnal Cycle ◽  
Lower Troposphere ◽  
Radiative Heating ◽  
Wind Fields ◽  
Periodic Heating ◽  
Dynamical Mechanism ◽  
Axisymmetric Solution ◽  
Upper Level ◽  
Comparison Of The Results ◽  
The Impact

Abstract A modified version of the Sawyer–Eliassen equation is applied to determine the impact of periodic diurnal heating on a balanced vortex. The TC diurnal cycle is a coherent signal that arises in the cirrus canopy. However, despite thorough documentation in the literature, the dynamical mechanism remains unknown. Recent work demonstrates that periodic radiative heating in the TC outflow layer is linked with an anomalous upper-level circulation; this heating is also associated with a cycle of latent heating in the lower troposphere that corresponds to a cycle in storm intensity. Using a method that is analogous to the Sawyer–Eliassen equation, but for solutions having the same time scale as time-periodic forcing, these distributions are analyzed to determine the effect of periodic diurnal heating on an axisymmetric vortex. Results for periodic heating in the lower troposphere show an overturning circulation that resembles the Sawyer–Eliassen solution. The model simulates positive perturbations in the azimuthal wind field of 2.5 m s−1 near the radius of maximum wind. Periodic heating near the top of the vortex produces a local overturning response in the region of heating and an inertia–buoyancy wave response in the storm environment. Comparison of the results from the modified Sawyer–Eliassen equation to those of an idealized axisymmetric solution for both heating distributions shows similarities in the structure of the perturbation wind fields, suggesting that the axisymmetric TC diurnal cycle is primarily a balanced response driven by periodic heating.

The efficiency of application of virtual cross-sections method and hypotheses MELS in problems of wave signal propagation in elastic waveguides with rough surfaces

2016 ◽  
pp. 3564-3575 ◽  
Author(s):  
Ara Sergey Avetisyan
Keyword(s):  
Half Space ◽  
Cross Sections ◽  
Classical Method ◽  
Signal Propagation ◽  
Elastic Half Space ◽  
Layered Systems ◽  
Surface Layers ◽  
Inhomogeneous Surface ◽  
Wave Signal ◽  
The Impact

The efficiency of virtual cross sections method and MELS (Magneto Elastic Layered Systems) hypotheses application is shown on model problem about distribution of wave field in thin surface layers of waveguide when plane wave signal is propagating in it. The impact of surface non-smoothness on characteristics of propagation of high-frequency horizontally polarized wave signal in isotropic elastic half-space is studied. It is shown that the non-smoothness leads to strong distortion of the wave signal over the waveguide thickness and along wave signal propagation direction as well.  Numerical comparative analysis of change in amplitude and phase characteristics of obtained wave fields against roughness of weakly inhomogeneous surface of homogeneous elastic half-space surface is done by classical method and by proposed approach for different kind of non-smoothness.

scholarly journals Interannual Variability and Trends in Sea Surface Temperature, Lower and Middle Atmosphere Temperature at Different Latitudes for 1980–2019

Atmosphere ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 454
Author(s):  
Andrew R. Jakovlev ◽  
Sergei P. Smyshlyaev ◽  
Vener Y. Galin
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Lower Stratosphere ◽  
Middle Atmosphere ◽  
Southern Oscillation ◽  
Lower Troposphere ◽  
Reanalysis Data ◽  
Sea Surface ◽  
The Arctic ◽  
The Impact

The influence of sea-surface temperature (SST) on the lower troposphere and lower stratosphere temperature in the tropical, middle, and polar latitudes is studied for 1980–2019 based on the MERRA2, ERA5, and Met Office reanalysis data, and numerical modeling with a chemistry-climate model (CCM) of the lower and middle atmosphere. The variability of SST is analyzed according to Met Office and ERA5 data, while the variability of atmospheric temperature is investigated according to MERRA2 and ERA5 data. Analysis of sea surface temperature trends based on reanalysis data revealed that a significant positive SST trend of about 0.1 degrees per decade is observed over the globe. In the middle latitudes of the Northern Hemisphere, the trend (about 0.2 degrees per decade) is 2 times higher than the global average, and 5 times higher than in the Southern Hemisphere (about 0.04 degrees per decade). At polar latitudes, opposite SST trends are observed in the Arctic (positive) and Antarctic (negative). The impact of the El Niño Southern Oscillation phenomenon on the temperature of the lower and middle atmosphere in the middle and polar latitudes of the Northern and Southern Hemispheres is discussed. To assess the relative influence of SST, CO2, and other greenhouse gases’ variability on the temperature of the lower troposphere and lower stratosphere, numerical calculations with a CCM were performed for several scenarios of accounting for the SST and carbon dioxide variability. The results of numerical experiments with a CCM demonstrated that the influence of SST prevails in the troposphere, while for the stratosphere, an increase in the CO2 content plays the most important role.

scholarly journals Joint UAV channel modeling and power control for 5G IoT networks

2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
Xiuhua Fu ◽  
Tian Ding ◽  
Rongqun Peng ◽  
Cong Liu ◽  
Mohamed Cheriet
Keyword(s):  
Energy Efficiency ◽  
Power Control ◽  
Channel Model ◽  
Path Loss ◽  
Channel Modeling ◽  
Signal Propagation ◽  
Spectrum Efficiency ◽  
Propagation Path ◽  
Control Factor ◽  
The Impact

AbstractThis paper studies the communication problem between UAVs and cellular base stations in a 5G IoT scenario where multiple UAVs work together. We are dedicated to the uplink channel modeling and the performance analysis of the uplink transmission. In the channel model, we consider the impact of 3D distance and multi-UAVs reflection on wireless signal propagation. The 3D distance is used to calculate the path loss, which can better reflect the actual path loss. The power control factor is used to adjust the UAV's uplink transmit power to compensate for different propagation path losses, so as to achieve precise power control. This paper proposes a binary exponential power control algorithm suitable for 5G networked UAV transmitters and presents the entire power control process including the open-loop phase and the closed-loop phase. The effects of power control factors on coverage probability, spectrum efficiency and energy efficiency under different 3D distances are simulated and analyzed. The results show that the optimal power control factor can be found from the point of view of energy efficiency.

scholarly journals Dynamical Processes Related to the Appearance of the Okhotsk High during Early Midsummer

2007 ◽  
Vol 20 (19) ◽  
pp. 4982-4994 ◽  
Author(s):  
Naoki Sato ◽  
Masaaki Takahashi
Keyword(s):  
Energy Conversion ◽  
Heat Budget ◽  
Lower Troposphere ◽  
Positive Pressure ◽  
Basic Field ◽  
Anomaly Field ◽  
Anomaly Pattern ◽  
Pressure Anomaly ◽  
Okhotsk High ◽  
Upper Level

Abstract The authors identified an upper-level pressure anomaly pattern corresponding to the interannual variability of the Okhotsk high in midsummer (late July and early August) as a predominant anomaly pattern in the Northern Hemisphere, by using objectively analyzed data. According to the results of empirical orthogonal function (EOF) analyses and composite analyses, a positive pressure anomaly appeared near the tropopause over eastern Siberia in years with strong Okhotsk highs. Examination of the heat budget in the lower troposphere revealed that a negative surface temperature anomaly observed in northern Japan was brought by the advection of the climatological temperature gradient from the anomalous wind associated with the upper-level anticyclonic anomaly. It was also demonstrated that the anomaly field over Siberia does not accompany predominant vorticity forcing or Rossby wave propagation from the west with a specific phase. However, positive kinetic energy conversion from the climatological basic field to the anomaly field is estimated. The energy conversion contributes to maintaining the anomaly pattern. By the numerical experiments using a linear barotropic model, it is suggested that the upper-level anomaly pattern related to the anomalous Okhotsk high appears through the interaction with the climatological basic field, even though the external forcings are homogeneously distributed.

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