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 Model and Observational Analysis of the Northeast U.S. Regional Climate and Its Relationship to the PNA and NAO Patterns during Early Winter

2006 ◽  
Vol 134 (11) ◽  
pp. 3479-3505 ◽  
Author(s):  
M. Notaro ◽  
W-C. Wang ◽  
W. Gong
Keyword(s):  
New York ◽  
Great Lakes ◽  
Large Scale ◽  
Climate Model ◽  
Regional Climate ◽  
Early Winter ◽  
Upper Level ◽  
Upper Level Jet ◽  
The Impact ◽  
Nao Pattern

Abstract The relationship between the large-scale circulation and regional climate of the northeast United States is investigated for early winter using observational data and the State University of New York at Albany regional climate model. Simulated patterns of temperature, precipitation, and atmospheric circulation compare well with observations, despite a cold, dry bias. Ten December runs are analyzed to investigate the impact of the Pacific–North American (PNA) pattern on temperature, precipitation, clouds, and circulation features. During a positive PNA pattern, the simulated and observed eastern U.S. jet shifts to the southeast, coinciding with cold, dry conditions in the Northeast. This shift and intensification of the upper-level jet stream during a positive PNA pattern coincides with a greater frequency of cyclones and anticyclones along a distinct southwest–northeast track. Despite increased cyclone activity, total wintertime precipitation is below normal during a positive PNA pattern because of enhanced stability and subsidence over land, along with lower-atmospheric moisture content. Lower surface air temperatures during a positive PNA pattern result in enhanced simulated cloud cover over the Great Lakes and Atlantic Ocean due to increased thermal contrast and fluxes of sensible and latent heat, and a reduction in clouds over land. Interactions between the PNA and North Atlantic Oscillation (NAO) patterns impact the Northeast winter climate. Observed frontal passages through New York are most abundant during a negative PNA and positive NAO pattern, with a zonal upper-level jet positioned over New York. A positive PNA pattern is frequently characterized by an earlier observed Great Lakes ice season, while the greatest lake-effect snowfall occurs during a positive PNA and negative NAO pattern. The NAO pattern has the largest impact on northeast U.S. temperatures and the eastern U.S. upper-level jet during a positive PNA pattern.

scholarly journals Characteristics of Explosive Cyclones over the Northern Pacific

2017 ◽  
Vol 56 (12) ◽  
pp. 3187-3210 ◽  
Author(s):  
Shuqin Zhang ◽  
Gang Fu ◽  
Chungu Lu ◽  
Jingwu Liu
Keyword(s):  
Cold Season ◽  
Early Spring ◽  
Occurrence Frequency ◽  
Northwestern Pacific ◽  
Jet Stream ◽  
Central Pacific ◽  
Positive Vorticity ◽  
Northern Pacific ◽  
Upper Level ◽  
Upper Level Jet

AbstractExplosive cyclones (ECs) over the northern Pacific Ocean during the cold season (October–April) over a 15-yr (2000–15) period are analyzed by using the Final (FNL) Analysis data provided by the National Centers for Environmental Prediction. These ECs are stratified into four categories according to their intensity: weak, moderate, strong, and super ECs. In addition, according to the spatial distribution of their maximum-deepening-rate positions, ECs are further classified into five regions: the Japan–Okhotsk Sea (JOS), the northwestern Pacific (NWP), the west-central Pacific (WCP), the east-central Pacific (ECP), and the northeastern Pacific (NEP). The occurrence frequency of ECs shows evident seasonal variations for the various regions over the northern Pacific. NWP ECs frequently occur in winter and early spring, WCP and ECP ECs frequently occur in winter, and JOS and NEP ECs mainly occur in autumn and early spring. The occurrence frequency, averaged maximum deepening rate, and developing and explosive-developing lifetimes of ECs decrease eastward over the northern Pacific, excluding JOS ECs, consistent with the climatological intensity distributions of the upper-level jet stream, midlevel positive vorticity, and low-level baroclinicity. On the seasonal scale, the occurrence frequency and spatial distribution of ECs are highly correlated with the intensity and position of the upper-level jet stream, respectively, and also with those of midlevel positive vorticity and low-level baroclinicity. Over the northwestern Pacific, the warm ocean surface also contributes to the rapid development of ECs. The composite analysis indicates that the large-scale atmospheric environment for NWP and NEP ECs shows significant differences from that for the 15-yr cold-season average. The southwesterly anomalies of the upper-level jet stream and positive anomalies of midlevel vorticity favor the prevalence of NWP and NEP ECs.

scholarly journals Potential Vorticity Diagnosis in the Quasigeostrophic and Nonlinear Balance Systems

2008 ◽  
Vol 65 (1) ◽  
pp. 172-188 ◽  
Author(s):  
John W. Nielsen-Gammon ◽  
David A. Gold
Keyword(s):  
Potential Vorticity ◽  
Potential Temperature ◽  
Dominant Factor ◽  
Rossby Number ◽  
Level System ◽  
Balance Equations ◽  
Quantitative Diagnosis ◽  
Quantitative Accuracy ◽  
Atmospheric State ◽  
Upper Level

Abstract Quantitative diagnosis of low-Rossby-number flows using potential vorticity (PV) includes using elements of PV advection to deduce instantaneous tendencies of the balanced atmospheric state, most commonly the geopotential field. This technique, piecewise tendency diagnosis (PTD), is here applied with the prognostic balance equations (Bal-PTD) to obtain a quantitative dynamical diagnosis that in principle may be much more accurate than similar diagnoses using the quasigeostrophic (QG) equations. When both are applied systematically to a case of rapid oceanic cyclogenesis, differences are found to arise owing to a variety of factors. The dominant factor is differences in the vertical influence of PV anomalies, which affects the partitioning between local and remote processes. QG overestimates the effect of lower-level PV, including surface potential temperature, in amplifying and controlling the motion of the upper-level system. Other differences are found, but overall the QG diagnosis gives results that are qualitatively similar to the nonlinear balance diagnosis. Quantitative accuracy requires the use of Bal-PTD.

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.

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 TROCA ESTRATOSFERA-TROPOSFERA COMO UMA FONTE DE OZÔNIO PARA A CAMADA LIMITE PLANETÁRIA

2016 ◽  
Vol 38 ◽  
pp. 257
Author(s):  
Letícia De Oliveira dos Santos ◽  
Lucas Vaz Peres ◽  
Franciano Scremin Puhales ◽  
Vagner Anabor ◽  
Damaris Kirsch Pinheiro
Keyword(s):  
Stratospheric Ozone ◽  
Lower Troposphere ◽  
Lower Latitude ◽  
Jet Stream ◽  
Southern Brazil ◽  
Rio Grande Do Sul ◽  
Upper Level ◽  
Upper Level Jet ◽  
Jet Streak ◽  
Total Column

Stratosphere-troposphere exchange (STE) events were identified over southern Brazil acting as a stratospheric ozone source to the Planetary Boundary Layer (PBL) during 2011-2013 period. There were 13 events with direct influence between 29° and 31° S (center of Rio Grande do Sul), with increase in ozone total column. In these cases, 4 occurred in 2011, 5 in 2012 and 4 in 2013. They were divided: in relation to the exchange latitude, the upper-level Jet Stream act, altitude of source and arrive of air parcels. The air parcels cross the tropopause between 120 and 320 hPa (dynamic tropopause), entering troposphere until the lower troposphere. Most cases (30,8%) reached 1000 hPa and the rest between 600 and 900 hPa. Just in one day the STE occurred in a lower latitude than 29° S; in all the other days (92,3%), STEs occurred in higher latitudes than 31° S (the closer it gets to the pole, the bigger is the ozone concentration, except in Ozone Hole Influence events) or between 29° and 31° S. In most cases (61,5%) it was observed STE along with the Jet Streak act.

scholarly journals Increased turbulence in the Eurasian upper‐level jet stream in winter: past and future

2020 ◽  
Author(s):  
Yanmin Lv ◽  
Jianping Guo ◽  
Jian Li ◽  
Yi Han ◽  
Hui Xu ◽  
...  
Keyword(s):  
Jet Stream ◽  
Upper Level ◽  
Upper Level Jet
Sign in / Sign up

Export Citation Format

Share Document