scholarly journals Thermal advection, vorticity advection and potential vorticity advection in extra-tropical, synoptic-scale development

2003 ◽  
Vol 10 (3) ◽  
pp. 281-292 ◽  
Author(s):  
E B Carroll
Keyword(s):  
Scale Development ◽  
Potential Vorticity ◽  
Synoptic Scale ◽  
Thermal Advection ◽  
Vorticity Advection

Interactions between Water Vapor and Potential Vorticity in Synoptic-Scale Monsoonal Disturbances: Moisture Vortex Instability

2018 ◽  
Vol 75 (6) ◽  
pp. 2083-2106 ◽  
Author(s):  
Ángel F. Adames ◽  
Yi Ming
Keyword(s):  
Potential Vorticity ◽  
Baroclinic Instability ◽  
Relative Role ◽  
Synoptic Scale ◽  
Vortex Instability ◽  
Tropical Variability ◽  
Moisture Advection ◽  
Energy Gradient ◽  
Gross Moist Stability ◽  
Static Energy

AbstractSouth Asian monsoon low pressure systems, referred to as synoptic-scale monsoonal disturbances (SMDs), are convectively coupled cyclonic disturbances that are responsible for up to half of the total monsoon rainfall. In spite of their importance, the mechanisms that lead to the growth of these systems have remained elusive. It has long been thought that SMDs grow because of a variant of baroclinic instability that includes the effects of convection. Recent work, however, has shown that this framework is inconsistent with the observed structure and dynamics of SMDs. Here, we present an alternative framework that may explain the growth of SMDs and may also be applicable to other modes of tropical variability. Moisture is prognostic and is coupled to precipitation through a simplified Betts–Miller scheme. Interactions between moisture and potential vorticity (PV) in the presence of a moist static energy gradient can be understood in terms of a “gross” PV (qG) equation. The qG summarizes the dynamics of SMDs and reveals the relative role that moist and dry dynamics play in these disturbances, which is largely determined by the gross moist stability. Linear solutions to the coupled PV and moisture equations reveal Rossby-like modes that grow because of a moisture vortex instability. Meridional temperature and moisture advection to the west of the PV maximum moisten and destabilize the column, which results in enhanced convection and SMD intensification through vortex stretching. This instability occurs only if the moistening is in the direction of propagation of the SMD and is strongest at the synoptic scale.

Evolution of African Easterly Waves in Potential Vorticity Fields

2012 ◽  
Vol 140 (11) ◽  
pp. 3634-3652 ◽  
Author(s):  
Bryce Tyner ◽  
Anantha Aiyyer
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
Potential Vorticity ◽  
African Easterly Waves ◽  
Synoptic Scale ◽  
Easterly Waves ◽  
Tropical Cyclone Formation ◽  
Closed Circulation ◽  
Isentropic Potential Vorticity

Abstract The evolution of African easterly waves (AEWs) leading to tropical cyclones (TCs) in the Atlantic during 2000–08 is examined from isentropic potential vorticity (PV) and Lagrangian streamline perspectives. Tropical cyclone formation is commonly preceded by axisymmetrization of PV, scale contraction of the wave, and formation of a closed circulation within the wave. In these cases, PV associated with the synoptic-scale wave is irreversibly deformed and subsumed within the developing vortex. Less commonly, filamentation of the PV leads to separation and independent propagation of the wave and the TC vortex. In an example presented here, the remnant wave with a closed circulation persisted for several days after separation from the TC. A second TC did not result, consistent with several past studies that show that a midtropospheric closed gyre is not sufficient for TC genesis. Sometimes, an AEW and a weak TC remain coupled for a few days, followed by the dissipation of the TC and the continued propagation of the wave. Merger of tropical and extratropical PV anomalies is also often observed and likely helps maintain some waves. The results of this study are broadly consistent with recent Lagrangian analyses of AEW evolution during TC genesis.

scholarly journals Moist Static Potential Vorticity Budget in Tropical Motion Systems

2021 ◽  
Keyword(s):  
Potential Vorticity ◽  
Linear Regression Analysis ◽  
Potential Temperature ◽  
Wave Activity ◽  
The Other ◽  
Eastern Pacific ◽  
Synoptic Scale ◽  
Static Potential ◽  
Horizontal Advection ◽  
Other Hand

Abstract Analyses of simple models of moist tropical motion systems reveal that the column-mean moist static potential vorticity (MSPV) can explain their propagation and growth. The MSPV is akin to the equivalent PV except it uses moist static energy (MSE) instead of the equivalent potential temperature. Examination of an MSPV budget that is scaled for moist off-equatorial synoptic-scale systems reveals that α, the ratio between the vertical gradients of latent and dry static energies, describes the relative contribution of dry and moist advective processes to the evolution of MSPV. Horizontal advection of the moist component of MSPV, a process akin to horizontal MSE advection, governs the evolution of synoptic-scale systems in regions of high humidity. On the other hand, horizontal advection of dry PV predominates in a dry atmosphere. Derivation of a “moist static” wave activity density budget reveals that α also describes the relative importance of moist and dry processes to wave activity amplification and decay. Linear regression analysis of the MSPV budget in eastern Pacific easterly waves shows that the MSPV anomalies originate over the eastern Caribbean and propagate westward due to dry PV advection. They are amplified by the fluxes of the moist component of MSPV over the Caribbean sea and over the eastern Pacific from 105-130°W, underscoring the importance of moist processes in these waves. On the other hand, dry PV convergence amplifies the waves from 90-100°W, likely as a result of the barotropic energy conversions that occur in this region.

scholarly journals Development of North Atlantic Tropical Disturbances near Upper-Level Potential Vorticity Streamers

2015 ◽  
Vol 72 (2) ◽  
pp. 572-597 ◽  
Author(s):  
Thomas J. Galarneau ◽  
Ron McTaggart-Cowan ◽  
Lance F. Bosart ◽  
Christopher A. Davis
Keyword(s):  
Water Vapor ◽  
North Atlantic ◽  
Potential Vorticity ◽  
Synoptic Climatology ◽  
Primary Role ◽  
Synoptic Scale ◽  
Near Surface ◽  
The North ◽  
The North Atlantic ◽  
Upper Level

Abstract Tropical cyclone (TC) development near upper-level potential vorticity (PV) streamers in the North Atlantic is studied from synoptic climatology, composite, and case study perspectives. Midlatitude anticyclonic wave breaking is instrumental in driving PV streamers into subtropical and tropical latitudes, in particular near the time-mean midocean trough identified previously as the tropical upper-tropospheric trough. Twelve TCs developed within one Rossby radius of PV streamers in the North Atlantic from June through November 2004–08. This study uses composite analysis in the disturbance-relative framework to compare the structural and thermodynamic evolution for developing and nondeveloping cases. The results show that incipient tropical disturbances are embedded in an environment characterized by 850–200-hPa westerly vertical wind shear and mid- and upper-level quasigeostrophic ascent associated with the PV streamer, with minor differences between developing and nondeveloping cases. The key difference in synoptic-scale flow between developing and nondeveloping cases is the strength of the anticyclone north of the incipient tropical disturbance. The developing cases are marked by a stronger near-surface pressure gradient and attendant easterly flow north of the vortex, which drives enhanced surface latent heat fluxes and westward (upshear) water vapor transport. This evolution in water vapor facilitates an upshear propagation of convection, and the diabatically influenced divergent outflow erodes the PV streamer aloft by negative advection of PV by the divergent wind. This result suggests that the PV streamer plays a secondary role in TC development, with the structure and intensity of the synoptic-scale anticyclone north of the incipient vortex playing a primary role.

scholarly journals Coherent Potential Vorticity Maxima and Their Relationship to Extreme Summer Rainfall in the Australian and North African Tropics

2016 ◽  
Vol 66 (4) ◽  
pp. 424
Author(s):  
Lam P. Hoang ◽  
Michael J. Reeder ◽  
Gareth. J. Berry ◽  
Juliane Schwendike
Keyword(s):  
Potential Vorticity ◽  
West African Monsoon ◽  
Lower Troposphere ◽  
Extreme Rainfall ◽  
Summer Rainfall ◽  
Horizontal Wind ◽  
Synoptic Scale ◽  
North African ◽  
Eastern Australia ◽  
The Tropics

Extreme rainfall in the tropics is frequently linked with coherent synoptic-scale potential vorticity (PV) disturbances. Here, an objective technique is used to identify coherent synoptic-scale cyclonic PV maxima with a focus on those that occur during summer over the African and Australian tropics. These two regions are chosen for comparison because of their geographical and climatological similarities. In particular, in both regions oceans lie equatorward and extensive deserts lie pole-ward, a juxtaposition that produces a reversal in the mean north-south temperature gradient and, through thermal wind, a low level easterly jet.In general, in the lower troposphere there are more coherent PV maxima in the tropics in the summer hemisphere than the winter hemisphere. These coherent PV maxima generally move with the background flow in the lower troposphere. The largest meridional flux of coherent PV maxima lies along eastern Australia with about half of the coherent PV maxima generated through the filamentaton and eventual isolation of midlatitude PV. In contrast, in the north African tropics, coherent PV maxima are generated mostly in the tropics and move westward through the west African monsoon region.Composites based on the extreme rainfall days for two regions are broadly similar with large, statistically significant PV maxima to the east of the maximum positive rainfall anomalies. The vertical structures of the PV fields in the two regions reveal a cyclonic PV maximum in the mid-troposphere collocated with the maximum of diabatic heating. The composite horizontal wind structures in the Australian tropics show structures similar to mesoscale convective systems (MCSs), whereas in the African tropics, they are similar to easterly waves.

scholarly journals A Wavelet Representation of Synoptic-Scale Coherent Structures

2008 ◽  
Vol 65 (10) ◽  
pp. 3116-3138 ◽  
Author(s):  
Matthieu Plu ◽  
Philippe Arbogast ◽  
Alain Joly
Keyword(s):  
Potential Vorticity ◽  
Coherent Structures ◽  
Physical Reality ◽  
Invariance Property ◽  
Translation Invariance ◽  
Recent Theory ◽  
Two Dimensional ◽  
Synoptic Scale ◽  
Wavelet Representation ◽  
Potential Vorticity Inversion

Midlatitude cyclogenesis as interpreted in the framework of either baroclinic development or potential vorticity thinking heavily relies on the concept of synoptic-scale anomaly. Given the existence of potential vorticity inversion and attribution, what is at stake to provide a mathematical definition for this concept is a complete finite-amplitude alternative to the linear-based theory of cyclogenesis. The existence of a reasonably objective way to represent anomalies in both real and idealized flows would not only help understanding cyclogenesis, it would also have many other applications for both theory and in practical forecasts. Inspired by the recent theory of wavelet representation of coherent structures in two-dimensional fluid mechanics, a wavelet representation of three-dimensional potential vorticity anomalies is built. This algorithm relies on the selection of the appropriate two-dimensional wavelet coefficients from the stationary wavelet transform in order to guarantee the critical translation-invariance property. The sensitivity of the algorithm to the position, size, and shape of the structures is assessed. The wavelet extraction is then applied to the upper-level precursor of a real-case storm of December 1999 and is compared to a basic monopolar extraction. Using potential vorticity inversion and forecasts with a primitive-equation model, it is found that both anomalies have similar implications on the development of the surface cyclone. However, the coherence in time of the extracted wavelet structure in the forecast and analysis sequence is more satisfactory than the extracted monopole: this suggests that the underlying mathematical description of an anomaly proposed here does, indeed, point toward the direction of an actual physical reality of the concept.

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