scholarly journals Future changes in North Atlantic winter cyclones in CESM-LENS. Part I: cyclone intensity, PV anomalies and horizontal wind speed

2021 ◽  
Author(s):  
Edgar Dolores-Tesillos ◽  
Franziska Teubler ◽  
Stephan Pfahl
Keyword(s):  
Wind Speed ◽  
North Atlantic ◽  
Potential Vorticity ◽  
Structural Changes ◽  
Diabatic Heating ◽  
Horizontal Wind ◽  
Near Surface ◽  
Cyclone Intensity ◽  
Low Level ◽  
Upper Level

Abstract. Strong low-level winds associated with extratropical cyclones can cause substantial impacts on society. The wind intensity and the spatial distribution of wind maxima may change in a warming climate; however, the involved changes in cyclone structure and dynamics are unclear. Here, such structural changes of strong North Atlantic cyclones in a warmer climate close to the end of the current century are investigated with storm-relative composites based on Community Earth System Model Large Ensemble (CESM-LENS) simulations. Furthermore, a piecewise potential vorticity inversion is applied to associate such changes in low-level winds to changes in potential vorticity (PV) anomalies at different levels. Projected changes in cyclone intensity are generally rather small. However, using cyclone-relative composites, we identify an extended wind footprint southeast of the center of strong cyclones, where the wind speed tends to intensify in a warmer climate. Both an amplified low-level PV anomaly driven by enhanced diabatic heating and a dipole change in upper-level PV anomalies contribute to this wind intensification. On the contrary, wind changes associated with lower- and upper-level PV anomalies mostly compensate each other upstream of the cyclone center. Wind changes at upper levels are dominated by changes in upper-level PV anomalies and the background flow. All together, our results indicate that a complex interaction of enhanced diabatic heating and altered non-linear upper-tropospheric wave dynamics shape future changes in near-surface winds in North Atlantic cyclones.

Future changes in North Atlantic winter cyclones in CESM-LENS: cyclone intensity and horizontal wind speed

2021 ◽  
Author(s):  
Edgar Dolores Tesillos ◽  
Stephan Pfahl ◽  
Franziska Teubler
Keyword(s):  
Wind Speed ◽  
North Atlantic ◽  
Diabatic Heating ◽  
Horizontal Wind ◽  
Horizontal Wind Speed ◽  
Near Surface ◽  
Low Level ◽  
Current Century ◽  
Community Earth System Model ◽  
Upper Level

<p>Strong low-level winds are among the most impactful effects of extratropical cyclones on society.  The wind intensity and the spatial distribution of wind maxima may change in a warming climate, however, the dynamics involved are not clear. Here, structural and dynamical changes of North Atlantic cyclones in a warmer climate close to the end of the current century are investigated with storm-relative composites based on Community Earth System Model Large Ensemble (CESM-LE) simulations. Furthermore, a piecewise potential vorticity inversion is applied, to attribute such changes in low-level winds to changes in PV anomalies at different levels.</p><p>We identify an extended wind footprint southeast of the cyclone centre, where the wind speed tends to intensify in a warmer climate. Both an amplified low-level PV anomaly driven by enhanced diabatic heating and a dipole change in upper-level PV anomalies contribute to this wind intensification. On the contrary, wind changes associated with lower- and upper-level PV anomalies mostly compensate each other upstream of the cyclone center. Wind changes at upper levels are dominated by changes in upper-level PV anomalies and the background flow. All together, our results indicate that a complex interation of enhanced diabatic heating and altered upper-tropospheric wave dynamics shape future changes in near-surface winds in North Atlantic cyclones.</p>

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.

Intensification of Hurricane Sandy (2012) through Extratropical Warm Core Seclusion

2013 ◽  
Vol 141 (12) ◽  
pp. 4296-4321 ◽  
Author(s):  
Thomas J. Galarneau ◽  
Christopher A. Davis ◽  
Melvyn A. Shapiro
Keyword(s):  
New Jersey ◽  
Rhode Island ◽  
North Atlantic ◽  
Gulf Stream ◽  
Diabatic Heating ◽  
Hurricane Sandy ◽  
Cyclonic Vorticity ◽  
Near Surface ◽  
Warm Core ◽  
Upper Level

Abstract Hurricane Sandy's landfall along the New Jersey shoreline at 2330 UTC 29 October 2012 produced a catastrophic storm surge stretching from New Jersey to Rhode Island that contributed to damage in excess of $50 billion—the sixth costliest U.S. tropical cyclone on record since 1900—and directly caused 72 fatalities. Hurricane Sandy's life cycle was marked by two upper-level trough interactions while it moved northward over the western North Atlantic on 26–29 October. During the second trough interaction on 29 October, Sandy turned northwestward and intensified as cold continental air encircled the warm core vortex and Sandy acquired characteristics of a warm seclusion. The aim of this study is to determine the dynamical processes that contributed to Sandy's secondary peak in intensity during its warm seclusion phase using high-resolution numerical simulations. The modeling results show that intensification occurred in response to shallow low-level convergence below 850 hPa that was consistent with the Sawyer–Eliassen solution for the secondary circulation that accompanied the increased baroclinicity in the radial direction. Additionally, cyclonic vertical vorticity generated by tilting of horizontal vorticity along an axis of frontogenesis northwest of Sandy was axisymmetrized. The axis of frontogenesis was anchored to the Gulf Stream in a region of near-surface differential diabatic heating. The unusual northwestward track of Sandy allowed the cyclonic vorticity over the Gulf Stream to form ahead of the main vortex and be readily axisymmetrized. The underlying dynamics driving intensification were nontropical in origin, and supported the reclassification of Sandy as extratropical prior to landfall.

scholarly journals Direct radiative effect of the Russian wildfires and its impact on air temperature and atmospheric dynamics during August 2010

2014 ◽  
Vol 14 (4) ◽  
pp. 1999-2013 ◽  
Author(s):  
J. C. Péré ◽  
B. Bessagnet ◽  
M. Mallet ◽  
F. Waquet ◽  
I. Chiapello ◽  
...  
Keyword(s):  
Optical Properties ◽  
Wind Speed ◽  
Eastern Europe ◽  
Air Temperature ◽  
Air Entrainment ◽  
Atmospheric Dynamics ◽  
Horizontal Wind ◽  
Satellite Measurements ◽  
Near Surface ◽  
Aerosol Plume

Abstract. In this study, we investigate the shortwave aerosol direct radiative forcing (ADRF) and its feedback on air temperature and atmospheric dynamics during a major fire event that occurred in Russia during August 2010. The methodology is based on an offline coupling between the CHIMERE chemistry-transport and the Weather Research and Forecasting (WRF) models. First, simulations for the period 5–12 August 2010 have been evaluated by using AERONET (AErosol RObotic NETwork) and satellite measurements of the POLarization and Directionality of the Earth's Reflectance (POLDER) and the Cloud-Aerosol LIdar with Orthogonal Polarization (CALIOP) sensors. During this period, elevated POLDER aerosol optical thickness (AOT) is found over a large part of eastern Europe, with values above 2 (at 550 nm) in the aerosol plume. According to CALIOP observations, particles remain confined to the first five kilometres of the atmospheric layer. Comparisons with satellite measurements show the ability of CHIMERE to reproduce the regional and vertical distribution of aerosols during their transport from the source region. Over Moscow, AERONET measurements indicate an important increase of AOT (340 nm) from 0.7 on 5 August to 2–4 between 6 and 10 August when the aerosol plume was advected over the city. Particles are mainly observed in the fine size mode (radius in the range 0.2–0.4 μm) and are characterized by elevated single-scattering albedo (SSA) (0.95–0.96 between 440 and 1020 nm). Comparisons of simulations with AERONET measurements show that aerosol physical–optical properties (size distribution, AOT, SSA) have been well simulated over Moscow in terms of intensity and/or spectral dependence. Secondly, modelled aerosol optical properties have been used as input in the radiative transfer code of WRF to evaluate their direct radiative impact. Simulations indicate a significant reduction of solar radiation at the ground (up to 80–150 W m−2 in diurnal averages over a large part of eastern Europe due to the presence of the aerosol plume. This ADRF causes an important reduction of the near-surface air temperature between 0.2 and 2.6° on a regional scale. Moscow has been affected by the aerosol plume, especially between 6 and 10 August. During this period, aerosol causes a significant reduction of surface shortwave radiation (up to 70–84 W m−2 in diurnal averages) with a moderate part (20–30%) due to solar absorption within the aerosol layer. The resulting feedbacks lead to a cooling of the air up to 1.6° at the surface and 0.1° at an altitude of 1500–2000 m (in diurnal averages), that contribute to stabilize the atmospheric boundary layer (ABL). Indeed, a reduction of the ABL height of 13 to 65% has been simulated during daytime in presence of aerosols. This decrease is the result of a lower air entrainment as the vertical wind speed in the ABL is shown to be reduced by 5 to 80% (at midday) when the feedback of the ADRF is taken into account. However, the ADRF is shown to have a lower impact on the horizontal wind speed, suggesting that the dilution of particles would be mainly affected by the weakening of the ABL development and associated vertical entrainment. Indeed, CHIMERE simulations driven by the WRF meteorological fields including this ADRF feedback result in a large increase in the modelled near-surface PM10 concentrations (up to 99%). This is due to their lower vertical dilution in the ABL, which tend to reduce model biases with the ground PM10 values observed over Moscow during this specific period.

scholarly journals The Poleward Motion of Extratropical Cyclones from a Potential Vorticity Tendency Analysis

2016 ◽  
Vol 73 (4) ◽  
pp. 1687-1707 ◽  
Author(s):  
Talia Tamarin ◽  
Yohai Kaspi
Keyword(s):  
Heat Release ◽  
Latent Heat ◽  
Potential Vorticity ◽  
Growth Stage ◽  
Baroclinic Instability ◽  
Propagation Time ◽  
Latent Heat Release ◽  
Low Level ◽  
Upper Level ◽  
Tendency Analysis

Abstract The poleward propagation of midlatitude storms is studied using a potential vorticity (PV) tendency analysis of cyclone-tracking composites, in an idealized zonally symmetric moist GCM. A detailed PV budget reveals the important role of the upper-level PV and diabatic heating associated with latent heat release. During the growth stage, the classic picture of baroclinic instability emerges, with an upper-level PV to the west of a low-level PV associated with the cyclone. This configuration not only promotes intensification, but also a poleward tendency that results from the nonlinear advection of the low-level anomaly by the upper-level PV. The separate contributions of the upper- and lower-level PV as well as the surface temperature anomaly are analyzed using a piecewise PV inversion, which shows the importance of the upper-level PV anomaly in advecting the cyclone poleward. The PV analysis also emphasizes the crucial role played by latent heat release in the poleward motion of the cyclone. The latent heat release tends to maximize on the northeastern side of cyclones, where the warm and moist air ascends. A positive PV tendency results at lower levels, propagating the anomaly eastward and poleward. It is also shown here that stronger cyclones have stronger latent heat release and poleward advection, hence, larger poleward propagation. Time development of the cyclone composites shows that the poleward propagation increases during the growth stage of the cyclone, as both processes intensify. However, during the decay stage, the vertical alignment of the upper and lower PV anomalies implies that these processes no longer contribute to a poleward tendency.

scholarly journals Air/sea DMS gas transfer in the North Atlantic: evidence for limited interfacial gas exchange at high wind speed

2013 ◽  
Vol 13 (5) ◽  
pp. 13285-13322 ◽  
Author(s):  
T. G. Bell ◽  
W. De Bruyn ◽  
S. D. Miller ◽  
B. Ward ◽  
K. Christensen ◽  
...  
Keyword(s):  
Wind Speed ◽  
North Atlantic ◽  
Interfacial Stress ◽  
Horizontal Wind ◽  
Gas Transfer ◽  
High Wind ◽  
High Wind Speed ◽  
Wind Speeds ◽  
The North ◽  
The North Atlantic

Abstract. Shipboard measurements of eddy covariance DMS air/sea fluxes and seawater concentration were carried out in the North Atlantic bloom region in June/July 2011. Gas transfer coefficients (k660) show a linear dependence on mean horizontal wind speed at wind speeds up to 11 m s−1. At higher wind speeds the relationship between k660 and wind speed weakens. At high winds, measured DMS fluxes were lower than predicted based on the linear relationship between wind speed and interfacial stress extrapolated from low to intermediate wind speeds. In contrast, the transfer coefficient for sensible heat did not exhibit this effect. The apparent suppression of air/sea gas flux at higher wind speeds appears to be related to sea state, as determined from shipboard wave measurements. These observations are consistent with the idea that long waves suppress near surface water side turbulence, and decrease interfacial gas transfer. This effect may be more easily observed for DMS than for less soluble gases, such as CO2, because the air/sea exchange of DMS is controlled by interfacial rather than bubble-mediated gas transfer under high wind speed conditions.

scholarly journals Low-Level Atmospheric Responses to the Sea Surface Temperature Fronts in the Chukchi and Bering Seas

2021 ◽  
Vol 8 ◽  
Author(s):  
Yoshimi Kawai
Keyword(s):  
Sea Ice ◽  
Surface Temperature ◽  
Bering Sea ◽  
Diabatic Heating ◽  
Chukchi Sea ◽  
Western Boundary ◽  
Turbulent Heat ◽  
Near Surface ◽  
Low Level ◽  
The Bering Sea

Atmospheric responses to ocean surface temperature (ST) fronts related to western boundary currents have been extensively analyzed over the last two decades. However, the organized near-surface response to ST, which is defined as the temperature of open water and sea ice, excluding land surface, at higher latitudes where sea ice exists has been rarely investigated due to the difficulties of observations. Here, 32 years of high-resolution atmospheric reanalysis data are analyzed to determine the atmospheric responses to ST fronts in the Bering Sea and Chukchi Sea. In the Chukchi Sea, the convergence of 10-m-high wind increases in October and November, when the horizontal gradient and Laplacian of ST become noticeable. On the other hand, an ST contrast between the continental shelf and the southwestern deep basin develops in winter in the Bering Sea. In both seas, the spatial distribution of surface wind convergence and the Laplacians of ST and sea level pressure agree well with each other, demonstrating the pressure adjustment mechanism. The vertical mixing mechanism is also confirmed in both seas. Ascending motion and diabatic heating develop over the Chukchi Sea in late autumn, but are confined to the lower troposphere. Turbulent heat fluxes at the surface become especially large in this season, resulting in an increase of diabatic heating and low-level clouds. Low-level clouds and downward shortwave radiation exhibit contrasting behavior across the shelf break in the Bering Sea that corresponds to the ST distribution, which is regulated by the bottom topography.

Double warm-core structure and potential vorticity diagnosis during the rapid intensification of Supertyphoon Lekima (2019)

2021 ◽  
Author(s):  
Donglei Shi ◽  
Guanghua Chen
Keyword(s):  
Potential Vorticity ◽  
Diabatic Heating ◽  
Inner Core ◽  
Deep Layer ◽  
Rapid Intensification ◽  
Latent Heat Release ◽  
Wind Fields ◽  
Warm Core ◽  
Upper Level ◽  
Pv Generation

AbstractThe rapid intensification (RI) of supertyphoon Lekima (2019) is investigated from the perspective of balanced potential vorticity (PV) dynamics using a high-resolution numerical simulation. The PV budget shows that the inner-core PV anomalies (PVAs) formed during the RI mainly comprise an eyewall PV tower generated by diabatic heating, a high-PV bridge extending into the eye resulting from the PV mixing, and an upper-tropospheric high-PV core induced by the PV intrusion from stratosphere. The inversion of the total PVA at the end of the RI captures about 90% of changes in pressure and wind fields, indicating that the storm is quasi-balanced. The piecewise PV inversion further demonstrates that the eyewall and mixed PVAs induce the upper-level and midlevel warm cores in the eye region, respectively. The two warm cores cause nearly all the balanced central pressure decrease and thus dominate the RI, with the contribution of the upper warm core being twice that of the midlevel one. In contrast, the upper-tropospheric PV core induces significant warming near the tropopause and deep-layer cooling beneath, reinforcing the upper-level warm core but causing little surface pressure drop.By comparing the diabatic PV generation due to the convective burst (CB) and non-CB precipitation, we found that the non-CB precipitation accounts for a larger portion for the eyewall PVA and thus the associated upper-level warming, distinct from previous studies that primarily attributed the upper-level warm-core formation to the CB. Nevertheless, CBs act to be more efficient PV generators due to their vigorous latent heat release and are thus favorable for RI.

scholarly journals The Microphysical Building Blocks of Low-Level Potential Vorticity Anomalies in an Idealized Extratropical Cyclone

2017 ◽  
Vol 74 (5) ◽  
pp. 1403-1416 ◽  
Author(s):  
Bas Crezee ◽  
Hanna Joos ◽  
Heini Wernli
Keyword(s):  
Potential Vorticity ◽  
Channel Model ◽  
Building Blocks ◽  
Extratropical Cyclone ◽  
Positive Anomaly ◽  
Snow Melting ◽  
Near Surface ◽  
Low Level ◽  
Warm Front ◽  
Microphysical Processes

Abstract Diabatically generated low-level potential vorticity (PV) anomalies in extratropical cyclones enhance near-surface winds and influence the cyclone’s development. Positive and negative PV anomalies in the warm-frontal region of an extratropical cyclone, simulated with an idealized moist baroclinic channel model, are investigated to identify the microphysical processes that produce them. Using a novel method based on backward trajectories from the PV anomalies, the contribution of different microphysical processes to the formation of the anomalies is quantified. It is found that, for each anomaly, typically one specific microphysical process takes the leading role in its diabatic generation. A large but rather weak low- and midlevel positive anomaly is produced by depositional growth of ice and snow. Two smaller but stronger positive anomalies at lower levels are generated mainly by in-cloud condensational heating at the warm front and below-cloud rain evaporation and snow melting 200 km farther north. In addition, near-surface negative anomalies are produced by snow melting and snow sublimation. In summary, this idealized study reveals that (i) a variety of microphysical processes are involved in generating the complex mesoscale PV structures along the warm front; (ii) the model representation of these processes, some of them still insufficiently understood and parameterized, therefore matters for an accurate prediction of these features; (iii) below-cloud processes are also relevant for PV anomalies located in clouds, owing to accumulation of diabatic PV tendencies along ascending air parcels; and (iv) the diabatic history of the air parcels is essential in order to explain the observed PV pattern.

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