scholarly journals A Climatology of the Tropospheric Thermal Stratification Using Saturation Potential Vorticity

2007 ◽  
Vol 20 (24) ◽  
pp. 5977-5991 ◽  
Author(s):  
Robert L. Korty ◽  
Tapio Schneider
Keyword(s):  
Potential Vorticity ◽  
Thermal Stratification ◽  
Large Scale ◽  
Lower Troposphere ◽  
Reanalysis Data ◽  
Reanalysis Dataset ◽  
Air Masses ◽  
Slantwise Convection ◽  
The Tropics ◽  
Global Reanalysis

Abstract The condition of convective neutrality is assessed in the troposphere by calculating the saturation potential vorticity P* from reanalysis data. Regions of the atmosphere in which saturation entropy is constant along isosurfaces of absolute angular momentum, a state indicative of slantwise-convective neutrality, have values of P* equal to zero. In a global reanalysis dataset spanning the years 1970–2004, tropospheric regions are identified in which P* is near zero, implying that vertical convection or slantwise convection may be important in determining the local thermal stratification. Convectively neutral air masses are common not only in the Tropics but also in higher latitudes, for example, over midlatitude continents in summer and in storm tracks over oceans in winter. Large-scale eddies appear to stabilize parts of the lower troposphere, particularly in winter.

scholarly journals Analysis of a rapid increase of stratospheric ozone during late austral summer 2008 over Kerguelen (49.4° S, 70.3° E)

2011 ◽  
Vol 11 (1) ◽  
pp. 363-373 ◽  
Author(s):  
H. Bencherif ◽  
L. El Amraoui ◽  
G. Kirgis ◽  
J. Leclair De Bellevue ◽  
A. Hauchecorne ◽  
...  
Keyword(s):  
Potential Vorticity ◽  
Large Scale ◽  
Lower Stratosphere ◽  
Transport Model ◽  
Stratospheric Ozone ◽  
Three Dimensional ◽  
Austral Summer ◽  
Air Masses ◽  
Global Mapping ◽  
The Tropics

Abstract. This paper reports on an increase of ozone event observed over Kerguelen (49.4° S, 70.3° E) in relationship with large-scale isentropic transport. This is evidenced by ground-based observations (co-localised radiosonde and SAOZ experiments) together with satellite global observations (Aura/MLS) assimilated into MOCAGE, a Méteo-France model. The study is based on the analyses of the first ozonesonde experiment never recorded at the Kerguelen site within the framework of a French campaign called ROCK that took place from April to August 2008. Comparisons and interpretations of the observed event are supported by co-localised SAOZ observations, by global mapping of tracers (O3, N2O and columns of O3) from Aura/MLS and Aura/OMI experiments, and by model simulations of Ertel Potential Vorticity initialised by the ECMWF (European Centre for Medium-Range Weather Forecasts) data reanalyses. Satellite and ground-based observational data revealed a consistent increase of ozone in the local stratosphere by mid-April 2008. Additionally, Ozone (O3) and nitrous oxide (N2O) profiles obtained during January–May 2008 using the Microwave Limb Sounder (MLS) aboard the Aura satellite are assimilated into MOCAGE (MOdèle de Chimie Atmosphérique à Grande Echelle), a global three-dimensional chemistry transport model of Météo-France. The assimilated total O3 values are consistent with SAOZ ground observations (within ±5%), and isentropic distributions of O3 match well with maps of advected potential vorticity (APV) derived from the MIMOSA model, a high-resolution advection transport model, and from the ECMWF reanalysis. The event studied seems to be related to the isentropic transport of air masses that took place simultaneously in the lower- and middle-stratosphere, respectively from the polar region and from the tropics to the mid-latitudes. In fact, the ozone increase observed by mid April 2008 resulted simultaneously: (1) from an equator-ward departure of polar air masses characterised with a high-ozone layer in the lower stratosphere (near the 475 K isentropic level), and (2) from a reverse isentropic transport from the tropics to mid- and high-latitudes in the upper stratosphere (nearby the 700 K level). The increase of ozone observed over Kerguelen from the 16-April ozonesonde profile is thus attributed to a concomitant isentropic transport of ozone in two stratospheric layers: the tropical air moving southward and reaching over Kerguelen in the upper stratosphere, and the polar air passing over the same area but in the lower stratosphere.

Lower-Tropospheric Eddy Momentum Fluxes in Idealized Models and Reanalysis Data

2017 ◽  
Vol 74 (11) ◽  
pp. 3787-3797 ◽  
Author(s):  
Nicholas J. Lutsko ◽  
Isaac M. Held ◽  
Pablo Zurita-Gotor ◽  
Amanda K. O’Rourke
Keyword(s):  
Potential Vorticity ◽  
Lower Layer ◽  
Baroclinic Instability ◽  
Lower Troposphere ◽  
Reanalysis Data ◽  
Equation Model ◽  
Long Waves ◽  
Reanalysis Dataset ◽  
Upper Troposphere ◽  
Momentum Fluxes

Abstract In Earth’s atmosphere eddy momentum fluxes (EMFs) are largest in the upper troposphere, but EMFs in the lower troposphere, although modest in amplitude, have an intriguing structure. To document this structure, the EMFs in the lower tropospheres of a two-layer quasigeostrophic model, a primitive equation model, and the Southern Hemisphere of a reanalysis dataset are investigated. The lower-tropospheric EMFs are very similar in the cores of the jets in both models and the reanalysis data, with EMF divergence (opposing the upper-tropospheric convergence) due to relatively long waves with slow eastward phase speeds and EMF divergence (as in the upper troposphere) due to shorter waves with faster eastward phase speeds. As the two-layer model is able to capture the EMF divergence by long waves, a qualitative picture of the underlying dynamics is proposed that relies on the negative potential vorticity gradient in the lower layer of the model. Eddies excited by baroclinic instability mix efficiently through a wide region in the lower layer, centered on the latitude of maximum westerlies and encompassing the lower-layer critical latitudes. Near these critical latitudes, the mixing is enhanced, resulting in increased EMF convergence, with compensating EMF divergence in the center of the jet. The EMF convergence at faster phase speeds is due to deep eddies that propagate on the upper-tropospheric potential vorticity gradient.

scholarly journals Tropical Cyclogenesis in the Western North Pacific as Revealed by the 2008–09 YOTC Data*

2013 ◽  
Vol 28 (4) ◽  
pp. 1038-1056 ◽  
Author(s):  
Yamei Xu ◽  
Tim Li ◽  
Melinda Peng
Keyword(s):  
Rossby Wave ◽  
Wave Energy ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Lower Troposphere ◽  
Energy Dispersion ◽  
Reanalysis Dataset ◽  
Initial Development ◽  
Wave Trains

Abstract The Year of Tropical Convection (YOTC) high-resolution global reanalysis dataset was analyzed to reveal precursor synoptic-scale disturbances related to tropical cyclone (TC) genesis in the western North Pacific (WNP) during the 2008–09 typhoon seasons. A time filtering is applied to the data to isolate synoptic (3–10 day), quasi-biweekly (10–20 day), and intraseasonal (20–90 day) time-scale components. The results show that four types of precursor synoptic disturbances associated with TC genesis can be identified in the YOTC data. They are 1) Rossby wave trains associated with preexisting TC energy dispersion (TCED) (24%), 2) synoptic wave trains (SWTs) unrelated to TCED (32%), 3) easterly waves (EWs) (16%), and 4) a combination of either TCED-EW or SWT-EW (24%). The percentage of identifiable genesis events is higher than has been found in previous analyses. Most of the genesis events occurred when atmospheric quasi-biweekly and intraseasonal oscillations are in an active phase, suggesting a large-scale control of low-frequency oscillations on TC formation in the WNP. For genesis events associated with SWT and EW, maximum vorticity was confined in the lower troposphere. During the formation of Jangmi (2008), maximum Rossby wave energy dispersion appeared in the middle troposphere. This differs from other TCED cases in which energy dispersion is strongest at low level. As a result, the midlevel vortex from Rossby wave energy dispersion grew faster during the initial development stage of Jangmi.

Method for Identifying and Clustering Rossby Wave Breaking Events in the Northern Hemisphere

2021 ◽  
pp. 17-28
Author(s):  
A. V. Gochakov ◽  
◽  
O. Yu. Antokhina ◽  
V. N. Krupchatnikov ◽  
Yu. V. Martynova ◽  
...  
Keyword(s):  
Rossby Wave ◽  
Potential Vorticity ◽  
Wave Breaking ◽  
Large Scale ◽  
Method Development ◽  
Spatial Clustering ◽  
Potential Temperature ◽  
Reanalysis Data ◽  
Rossby Wave Breaking ◽  
Dynamic Phenomena

Many large-scale dynamic phenomena in the Earth’s atmosphere are associated with the processes of propagation and breaking of Rossby waves. A new method for identifying the Rossby wave breaking (RWB) is proposed. It is based on the detection of breakings centers by analyzing the shape of the contours of potential vorticity or temperature on quasimaterial surfaces: isentropic and iserthelic (surfaces of constant Ertel potential vorticity (PV)), with further RWB center clustering to larger regions. The method is applied to the set of constant PV levels (0.3 to 9.8 PVU with a step of 0.5 PVU) at the level of potential temperature of 350 K for 12:00 UTC. The ERA-Interim reanalysis data from 1979 to 2019 are used for the method development. The type of RWB (cyclonic/anticyclonic), its area and center are determined by analyzing the vortex geometry at each PV level for every day. The RWBs obtained at this stage are designated as elementary breakings. Density-Based Spatial Clustering of Applications with Noise algorithm (DBSCAN) was applied to all elementary breakings for each month. As a result, a graphic dataset describing locations and dynamics of RWBs for every month from 1979 to 2019 is formed. The RWB frequency is also evaluated for each longitude, taking into account the duration of each RWB and the number of levels involved, as well as the anomalies of these parameters.

Thermal Stratification in Simulations of Warm Climates: A Climatology Using Saturation Potential Vorticity

2016 ◽  
Vol 29 (14) ◽  
pp. 5083-5102 ◽  
Author(s):  
Ryan A. Zamora ◽  
Robert L. Korty ◽  
Matthew Huber
Keyword(s):  
Potential Vorticity ◽  
Temporal Distribution ◽  
Reanalysis Data ◽  
Storm Tracks ◽  
The Arctic ◽  
Moist Convection ◽  
Air Masses ◽  
Wide Range ◽  
Carbon Dioxide Levels ◽  
Lapse Rates

Abstract The spatial and temporal distribution of stable and convectively neutral air masses is examined in climate simulations with carbon dioxide levels spanning from modern-day values to very high levels that produce surface temperatures relevant to the hottest climate of the past 65 million years. To investigate how stability with respect to slantwise and upright moist convection changes across a wide range of climate states, the condition of moist convective neutrality in climate experiments is assessed using metrics based upon the saturation of potential vorticity, which is zero when temperature profiles are moist adiabatic profiles along vortex lines. The modern climate experiment reproduces previously reported properties from reanalysis data, in which convectively neutral air masses are common in the tropics and locally at higher latitudes, especially over midlatitude continents in summer and ocean storm tracks in winter. The frequency and coverage of air masses with higher stabilities declines in all seasons at higher latitudes with warming; the hottest case features convectively neutral air masses in the Arctic a majority of the time in January and nearly universally in July. The contribution from slantwise convective motions (as distinct from upright convection) is generally small outside of midlatitude storm tracks, and it declines in the warmer climate experiments, especially during summer. These findings support the conjecture that moist adiabatic lapse rates become more widespread in warmer climates, providing a physical basis for using this assumption in estimating paleoaltimetry during warm intervals such as the early Eocene.

scholarly journals A climatology of formation conditions for aerodynamic contrails

2013 ◽  
Vol 13 (21) ◽  
pp. 10847-10857 ◽  
Author(s):  
K. Gierens ◽  
F. Dilger
Keyword(s):  
Climate Impact ◽  
Reanalysis Data ◽  
Air Traffic ◽  
Liquid Droplets ◽  
Atmospheric Conditions ◽  
Climate Effect ◽  
Ice Clouds ◽  
Formation Conditions ◽  
The Tropics ◽  
Global Reanalysis

Abstract. Aircraft at cruise levels can cause two kinds of contrails, the well known exhaust contrails and the less well-known aerodynamic contrails. While the possible climate impact of exhaust contrails has been studied for many years, research on aerodynamic contrails began only a few years ago and nothing is known about a possible contribution of these ice clouds to climate impact. In order to make progress in this respect, we first need a climatology of their formation conditions and this is given in the present paper. Aerodynamic contrails are defined here as line shaped ice clouds caused by aerodynamically triggered cooling over the wings of an aircraft in cruise which become visible immediately at the trailing edge of the wing or close to it. Effects at low altitudes like condensation to liquid droplets and their potential heterogeneous freezing are excluded from our definition. We study atmospheric conditions that allow formation of aerodynamic contrails. These conditions are stated and then applied to atmospheric data: first to a special case where an aerodynamic contrail was actually observed and then to a full year of global reanalysis data. We show where, when (seasonal variation), and how frequently (probability) aerodynamic contrails can form, and how this relates to actual patterns of air traffic. We study the formation of persistent aerodynamic contrails as well. Furthermore, we check whether aerodynamic and exhaust contrails can coexist in the atmosphere. We show that visible aerodynamic contrails are possible only in an altitude range between roughly 540 and 250 hPa, and that the ambient temperature is the most important parameter, not the relative humidity. Finally, we argue that currently aerodynamic contrails have a much smaller climate effect than exhaust contrails, which may however change in future with more air traffic in the tropics.

scholarly journals Characterizing quasi-biweekly variability of the Asian monsoon anticyclone using potential vorticity and large-scale geopotential height field

2020 ◽  
Vol 20 (22) ◽  
pp. 13857-13876
Author(s):  
Arata Amemiya ◽  
Kaoru Sato
Keyword(s):  
Potential Vorticity ◽  
Geopotential Height ◽  
Large Scale ◽  
Asian Monsoon ◽  
Reanalysis Data ◽  
Longitudinal Distribution ◽  
Middle Latitudes ◽  
Subseasonal Variability ◽  
Westward Movement ◽  
Isentropic Surface

Abstract. The spatial pattern of subseasonal variability of the Asian monsoon anticyclone is analyzed using long-term reanalysis data, focusing on the large-scale longitudinal movement. The air inside the anticyclone is quantified by a thickness-weighted low-PV (potential vorticity) area on an isentropic surface. It is shown that the longitudinal movement of the air inside the Asian monsoon anticyclone has a timescale of 1 to 2 weeks, which is shorter than the monthly dominant timescale of the variability in the anticyclone intensity. The movement of the anticyclonic air is suggested to be largely controlled by passive advection. The typical time evolution of the variability pattern, explained by two leading empirical orthogonal function (EOF) components of 100 hPa geopotential height, shows large-scale geopotential anomalies moving westward spanning from low to middle latitudes. This corresponds well with the rapid westward movement of low-PV air known as “eddy shedding” and following the eastward retreat of the anticyclonic air. The two EOF components can also explain the bimodal longitudinal distribution of geopotential maximum location.

scholarly journals An Objective Identification and Climatology of Upper-Tropospheric Jets near Atlantic Tropical Cyclones

2020 ◽  
Vol 148 (7) ◽  
pp. 3015-3036
Author(s):  
Levi P. Cowan ◽  
Robert E. Hart
Keyword(s):  
Tropical Cyclones ◽  
Potential Vorticity ◽  
Clustering Analysis ◽  
Large Scale ◽  
Reanalysis Data ◽  
Atlantic Basin ◽  
Jet Behavior ◽  
Consistent Feature ◽  
Large Scale Flow ◽  
Westerly Jets

Abstract An objective algorithm is developed for identifying jets in 200-hPa flow and applied to reanalysis data within 2000 km of Atlantic tropical cyclones (TCs) during 1979–2015. The resulting set of 16 512 jets is analyzed both qualitatively and quantitatively to describe the climatology of TC–jet configurations and jet behavior near TCs. Jets occur most commonly poleward of TCs within the 500–1000-km annulus, where TC outflow amplifies the background potential vorticity gradient. A rigorous clustering analysis is performed, resulting in statistically distinct clusters of jet traces that correspond to common configurations of large-scale flow near Atlantic TCs. The speed structure of westerly jets poleward of TCs is found to vary with location in the Atlantic basin, but acceleration of jets downstream of their closest approach to the TC due to interaction with the TC’s diabatic outflow is a consistent feature of these structures. In addition to the climatology developed here, this objectively constructed dataset of upper-tropospheric jets opens unique avenues for exploring TC–environment interactions and utilizing jets to quantitatively describe large-scale flow.

scholarly journals Vertical cloud structure of warm conveyor belts – a comparison and evaluation of ERA5 reanalysis, CloudSat and CALIPSO data

2020 ◽  
Vol 1 (2) ◽  
pp. 577-595
Author(s):  
Hanin Binder ◽  
Maxi Boettcher ◽  
Hanna Joos ◽  
Michael Sprenger ◽  
Heini Wernli
Keyword(s):  
Potential Vorticity ◽  
Lower Troposphere ◽  
Reanalysis Dataset ◽  
Large Variability ◽  
Cloud Structure ◽  
Melting Layer ◽  
Surface Precipitation ◽  
Conveyor Belts ◽  
Warm Conveyor Belts ◽  
Precipitating Clouds

Abstract. Warm conveyor belts (WCBs) are important cyclone-related airstreams that are responsible for most of the cloud and precipitation formation in the extratropics. They can also substantially influence the dynamics of cyclones and the upper-level flow. So far, most of the knowledge about WCBs is based on model data from analyses, reanalyses and forecast data with only a few observational studies available. The aim of this work is to gain a detailed observational perspective on the vertical cloud and precipitation structure of WCBs during their inflow, ascent and outflow and to evaluate their representation in the new ERA5 reanalysis dataset. To this end, satellite observations from the CloudSat radar and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) lidar are combined with an ERA5-based WCB climatology for nine Northern Hemisphere winters. Based on a case study and a composite analysis, the main findings can be summarized as follows. (i) WCB air masses are part of deep, strongly precipitating clouds, with cloud-top heights at 9–10 km during their ascent and an about 2–3 km deep layer with supercooled liquid water co-existing with ice above the melting layer. The maximum surface precipitation occurs when the WCB is at about 2–4 km height. (ii) Convective clouds can be observed above the inflow and during the ascent. (iii) At upper levels, the WCB outflow is typically located near the top of a 3 km deep cirrus layer. (iv) There is a large variability between WCBs in terms of cloud structure, peak reflectivity and associated surface precipitation. (v) The WCB trajectories with the highest radar reflectivities are mainly located over the North Atlantic and North Pacific, and – apart from the inflow – they occur at relatively low latitudes. They are associated with particularly deep and strongly precipitating clouds that occur not only during the ascent but also in the inflow and outflow regions. (vi) ERA5 represents the WCB clouds remarkably well in terms of position, thermodynamic phase and frozen hydrometeor distribution, although it underestimates the high ice and snow values in the mixed-phase clouds near the melting layer. (vii) In the lower troposphere, high potential vorticity is diabatically produced along the WCB in areas with high reflectivities and hydrometeor contents, and at upper levels, low potential vorticity prevails in the cirrus layer in the WCB outflow. The study provides important observational insight into the internal cloud structure of WCBs and emphasizes the ability of ERA5 to essentially capture the observed pattern but also reveals many small- and mesoscale structures observed by the remote sensing instruments but not captured by ERA5.

Lagrangian analysis of the dynamical and thermodynamic drivers of large-scale Greenland melt events during 1979-2017

2021 ◽  
Author(s):  
Mauro Hermann ◽  
Lukas Papritz ◽  
Heini Wernli
Keyword(s):  
Large Scale ◽  
Heat Waves ◽  
Lower Troposphere ◽  
Greenland Ice Sheet ◽  
Region Of Origin ◽  
Air Masses ◽  
Accumulation Zone ◽  
Warm Anomaly ◽  
Downward Longwave Radiation ◽  
The Impact

<p>We systematically investigate the dynamical and thermodynamic processes that lead to 77 large-scale melt events affecting high-elevation regions of the Greenland Ice Sheet (GrIS) in June-August (JJA) 1979-2017. For that purpose, we compute 8 day kinematic backward trajectories from the lowermost ~500 m above the GrIS. The key synoptic feature accompanying the melt events is an upper-tropospheric ridge over Southeast Greenland associated with a surface high-pressure system. This circulation pattern is favorable to induce rapid poleward transport (up to 40° latitude) of warm (~15 K warmer than climatological air masses arriving on the GrIS) and moist air masses from the lower troposphere to the western GrIS and subsequently to distribute them in the anticyclonic flow over north and east Greenland. During transport to the GrIS, the melt event air masses cool by ~15 K due to ascent and radiation, which keeps them just above the critical threshold to induce melting.</p><p>The thermodynamic analyses reveal that the final warm anomaly of the air masses is primarily owed to anomalous horizontal transport from a climatologically warm region of origin. However, before being transported to the GrIS, i.e., in their region of origin, these air masses were not anomalously warm. Latent heating from condensation of water vapor, occurring as the airstreams are forced to ascend orographically or dynamically, is of secondary importance. These characteristics were particularly pronounced during the most extensive melt event in early July 2012. In this event, importantly, the warm anomaly was not preserved from anomalously warm source regions such as North America experiencing a record heat wave. Considering the impact of moisture on the surface energy balance, we find that radiative effects are closely linked to the air mass trajectories and enhance melt over the entire GrIS accumulation zone due to (i) enhanced downward longwave radiation related to poleward moisture transport and a shift in the cloud phase from ice to liquid primarily west of the ice divide and (ii) increased shortwave radiation in clear-sky regions east of the ice divide.</p><p>The temporal evolution, positioning, and intensity of synoptic scale weather systems deserve further attention as they are responsible for strong and partly opposing atmospheric forcing of the GrIS surface mass balance. Also, the mechanisms identified here are in contrast to melt events in the low-elevation high Arctic and to midlatitude heat waves, where the upper-tropospheric ridge is essential to induce adiabatic warming by large-scale subsidence. Given the ongoing increase in the frequency and the melt extent of large-scale melt events, the understanding of upper-tropospheric ridges over the North Atlantic, i.e., also Greenland blocking, and its representation in climate models is crucial in determining future GrIS accumulation zone melt and thus global sea level rise. </p>

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