scholarly journals Increasing frequencies of warm and humid air masses over the conterminous United States from 1948 to 2005

2008 ◽  
Vol 35 (10) ◽  
Author(s):  
David B. Knight ◽  
Robert E. Davis ◽  
Scott C. Sheridan ◽  
David M. Hondula ◽  
Luke J. Sitka ◽  
...  
Keyword(s):  
United States ◽  
Humid Air ◽  
Air Masses

Dynamic and thermodynamic drivers of Arctic lower tropospheric warm extremes

2020 ◽  
Author(s):  
Lukas Papritz
Keyword(s):  
Storm Track ◽  
Lower Troposphere ◽  
High Arctic ◽  
Heat Fluxes ◽  
The Arctic ◽  
Sensible Heat ◽  
Humid Air ◽  
Secondary Importance ◽  
Air Masses ◽  
Diabatic Processes

<p align="justify">Recent decades have revealed dramatic changes in the high Arctic (> 80°N) related to natural variability and anthropogenic climate change. In particular, episodes of extremely warm temperatures in the lower troposphere and their role for sea ice melting have gained considerable attention. While it has been recognized that injections of warm and humid air masses contribute to wintertime warm anomalies, summertime warm anomalies have also been linked to blocking anticyclones within the high Arctic. Yet, the relative importance of the various thermodynamic and atmospheric dynamical processes that can contribute to the formation of extreme warm anomalies in the high Arctic is poorly understood.</p><p align="justify">In this work, we present a systematic analysis of the processes leading to the formation of winter- and summertime lower tropospheric warm extremes in the high Arctic by means of kinematic backward trajectories based on the ERA-Interim reanalysis. The trajectories enable us to quantify the relative contributions of poleward transport from (potentially) warmer regions, adiabatic warming due to subsidence, and diabatic heating associated with surface sensible heat fluxes and latent heat release. Furthermore, we relate these processes to atmospheric dynamical flow features such as atmospheric blocking and extratropical cyclones.</p><p align="justify">Our analyses reveal that subsidence in blocking anticyclones over the Barents and Kara Seas and diabatic warming by surface sensible heat fluxes are the dominant mechanisms leading to wintertime warm extremes (contributing about 40% each), whereas the transport from southerly latitudes – predominantly accomplished by the injection of warm and humid air masses associated with an intensified and westward displaced storm track in the Nordic Seas - is of secondary importance (20%). Summertime warm anomalies, in contrast, are essentially the result of subsidence in blocking anticyclones (70%) that are located within the high Arctic. Thus, our findings point towards a rich, seasonally varying spectrum of dynamical and thermodynamic processes contributing to Arctic warm extremes that result from a complex interplay between transport induced by dynamical weather systems and diabatic processes. Furthermore, they emphasize the importance of processes within the Arctic for the formation of warm extremes.</p><p align="justify">Papritz, L., 2019: Arctic lower tropospheric warm and cold extremes: horizontal and vertical transport, diabatic processes, and linkage to synoptic circulation features, <em>J. Climate</em>, doi: 10.1175/JCLI-D-19-0638.1</p>

Tornadoes in the Central United States and the “Clash of Air Masses”

2014 ◽  
Vol 95 (11) ◽  
pp. 1704-1712 ◽  
Author(s):  
David M. Schultz ◽  
Yvette P. Richardson ◽  
Paul M. Markowski ◽  
Charles A. Doswell
Keyword(s):  
United States ◽  
Air Masses ◽  
Central United States

Aerosol size distributions in air masses advecting off the east coast of the United States

1985 ◽  
Vol 90 (D1) ◽  
pp. 2365 ◽  
Author(s):  
William A. Hoppel ◽  
James W. Fitzgerald ◽  
Reginald E. Larson
Keyword(s):  
United States ◽  
East Coast ◽  
The United States ◽  
Size Distributions ◽  
Air Masses

scholarly journals Investigating the sources and atmospheric processing of fine particles from Asia and the Northwestern United States measured during INTEX B

2007 ◽  
Vol 7 (6) ◽  
pp. 17429-17474 ◽  
Author(s):  
R. E. Peltier ◽  
A. H. Hecobian ◽  
R. J. Weber ◽  
A. Stohl ◽  
E. L. Atlas ◽  
...  
Keyword(s):  
United States ◽  
North American ◽  
Fossil Fuel ◽  
Central Valley ◽  
Fuel Combustion ◽  
Water Soluble ◽  
Fossil Fuel Combustion ◽  
Air Masses ◽  
Water Soluble Organic Carbon ◽  
Soluble Organic Carbon

Abstract. During the National Aeronautics and Space Administration (NASA) Intercontinental Chemical Transport Experiment, Phase B (INTEX-B), in the spring of 2006, airborne measurements were made in the United States Pacific Northwest of the major inorganic ions and the water-soluble organic carbon (WSOC) of submicron (PM1.0) aerosol. An atmospheric trajectory (Hysplit) and a Lagrangian particle dispersion model (Flexpart) quantifying source contributions for carbon monoxide (CO) was used to segregate air masses into those of primarily Asian influence (>75% Asian CO) or North American influence (>75% North American CO). Of the measured compounds, fine particle mass mostly consisted of water-soluble organic carbon and sulfate, with highest median WSOC and sulfate concentrations in North American air masses. The fraction of WSOC to sulfate was significantly lower than one at altitudes above 3 km, opposite to what has been observed closer to Asia and in the northeastern United States, where organic components were at higher concentrations than sulfate in the free troposphere. The observations could be explained by loss of sulfate and organic aerosol due to precipitation scavenging, with reformation of mainly sulfate during advection from Asia to North America. WSOC sources were investigated by multivariate linear regression analyses of WSOC and volatile organic compounds (VOCs). In Asian air masses, of the WSOC variability that could be explained (49%), most were related to fossil fuel combustion VOCs, compared to North American air masses, where 75% of the WSOC variability was explained through a nearly equal combination of fossil fuel combustion and biogenic VOCs. Distinct WSOC plumes encountered during the experiment were also studied. A plume observed near the California Central Valley at 0.6 km altitude was related to both fossil fuel combustion and biogenic VOCs. Another Central Valley plume observed over Nevada at 3 to 5 km, in a region of cloud detrainment, was mostly related to biogenic VOCs.

scholarly journals Protection against lightning on the geomagnetic observatory

2014 ◽  
Vol 4 (1) ◽  
pp. 213-234
Author(s):  
R. Čop ◽  
G. Milev ◽  
D. Deželjin ◽  
J. Kosmač
Keyword(s):  
Electrical Charge ◽  
Secondary Effects ◽  
Geomagnetic Observatory ◽  
Humid Air ◽  
Air Masses ◽  
Thunderstorm Cloud ◽  
Short Time

Abstract. The Sinji Vrh Geomagnetic Observatory was built on the brow of the mountain Gora, above Ajdovščina, and all over Europe one may hardly find an area which is more often struck by lightning than this south-western part of Slovenia. When the humid air masses of a storm front hit the edge of Gora, they rise up more than 1000 m in a very short time, and this causes the additional electrical charge of stormy clouds. The reliability of operations performed in the every building of observatory could be increased by understanding the formation of lightning in the thunderstorm cloud, the application of already proven methods of protection against a strike of lightning and against its secondary effects. To reach this goal the following groups of experts have to co-operate: the experts in the field of protection against lightening phenomenon, the constructors and manufacturers of equipment and the observatory managers.

scholarly journals Detecting moisture transport pathways to the subtropical North Atlantic free troposphere using paired H<sub>2</sub>O-<i>δ</i>D in situ measurements

2016 ◽  
Vol 16 (7) ◽  
pp. 4251-4269 ◽  
Author(s):  
Yenny González ◽  
Matthias Schneider ◽  
Christoph Dyroff ◽  
Sergio Rodríguez ◽  
Emanuel Christner ◽  
...  
Keyword(s):  
North Atlantic ◽  
In Situ Measurements ◽  
Back Trajectory ◽  
Free Troposphere ◽  
Night Time ◽  
Humid Air ◽  
Transport Pathways ◽  
Air Masses ◽  
Dry Convection

Abstract. We present two years of in situ measurements of water vapour (H2O) and its isotopologue ratio (δD, the standardized ratio between H216O and HD16O), made at two remote mountain sites on Tenerife in the subtropical North Atlantic. We show that the data – if measured during night-time – are well representative for the lower/middle free troposphere. We use the measured H2O-δD pairs, together with dust measurements and back trajectory modelling for analysing the moisture pathways to this region. We can identify four principally different transport pathways. The air mass transport from high altitudes and high latitudes shows two different scenarios. The first scenario brings dry air masses to the stations, as the result of condensation events occurring at low temperatures. The second scenario brings humid air masses to the stations, due to cross-isentropic mixing with lower-level and more humid air during transport since last condensation (LC). The third pathway is transportation from lower latitudes and lower altitudes, whereby we can identify rain re-evaporation as an occasional source of moisture. The fourth pathway is linked to the African continent, where during summer, dry convection processes over the Sahara very effectively inject humidity from the boundary layer to higher altitudes. This so-called Saharan Air Layer (SAL) is then advected westward over the Atlantic and contributes to moisten the free troposphere. We demonstrate that the different pathways leave distinct fingerprints on the measured H2O-δD pairs.

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