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Fernando Martín
,
Sylvia N. Crespí
, and
Magdalena Palacios

Abstract

The Topography Vorticity-Mode Mesoscale (TVM) model has been evaluated for four different cases of thermal low pressure systems over the Iberian Peninsula. These conditions are considered to be representative of the range of summer thermal low pressure conditions in this region. Simulation results have been compared with observations obtained in two intensive experimental campaigns carried out in the Greater Madrid Area in the summer of 1992. The wind fields are qualitatively well simulated by the model. Detailed comparisons of the time series of simulations and observations have been carried out at several meteorological stations. For wind speed and direction, TVM results are reasonably good, although an underprediction of the daily thermal oscillation has been detected. The model reproduces the observed decoupled flow in the nighttime and early morning along with the evolution of mixing layer flow during the day. In addition, the model has simulated specific features of the observed circulations such as low-level jets and drainage, downslope, upslope, and upvalley flows. The model also simulates the formation of hydrostatic mountain waves in the nighttime in some cases.

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Fernando Martín
,
Magdalena Palacios
, and
Sylvia N. Crespí

Abstract

This paper discusses the variability of air-parcel transport under similar summer thermal low pressure conditions over the Iberian Peninsula. Three-dimensional trajectories were estimated by means of the Topography Vorticity-Mode Mesoscale model. Four cases of the 1992 summer thermal low pressure system have been considered, covering most of the variability of this synoptic meteorological situation.

Transport patterns were very different among the four studied cases. Results indicate that synoptic wind forcing can influence trajectories under thermal low conditions. It was found that a remarkable difference exists between the transport of air parcels released at low levels, which are affected by thermally driven flows, and those released at higher levels, which are more influenced by the synoptic wind. Moreover, potentially polluted air parcels (released in the daytime) travel farther than the potentially nonpolluted ones (released at night) in the case of lower-level releases. In addition, important differences between the transport patterns of polluted morning air parcels and polluted afternoon air parcels are detected and discussed.

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Michael Hill
,
Ron Calhoun
,
H. J. S. Fernando
,
Andreas Wieser
,
Andreas Dörnbrack
,
Martin Weissmann
,
Georg Mayr
, and
Robert Newsom

Abstract

Dual-Doppler analysis of data from two coherent lidars during the Terrain-Induced Rotor Experiment (T-REX) allows the retrieval of flow structures, such as vortices, during mountain-wave events. The spatial and temporal resolution of this approach is sufficient to identify and track vortical motions on an elevated, cross-barrier plane in clear air. Assimilation routines or additional constraints such as two-dimensional continuity are not required. A relatively simple and quick least squares method forms the basis of the retrieval. Vortices are shown to evolve and advect in the flow field, allowing analysis of their behavior in the mountain–wave–boundary layer system. The locations, magnitudes, and evolution of the vortices can be studied through calculated fields of velocity, vorticity, streamlines, and swirl. Generally, observations suggest two classes of vortical motions: rotors and small-scale vortical structures. These two structures differ in scale and behavior. The level of coordination of the two lidars and the nature of the output (i.e., in range gates) creates inherent restrictions on the spatial and temporal resolution of retrieved fields.

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Federico Bianchi
,
Victoria A. Sinclair
,
Diego Aliaga
,
Qiaozhi Zha
,
Wiebke Scholz
,
Cheng Wu
,
Liine Heikkinen
,
Rob Modini
,
Eva Partoll
,
Fernando Velarde
,
Isabel Moreno
,
Yvette Gramlich
,
Wei Huang
,
Alkuin Maximilian Koenig
,
Markus Leiminger
,
Joonas Enroth
,
Otso Peräkylä
,
Angela Marinoni
,
Chen Xuemeng
,
Luis Blacutt
,
Ricardo Forno
,
Rene Gutierrez
,
Patrick Ginot
,
Gaëlle Uzu
,
Maria Cristina Facchini
,
Stefania Gilardoni
,
Martin Gysel-Beer
,
Runlong Cai
,
Tuukka Petäjä
,
Matteo Rinaldi
,
Harald Saathoff
,
Karine Sellegri
,
Douglas Worsnop
,
Paulo Artaxo
,
Armin Hansel
,
Markku Kulmala
,
Alfred Wiedensohler
,
Paolo Laj
,
Radovan Krejci
,
Samara Carbone
,
Marcos Andrade
, and
Claudia Mohr

Abstract

This paper presents an introduction to the Southern Hemisphere High Altitude Experiment on Particle Nucleation and Growth (SALTENA). This field campaign took place between December 2017 and June 2018 (wet to dry season) at Chacaltaya (CHC), a GAW (Global Atmosphere Watch) station located at 5,240 m MSL in the Bolivian Andes. Concurrent measurements were conducted at two additional sites in El Alto (4,000 m MSL) and La Paz (3,600 m MSL). The overall goal of the campaign was to identify the sources, understand the formation mechanisms and transport, and characterize the properties of aerosol at these stations. State-of-the-art instruments were brought to the station complementing the ongoing permanent GAW measurements, to allow a comprehensive description of the chemical species of anthropogenic and biogenic origin impacting the station and contributing to new particle formation. In this overview we first provide an assessment of the complex meteorology, airmass origin, and boundary layer–free troposphere interactions during the campaign using a 6-month high-resolution Weather Research and Forecasting (WRF) simulation coupled with Flexible Particle dispersion model (FLEXPART). We then show some of the research highlights from the campaign, including (i) chemical transformation processes of anthropogenic pollution while the air masses are transported to the CHC station from the metropolitan area of La Paz–El Alto, (ii) volcanic emissions as an important source of atmospheric sulfur compounds in the region, (iii) the characterization of the compounds involved in new particle formation, and (iv) the identification of long-range-transported compounds from the Pacific or the Amazon basin. We conclude the article with a presentation of future research foci. The SALTENA dataset highlights the importance of comprehensive observations in strategic high-altitude locations, especially the undersampled Southern Hemisphere.

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