scholarly journals Raco Wind at the Exit of the Maipo Canyon in Central Chile: Climatology, Special Observations, and Possible Mechanisms

2020 ◽  
Vol 59 (4) ◽  
pp. 725-749 ◽  
Author(s):  
Ricardo C. Muñoz ◽  
Laurence Armi ◽  
José A. Rutllant ◽  
Mark Falvey ◽  
C. David Whiteman ◽  
...  
Keyword(s):  
Cold Season ◽  
Complete Characterization ◽  
Cold Pool ◽  
Valley Wind ◽  
Central Chile ◽  
Synoptic Conditions ◽  
Drying Up ◽  
Surface Measurements ◽  
Dry Down ◽  
Sudden Appearance

AbstractRaco is the local name given to a strong (gusts up to 17 m s−1), warm, and dry down-valley wind observed at the exit of the Maipo River Canyon in central Chile. Its climatology is documented based on eight years of surface measurements near the canyon exit together with a more complete characterization of its structure during an intensive observational period (IOP) carried out in July 2018. Raco winds occur in the cold season under well-defined synoptic conditions, beginning abruptly at any time during the night, reaching maximum hourly averages around 10 m s−1, and terminating around noon with the onset of afternoon westerly up-valley winds. About 25% of the days in May–August have more than six raco hours between 0100 and 1200 LT, and raco episodes last typically 1–2 days. The sudden appearance of raco winds at the surface can be accompanied by conspicuous warming (up to 10°C) and drying (up to 3 g kg−1). Raco winds are associated with a strong along-canyon pressure gradient, a regional pressure fall, and clear skies. During the IOP, radiosondes launched from both extremes of the canyon exit corridor showed a nocturnal easterly jet at 700 m AGL that occasionally descended rapidly to the surface, producing the raco. Transects along the canyon performed with a mobile ceilometer revealed a sharp frontlike feature between the cold pool over the Santiago Valley and the raco-affected conditions in the Maipo Canyon. Possible factors producing the easterly jet aloft and its occasional descent toward the surface are discussed, and a gap-wind mechanism is postulated to be at work.

Description of Wind Field Dynamic Patterns in a Valley and Their Relation to Mesoscale and Synoptic-Scale Meteorological Situations

1995 ◽  
Vol 34 (1) ◽  
pp. 49-67 ◽  
Author(s):  
R. Guardans ◽  
I. Palomino
Keyword(s):  
Wind Field ◽  
Transition Probabilities ◽  
Meteorological Data ◽  
Atmospheric Dispersion ◽  
Synoptic Situation ◽  
Large Set ◽  
Valley Wind ◽  
Complete Collection ◽  
Emergency Plans ◽  
Synoptic Conditions

Abstract A large set of hourly meteorological data from seven towers deployed in Montesina Valley (Cordoba, Spain) is studied in relation to the prevailing synoptic situation. The complete collection of daily synoptic maps for 1985-90 has been classified in seven basic weather patterns. First-order transition probabilities and weatherpattern persistences have been calculated for each of the patterns. The behavior of the local valley wind field is described as a function of the synoptic patterns. The work reported here, based on observations of the characteristic time and space patterns of flow in the valley under different synoptic conditions, has made it possible to obtain a set of empirical rules and regression functions to produce forecasts of the local wind field as a function of the synoptic situation and the hour of the day to be used in the emergency plans. The result of this work is currently being implemented in an atmospheric dispersion module of an expert system that will be used as a tool to predict the evolution of accidental and routine hazardous emissions to the atmosphere in complex terrain such as valleys and coastal areas.

scholarly journals Thermally Driven Flows at an Asymmetric Valley Exit: Observations and Model Studies at the Lech Valley Exit

2009 ◽  
Vol 137 (10) ◽  
pp. 3437-3455 ◽  
Author(s):  
Thomas Spengler ◽  
Jan H. Schween ◽  
Markus Ablinger ◽  
Günther Zängl ◽  
Joseph Egger
Keyword(s):  
Shear Zone ◽  
Weather Conditions ◽  
Western Slope ◽  
Eastern Slope ◽  
Valley Wind ◽  
Model Studies ◽  
Synoptic Conditions ◽  
Thermally Driven ◽  
The Alps ◽  
Alpine Foreland

Abstract The summertime thermal circulation in the region of an asymmetric valley exit is investigated by means of observations and high-resolution model simulations. The northeastward-oriented Alpine Lech Valley opening into the Bavarian Alpine foreland has an eastern slope exceeding the western slope by about 15 km. Northerly winds along the eastern slope are frequently observed, reaching substantial strength during fair weather conditions. A field experiment has been conducted to explore this phenomenon and to pinpoint the connection of the northeasterly flow to the Lech Valley wind circulation. Numerical simulations have also been carried out to support the interpretation of the observations. It is found that the northerlies owe their existence to the dominantly easterly flow along the foothills of the Alps, which is partly induced by the Alpine heat low but may be strengthened by favorable synoptic conditions. Examples for both situations will be discussed. The diurnal flow in the Lech Valley has little obvious impact on these northeasterlies. On days with moderate synoptic easterly flow, a wake is present on the lee of the eastern slope of the exit region, accompanied by a shear zone along the edge of the wake. This shear zone is forced southward during the daytime because of thermally initiated pressure gradients between the Alpine foreland and the Alps, leading to sudden wind changes in the exit area at the time of its passage.

scholarly journals The anomalous high temperatures of November 2010 over Greece: meteorological and climatological aspects

2011 ◽  
Vol 11 (10) ◽  
pp. 2705-2714 ◽  
Author(s):  
K. Tolika ◽  
I. Pytharoulis ◽  
P. Maheras
Keyword(s):  
High Temperatures ◽  
Climate Models ◽  
Eastern Mediterranean ◽  
Regional Climate ◽  
Simulated Data ◽  
Regional Climate Models ◽  
Cold Season ◽  
Maximum Temperature ◽  
The Caspian Sea ◽  
Synoptic Conditions

Abstract. This paper presents an analysis of the exceptionally high maximum (Tmax) and minimum (Tmin) temperatures which occurred during November 2010 and affected the entire Greek region. This severe "warm cold-season spell" was unusual because of its prolonged duration and intensity for the entire month and particularly the maximum temperature anomalies, which in comparison with the 1958–2000 climatological average, exceeded 5 °C at several stations. Comparing the observed record with future projections from three regional climate models revealed that Tmax and Tmin, on several days in November 2010, exceeded the 90th percentile of the simulated data. An examination of the atmospheric – synoptic conditions during this period showed that the anomalous high temperatures could probably be related to the negative phase of the Eastern Mediterranean Pattern (EMP), with an intense pole of negative anomalies located over the British Isles, and to the east, a second pole of positive anomalies, centred over the Caspian Sea. Finally, an attempt is made to further investigate the mechanisms responsible for this phenomenon, for example, the thermal forcing in the tropics (Niño 3 or Niño 3.4).

scholarly journals Analysis of the diurnal development of a lake-valley circulation in the Alps based on airborne and surface measurements

2014 ◽  
Vol 14 (18) ◽  
pp. 9771-9786 ◽  
Author(s):  
L. Laiti ◽  
D. Zardi ◽  
M. de Franceschi ◽  
G. Rampanelli ◽  
L. Giovannini
Keyword(s):  
Radiative Forcing ◽  
Potential Temperature ◽  
Surface Wind ◽  
Valley Floor ◽  
Valley Wind ◽  
Near Surface ◽  
Early Afternoon ◽  
Downslope Wind ◽  
Surface Measurements ◽  
Mixed Layers

Abstract. This study investigates the thermal structures of the atmospheric boundary layer (ABL) and the near-surface wind field associated with a lake-valley circulation in the south-eastern Italian Alps – the so-called Ora del Garda. Two flights of an equipped motorglider allowed for the exploration of the diurnal evolution of this circulation, from the onset, on Lake Garda's shoreline, throughout its development along the Sarca Valley and Lakes Valley (Valle dei Laghi), to the outflow into the Adige Valley. At the same time, surface observations, both from a targeted field campaign and from routinely operated weather stations, supported the analysis of the development of the Ora del Garda at the valley floor. In particular, in the valleys typical ABL vertical structures, characterized by rather shallow convective mixed layers (~ 500 m) and (deeper) weakly stable layers above, up to the lateral crest height, are identified in the late morning. In contrast, close to the lake the ABL is stably stratified down to very low heights, as a consequence of the intense advection of colder air associated with the Ora del Garda flow (up to 6 m s–1). The combined analysis of surface and airborne observations (remapped over 3-D high-resolution grids) suggests that the lake-breeze front propagating up-valley from the shoreline in the late morning penetrates slightly later at the eastern end of the valley inlet (delay: ~ 1 h), probably due to the asymmetric radiative forcing caused by the N–S valley orientation. On the other hand, in the early afternoon the Ora del Garda overflows through an elevated gap, producing an anomalous, strong cross-valley wind (5 m s–1) at the Adige Valley floor north of Trento, which overwhelms the local up-valley wind. This feature is associated with a strong deepening of the local mixed layer (from 400 to 1300 m). The potential temperature 3-D field suggests that the intense turbulent mixing may be attributed to the development of a downslope wind across the gap, followed by a hydraulic jump downstream.

scholarly journals Polar Lows over the Nordic Seas: Improved Representation in ERA-Interim Compared to ERA-40 and the Impact on Downscaled Simulations

2014 ◽  
Vol 142 (6) ◽  
pp. 2271-2289 ◽  
Author(s):  
Thibaut Laffineur ◽  
Chantal Claud ◽  
Jean-Pierre Chaboureau ◽  
Gunnar Noer
Keyword(s):  
Barents Sea ◽  
Mesoscale Model ◽  
Cold Season ◽  
Small Scale ◽  
Polar Lows ◽  
Wind Speeds ◽  
Short Life Span ◽  
Synoptic Conditions ◽  
Polar Low ◽  
The Impact

Abstract Polar lows are intense high-latitude mesocyclones that form during the cold season over open sea. Their relatively small-scale and short life span lead to a rather poor representation in model outputs and meteorological reanalyses. In this paper, the ability of the Interim European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-Interim) to represent polar lows over the Norwegian and Barents Sea is assessed, and a comparison with the 40-yr ECMWF Re-Analysis (ERA-40) is provided for three cold seasons (1999–2000 until 2001–02). A better representation in ERA-Interim is found, with 13 systems captured out of the 29 observed, against 6 in the case of ERA-40. Reasons for the lack of representation are identified. Unexpectedly, the representation of different polar low sizes does not appear to be linked to the resolution. Rather, it is the representation of synoptic conditions that appears to be essential. In a second part, a downscaling is conducted using the mesoscale model Méso-NH. For each observed polar low, a pair of simulations is performed: one initialized by ERA-Interim and the other one by ERA-40. An improvement is noted with 22 polar lows represented when ERA-Interim is used. Through a model-to-satellite approach, it is shown that even if polar lows are simulated, convective processes remain insufficiently represented. Wind speeds, which were underestimated in reanalyses, are nevertheless more realistic in the Méso-NH simulations. These results are supported by a spectral analysis of reanalyses and Méso-NH fields.

scholarly journals Spatial Distribution And Synoptic Conditions Of Snow Accumulation And Snow Ablation In The West Siberian Plain

2015 ◽  
Vol 34 (3) ◽  
pp. 5-15 ◽  
Author(s):  
Ewa Bednorz ◽  
Joanna Wibig
Keyword(s):  
Sea Level ◽  
Cold Season ◽  
Snow Accumulation ◽  
West Siberian Plain ◽  
The West ◽  
Sea Level Pressure ◽  
Level Pressure ◽  
The North ◽  
Synoptic Conditions ◽  
Air Circulation

Abstract The mean duration of snow coverage in the West Siberian Plain is approximately eight months in the north to about five months in the south. While the period of intense snow melting is short (one or two months between March and May), snow accumulation persists for most of the cold season. Snow accumulation is associated with negative anomalies of sea level pressure, which means increased cyclonal activity and weaker than normal Siberian High. Much lower anomalies of sea level pressure occur during snow ablation. This suggests smaller influence of air circulation on snow cover reduction in spring.

scholarly journals A Study of Two Propagating Heavy-Rainfall Episodes near Taiwan during SoWMEX/TiMREX IOP-8 in June 2008. Part I: Synoptic Evolution, Episode Propagation, and Model Control Simulation

2014 ◽  
Vol 142 (8) ◽  
pp. 2619-2643 ◽  
Author(s):  
Chung-Chieh Wang ◽  
Jason Chieh-Sheng Hsu ◽  
George Tai-Jen Chen ◽  
Dong-In Lee
Keyword(s):  
Heavy Rainfall ◽  
Rapid Development ◽  
Regional Scale ◽  
Vertical Shear ◽  
Squall Line ◽  
Cold Pool ◽  
First Episode ◽  
Low Level ◽  
Model Control ◽  
Synoptic Conditions

Abstract This paper is the first of a two-part study to investigate two rain-producing episodes in the longitude–time (Hovmöller) space upstream from Taiwan during the eighth intensive observing period (IOP-8, 12–17 June 2008) of the Southwest Monsoon Experiment/Terrain-influenced Monsoon Rainfall Experiment (SoWMEX/TiMREX), with a goal to better understand the mechanism and controlling factors for their organization and propagation. Both in a prefrontal environment, the first episode moved eastward and the second was a rare westward-moving event, and each caused heavy rainfall in Taiwan, on 14 and 16 June, respectively. In Part II, the roles played by synoptic conditions and terrain effects are further examined through sensitivity tests. With the aid from a successful simulation with a grid spacing of 2.5 km, the structure and organization of convection embedded in the two episodes are shown to be different. With stronger low-level vertical wind shear in its environment, the first episode consisted of well-organized squall-line-type convective systems and propagated eastward mainly through cold-pool dynamics. However, the convection of the second episode was scattered and less organized with weaker vertical shear, and individual cells traveled with background flow toward the north-northeast. Throughout the 6-day case period, the southwesterly low-level jet (LLJ) is found to have much control over the general region of convection, and thus dictates the overall rainfall pattern in the Hovmöller space at the regional scale. The rapid development of the mei-yu front and LLJ over southeastern China during 16–17 June, to the west of the previous location of the jet, is found to result in the westward movement of the second episode.

scholarly journals NOx AND O3 VARIABILITY AND ITS RELATION WITH WEATHER CONDITIONS IN IAȘI CITY

2019 ◽  
Vol 13 (2) ◽  
pp. 69-85
Author(s):  
Vlad-Alexandru AMIHĂESEI ◽  
Lucian SFÎCĂ ◽  
Liviu APOSTOL ◽  
Alina LEAHU
Keyword(s):  
Surface Ozone ◽  
Atmospheric Stability ◽  
Warm Season ◽  
Weather Conditions ◽  
Cold Season ◽  
Atmospheric Pollutants ◽  
Oxides Of Nitrogen ◽  
Atmospheric Conditions ◽  
Synoptic Conditions ◽  
Radiation Maximum

The paper presents the temporal variability of surface ozone (O3) and its precursors (oxides of nitrogen - NOx) from January 2012 to December 2015. In the same time, this study is aimed to explore the influence of the weather elements on these two major atmospheric pollutants in the area of Iași city. The maximum record of nitrogen oxides reached during the 4 analyzed years was 1200 μ/m-3 on October 27, 2015, a period of the year when atmospheric stability prevails. During the warm season (considered from May to September) the highest concentration of ozone was recorded at 155 μ/m-3. The winds direction from SSE or NNW and the winds speed greater than 2 m/s can significantly increase the concentration of the O3 and NOx respectively. Also, the stable atmospheric conditions can increase especially the concentration of the nitrogen dioxides. The statistical results illustrate a strong Pearson's correlation of surface ozone with solar radiation/maximum air temperature (r >0.5). The correlations were strongest during the summer months. Using the composite method, between warm season and cold season a difference of the pollutants concentration greater than 30 units for NOx was observed. Synoptic conditions associated with high pollution are also described.

scholarly journals Central European Blocking Anticyclones and the Influences Imprint over the Romania’s Climate

2016 ◽  
Vol 10 (2) ◽  
pp. 235-248
Author(s):  
Niţă Andrei ◽  
Apostol Liviu
Keyword(s):  
Central Europe ◽  
Cold Season ◽  
Climatic Conditions ◽  
Average Period ◽  
British Isles ◽  
Synoptic Classification ◽  
Central European ◽  
Synoptic Conditions ◽  
Maximum Temperatures ◽  
Output Volume

Abstract Blocking anticyclonic circulations from Europe are provoking climatic episodes responsible for discomfort, human and financial loses. During the summer, these episodes are known for prolonged droughts and maximum temperatures often exceeding 35 °C to 40 °C. In the cold season, the rainfalls are close to 0 while the daily minimum temperatures are low under the average period. For this study, we used a synoptic classification which is available especially for Central Europe but works similarly for Romanian territory too. We aim to follow what kind of climatic conditions these circulations are producing in Romania during their presence in Europe. ECA&D daily gridded climatic dataset was used in this study. The study period lasts from 1961 to 2012. We used the minimum and maximum daily temperatures as well the rainfall quantities recorded. Since the output volume of data was too high, we aggregated the results into yearly multiseasonal average. In order to classify the synoptic patterns as blocking anticyclones, we used two synoptic situations from Hess-Brezowsky defined as Anticyclone High Central (HM) and High British Isles (HB). We calculated the thermic anomalies as well the rainfall quantities recorded in Romania during the presence of these circulations in central Europe. The results shows a perspective over the synoptic conditions in Romania during the presence of the above mentioned synoptic types in Central Europe.

scholarly journals Influence of macroscale and regional circulation patterns on low- and high-frequency sea level variability in the Baltic Sea

2021 ◽  
Author(s):  
Ewa Bednorz ◽  
Arkadiusz M. Tomczyk
Keyword(s):  
Baltic Sea ◽  
Sea Level ◽  
North Atlantic ◽  
Cold Season ◽  
The Baltic Sea ◽  
Sea Level Variability ◽  
The North ◽  
Synoptic Conditions ◽  
The North Atlantic ◽  
The Baltic

AbstractThe atmospheric impact on sea level variability in the Baltic Sea on different time scales was investigated. The Northern Hemisphere teleconnection patterns, namely, the North Atlantic Oscillation (NAO), Arctic Oscillation (AO) and Scandinavia (SCAND) patterns, were employed, and a strong but non-stationary relationship was found. The SCAND appeared to be most relevant to the mean monthly Baltic Sea level variations throughout the year. A negative correlation indicates that a cyclonic centre over Scandinavia in the negative phase of SCAND enhances western circulation, which then triggers water inflow through the Danish straits. The AO annular mode reveals a positive and slightly stronger relationship with the Baltic Sea level than the NAO. The rapid increases in the Baltic Sea level recognized in this study, namely, those exceeding 24 cm within a 5-day period, mainly occur in the cold season. These increases are associated with the development of specific synoptic conditions in the Euro-Atlantic region, characterized by a shift from high to low pressure over Europe and a rapid increase in the pressure gradient during the week preceding the sea level rise. Rapid increases are associated with cyclones coming from the North Atlantic, which move 1500–2000 km during the week preceding the strong rise of the Baltic waters. The cyclone tracks may be shifted north or south, while the final position is over the Norwegian Sea.

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