Synoptic and Mesoscale atmospheric features associated with an extreme Snowstorm over the Central Andes in August 2013

Abstract. We study the synoptic and mesoscale characteristics of a snowfall event over the Bolivian Altiplano in August 2013 that caused severe damage to people, infrastructure and livestock. This event was associated with a cold front episode following the eastern slope of the Andes-Amazon interface and a cut-off low pressure system (COL) over the Pacific Ocean. Large scale analyses suggest a two-stage mechanism: The first phase consisted of a strong cold surge to the east of the Andes inducing low level blocking of southward moisture transport over the SW Amazon basin due to post-frontal high-pressure up to 500 hPa synchronized to a Rossby wave train. The second stage was initiated by the displacement of 500 hPa anticyclone over the Andes due to a Rossby wave passage and a subsequent increase in north-easterly moisture transport, while another cold front along the eastern Andes provided additional lifting. We analyse an analog event (July 2010) to confirm the influence of these large-scale features on snow formation. We conduct a mesoscale analysis using the Weather Research and Forecasting (WRF-ARW) model. For this purpose, we perform a series of high-resolution numerical experiments that include sensitivity studies where we apply orographic and lake Titicaca temperature modifications. We compare our findings to MODIS snow cover estimates and in-situ measurements. The control simulation is able to capture the snow cover spatial distribution and sheds light over several aspects of the snowfall dynamics. In our WRF simulations, daytime snowfall mainly occurs around complex orography whereas nocturnal snowfall is concentrated over the plateau due to a combination of nocturnal winds and complex orography inside the plateau. The sensitivity experiments indicate the importance of the lake and mountain for thermal wind circulation affecting the spatial distribution of snowfall by shifting the position of the convergence zones. The influence of the lake's thermal effect is not evident around the regions surrounding the lake.

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Spatial impact and triggering conditions of the exceptional hydro-geomorphological event of December 1909 in Iberia

Natural Hazards and Earth System Science ◽

10.5194/nhess-16-371-2016 ◽

2016 ◽

Vol 16 (2) ◽

pp. 371-390 ◽

Cited By ~ 14

Author(s):

S. Pereira ◽

A. M. Ramos ◽

J. L. Zêzere ◽

R. M. Trigo ◽

J. M. Vaquero

Keyword(s):

Spatial Distribution ◽

Iberian Peninsula ◽

Large Scale ◽

Extreme Event ◽

Social Impacts ◽

Meteorological Conditions ◽

Pressure System ◽

Data Set ◽

Upper Level ◽

Disaster Event

Abstract. According to the DISASTER database the 20–28 December 1909 event was the hydro-geomorphologic event with the highest number of flood and landslide cases that occurred in Portugal in the period 1865–2010 (Zêzere et al., 2014). This event also caused important social impacts over the Spanish territory, especially in the Douro Basin, having triggered the highest floods in more than 100 years at the river's mouth in the city of Oporto. This work has a dual purpose: (i) to characterize the spatial distribution and social impacts of the December 1909 hydro-geomorphologic DISASTER event over Portugal and Spain; (ii) to analyse the meteorological conditions that triggered the event and the spatial distribution of the precipitation anomalies. Social impacts that occurred in Portugal were obtained from the Disaster database (Zêzere et al., 2014) whereas the data collection for Spain was supported by the systematic analysis of Spanish daily newspapers. In addition, the meteorological conditions that triggered the event are analysed using the 20th Century Reanalysis data set from NOAA and precipitation data from Iberian meteorological stations. The Iberian Peninsula was spatially affected during this event along the SW-NE direction spanning from Lisbon, Santarém, Oporto, and Guarda (in Portugal), to Salamanca, Valladolid, Zamora, Orense, León, and Palencia (in Spain). In Iberia, 134 DISASTER cases were recorded (130 flood cases; 4 landslides cases) having caused 89 casualties (57 due to floods and 32 due to landslides) and a further total of 3876 affected people, including fatalities, injured, missing, evacuated, and homeless people. This event was associated with outstanding precipitation registered at Guarda (Portugal) on 22 December 1909 and unusual meteorological conditions characterized by the presence of a deep low-pressure system located over the NW Iberian Peninsula with a stationary frontal system striking the western Iberian Peninsula. The presence of an upper-level jet (250 hPa) and low-level jet (900 hPa) located SW–NE oriented towards Iberia along with upper-level divergence and lower-level convergence favoured large-scale precipitation. Finally, associated with these features it is possible to state that this extreme event was clearly associated with the presence of an elongated Atmospheric River, crossing the entire northern Atlantic Basin and providing a continuous supply of moisture that contributed to enhance precipitation. This work contributes to a comprehensive and systematic synoptic evaluation of the second most deadly hydro-geomorphologic DISASTER event that has occurred in Portugal since 1865 and will help to better understand the meteorological system that was responsible for triggering the event.

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Tropical Cyclogenesis Associated with Rossby Wave Energy Dispersion of a Preexisting Typhoon. Part I: Satellite Data Analyses*

Journal of the Atmospheric Sciences ◽

10.1175/jas3692.1 ◽

2006 ◽

Vol 63 (5) ◽

pp. 1377-1389 ◽

Cited By ~ 70

Author(s):

Tim Li ◽

Bing Fu

Keyword(s):

Rossby Wave ◽

Satellite Data ◽

Wave Energy ◽

Large Scale ◽

Wave Train ◽

Vertical Shear ◽

Energy Dispersion ◽

Data Analyses ◽

Wave Trains ◽

Rossby Wave Train

Abstract The structure and evolution characteristics of Rossby wave trains induced by tropical cyclone (TC) energy dispersion are revealed based on the Quick Scatterometer (QuikSCAT) and Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) data. Among 34 cyclogenesis cases analyzed in the western North Pacific during 2000–01 typhoon seasons, six cases are associated with the Rossby wave energy dispersion of a preexisting TC. The wave trains are oriented in a northwest–southeast direction, with alternating cyclonic and anticyclonic vorticity circulation. A typical wavelength of the wave train is about 2500 km. The TC genesis is observed in the cyclonic circulation region of the wave train, possibly through a scale contraction process. The satellite data analyses reveal that not all TCs have a Rossby wave train in their wakes. The occurrence of the Rossby wave train depends to a certain extent on the TC intensity and the background flow. Whether or not a Rossby wave train can finally lead to cyclogenesis depends on large-scale dynamic and thermodynamic conditions related to both the change of the seasonal mean state and the phase of the tropical intraseasonal oscillation. Stronger low-level convergence and cyclonic vorticity, weaker vertical shear, and greater midtropospheric moisture are among the favorable large-scale conditions. The rebuilding process of a conditional unstable stratification is important in regulating the frequency of TC genesis.

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The 2010 Pakistan Flood and Russian Heat Wave: Teleconnection of Hydrometeorological Extremes

Journal of Hydrometeorology ◽

10.1175/jhm-d-11-016.1 ◽

2012 ◽

Vol 13 (1) ◽

pp. 392-403 ◽

Cited By ~ 187

Author(s):

William K. M. Lau ◽

Kyu-Myong Kim

Keyword(s):

Heat Wave ◽

Rossby Wave ◽

Large Scale ◽

Wave Train ◽

Intraseasonal Oscillation ◽

Heavy Rain ◽

Atmospheric Blocking ◽

Surface Energy Fluxes ◽

Upper Level ◽

Rain Events

Abstract In this paper, preliminary results are presented showing that the two record-setting extreme events during 2010 summer (i.e., the Russian heat wave–wildfires and Pakistan flood) were physically connected. It is found that the Russian heat wave was associated with the development of an extraordinarily strong and prolonged extratropical atmospheric blocking event in association with the excitation of a large-scale atmospheric Rossby wave train spanning western Russia, Kazakhstan, and the northwestern China–Tibetan Plateau region. The southward penetration of upper-level vorticity perturbations in the leading trough of the Rossby wave was instrumental in triggering anomalously heavy rain events over northern Pakistan and vicinity in mid- to late July. Also shown are evidences that the Russian heat wave was amplified by a positive feedback through changes in surface energy fluxes between the atmospheric blocking pattern and an underlying extensive land region with below-normal soil moisture. The Pakistan heavy rain events were amplified and sustained by strong anomalous southeasterly flow along the Himalayan foothills and abundant moisture transport from the Bay of Bengal in connection with the northward propagation of the monsoonal intraseasonal oscillation.

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Aerial Rivers and Lakes: Looking at Large-Scale Moisture Transport and Its Relation to Amazonia and to Subtropical Rainfall in South America

Journal of Climate ◽

10.1175/2011jcli4189.1 ◽

2012 ◽

Vol 25 (2) ◽

pp. 543-556 ◽

Cited By ~ 70

Author(s):

Josefina Moraes Arraut ◽

Carlos Nobre ◽

Henrique M. J. Barbosa ◽

Guillermo Obregon ◽

José Marengo

Keyword(s):

South America ◽

Moisture Transport ◽

Large Scale ◽

Precipitable Water ◽

Trade Wind ◽

Strong Increase ◽

The North ◽

The Andes ◽

Dry Seasons ◽

Southern Amazonia

Abstract This is an observational study of the large-scale moisture transport over South America, with some analyses on its relation to subtropical rainfall. The concept of aerial rivers is proposed as a framework: it is an analogy between the main pathways of moisture flow in the atmosphere and surface rivers. Opposite to surface rivers, aerial rivers gain (lose) water through evaporation (precipitation). The magnitude of the vertically integrated moisture transport is discharge, and precipitable water is like the mass of the liquid column—multiplied by an equivalent speed it gives discharge. Trade wind flow into Amazonia, and the north/northwesterly flow to the subtropics, east of the Andes, are aerial rivers. Aerial lakes are the sections of a moisture pathway where the flow slows down and broadens, because of diffluence, and becomes deeper, with higher precipitable water. This is the case over Amazonia, downstream of the trade wind confluence. In the dry season, moisture from the aerial lake is transported northeastward, but weaker flow over southern Amazonia heads southward toward the subtropics. Southern Amazonia appears as a source of moisture to this flow. Aerial river discharge to the subtropics is comparable to that of the Amazon River. The variations of the amount of moisture coming from Amazonia have an important effect over the variability of discharge. Correlations between the flow from Amazonia and subtropical rainfall are not strong. However, some months within the set of dry seasons observed showed a strong increase (decrease) occurring together with an important increase (decrease) in subtropical rainfall.

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Dynamical Evolution of North Atlantic Ridges and Poleward Jet Stream Displacements

Journal of the Atmospheric Sciences ◽

10.1175/2011jas3661.1 ◽

2011 ◽

Vol 68 (5) ◽

pp. 954-963 ◽

Cited By ~ 33

Author(s):

Tim Woollings ◽

Joaquim G. Pinto ◽

João A. Santos

Keyword(s):

Rossby Wave ◽

North Atlantic ◽

Wave Breaking ◽

Large Scale ◽

Wave Train ◽

Jet Stream ◽

Rossby Wave Breaking ◽

The North ◽

The North Atlantic ◽

Circulation Anomalies

Abstract The development of a particular wintertime atmospheric circulation regime over the North Atlantic, comprising a northward shift of the North Atlantic eddy-driven jet stream and an associated strong and persistent ridge in the subtropics, is investigated. Several different methods of analysis are combined to describe the temporal evolution of the events and relate it to shifts in the phase of the North Atlantic Oscillation and East Atlantic pattern. First, the authors identify a close relationship between northward shifts of the eddy-driven jet, the establishment and maintenance of strong and persistent ridges in the subtropics, and the occurrence of upper-tropospheric anticyclonic Rossby wave breaking over Iberia. Clear tropospheric precursors are evident prior to the development of the regime, suggesting a preconditioning of the Atlantic jet stream and an upstream influence via a large-scale Rossby wave train from the North Pacific. Transient (2–6 days) eddy forcing plays a dual role, contributing to both the initiation and then the maintenance of the circulation anomalies. During the regime there is enhanced occurrence of anticyclonic Rossby wave breaking, which may be described as low-latitude blocking-like events over the southeastern North Atlantic. A strong ridge is already established at the time of wave-breaking onset, suggesting that the role of wave-breaking events is to amplify the circulation anomalies rather than to initiate them. Wave breaking also seems to enhance the persistence, since it is unlikely that a persistent ridge event occurs without being also accompanied by wave breaking.

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Cyclogenesis Simulation of Typhoon Prapiroon (2000) Associated with Rossby Wave Energy Dispersion*

Monthly Weather Review ◽

10.1175/2009mwr3005.1 ◽

2010 ◽

Vol 138 (1) ◽

pp. 42-54 ◽

Cited By ~ 7

Author(s):

Xuyang Ge ◽

Tim Li ◽

Melinda S. Peng

Keyword(s):

Rossby Wave ◽

Wave Energy ◽

Large Scale ◽

Wave Train ◽

Energy Dispersion ◽

Sensitivity Experiment ◽

Low Level ◽

Filtering Technique ◽

Upper Level

Abstract The genesis of Typhoon Prapiroon (2000), in the western North Pacific, is simulated to understand the role of Rossby wave energy dispersion of a preexisting tropical cyclone (TC) in the subsequent genesis event. Two experiments are conducted. In the control experiment (CTL), the authors retain both the previous typhoon, Typhoon Bilis, and its wave train in the initial condition. In the sensitivity experiment (EXP), the circulation of Typhoon Bilis was removed based on a spatial filtering technique of Kurihara et al., while the wave train in the wake is kept. The comparison between these two numerical simulations demonstrates that the preexisting TC impacts the subsequent TC genesis through both a direct and an indirect process. The direct process is through the conventional barotropic Rossby wave energy dispersion, which enhances the low-level wave train, the boundary layer convergence, and the convection–circulation feedback. The indirect process is through the upper-level outflow jet. The asymmetric outflow jet induces a secondary circulation with a strong divergence tendency to the left-exit side of the outflow jet. The upper-level divergence boosts large-scale ascending motion and promotes favorable environmental conditions for a TC-scale vortex development. In addition, the outflow jet induces a well-organized cyclonic eddy angular momentum flux, which acts as a momentum forcing that enhances the upper-level outflow and low-level inflow and favors the growth of the new TC.

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Dynamics of Landfalling Atmospheric Rivers over the North Pacific in 30 Years of MERRA Reanalysis

Journal of Climate ◽

10.1175/jcli-d-14-00034.1 ◽

2014 ◽

Vol 27 (18) ◽

pp. 7133-7150 ◽

Cited By ~ 75

Author(s):

Ashley E. Payne ◽

Gudrun Magnusdottir

Keyword(s):

Rossby Wave ◽

West Coast ◽

Wave Breaking ◽

Moisture Transport ◽

Large Scale ◽

Eastern Pacific ◽

The West ◽

Atmospheric Rivers ◽

Rossby Wave Breaking ◽

Upper Level

Abstract A large-scale analysis of landfalling atmospheric rivers (ARs) along the west coast of North America and their association with the upper-tropospheric flow is performed for the extended winter (November–March) for the years 1979–2011 using Modern-Era Retrospective Analysis for Research and Applications (MERRA) reanalysis data. The climatology, relationship to the El Niño–Southern Oscillation and the Madden–Julian oscillation, and upper-level characteristics of approximately 750 landfalling ARs are presented based on the 85th percentile of peak daily moisture flux. AR occurrence along the West Coast is dominated by early season events. In composites of upper-level fields during AR occurrences, certain characteristics stand out irrespective of the tropical climate indices. This suggests that extratropical dynamical processes play a key role in AR dynamics. The influence of the large-scale circulation on AR intensity prior to landfall is examined by objectively selecting an extreme subset of 112 landfalling AR dates representing the 95th percentile of strongest cases. Each landfalling AR date that is identified is traced backward in time using a novel semiautomated tracking algorithm based on spatially and temporally connected organized features in integrated moisture transport. Composites of dynamical fields following the eastward progression of ARs show a close relationship of the location of the jet, Rossby wave propagation, and anticyclonic Rossby wave breaking in the upper troposphere of the eastern Pacific and moisture transport in the lower troposphere. Comparison between the strongest and the weakest ARs within the most extreme subset shows differences in both the intensity of moisture transport and the scale and development of anticyclonic Rossby wave breaking in the eastern Pacific.

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Probing Regional Orographic Controls of Precipitation and Cloudiness in the Central Andes Using Satellite Data

Journal of Hydrometeorology ◽

10.1175/2008jhm973.1 ◽

2009 ◽

Vol 10 (1) ◽

pp. 167-182 ◽

Cited By ~ 52

Author(s):

Jason P. Giovannettone ◽

Ana P. Barros

Keyword(s):

Moisture Transport ◽

Large Scale ◽

Tropical Rainfall Measuring Mission ◽

Space Time ◽

Cloud Formation ◽

Time Variability ◽

Brightness Temperatures ◽

The Andes ◽

Precipitation Regimes ◽

One Year

Abstract Data obtained from NOAA’s Geostationary Operational Environmental Satellite (GOES) and NASA’s Tropical Rainfall Measuring Mission (TRMM) satellites were used to investigate the relationships between topography, large-scale circulation, and the climatology of precipitation and cloudiness in the Andes—specifically over Peru and the Altiplano Plateau—at diurnal, seasonal, and interannual time scales. The spatial variability of cloudiness was assessed through empirical orthogonal function (EOF) analysis of GOES brightness temperatures. Results indicate that landform is the principal agent of the space–time variability of moist atmospheric processes in the Andes, with the first mode explaining up to 70% of all observed variability. These results substantiate the differences between “continental” (Andes and Himalayas) and “maritime” (Western Cordillera) orographic precipitation regimes, reflecting the degree to which upwind landmasses modulate moisture transport toward and across mountain barriers. GOES brightness temperatures show that afternoon convective activity during the rainy season is more intense on wet hydrometeorological years such as 2001, whereas the space–time structure of nighttime cloudiness at the foothills and outlets of deep interior valleys does not change during the monsoon and from one year to another independently of large-scale conditions. This suggests that daytime cloud formation and precipitation is strongly dependent on large-scale moisture transport. Interactions between mesoscale and ridge–valley circulations, which are locked to the topography, determine the space–time organization of clouds and precipitation at nighttime. This leads to strong clustering of precipitation features associated with enhanced convection at high elevations along the ridges and near the headwaters of the major river systems in the TRMM data.

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Rossby wave activity associated with Euro-Atlantic weather regimes in the PRIMAVERA historical runs.

10.5194/egusphere-egu21-9605 ◽

2021 ◽

Author(s):

Paolo Ghinassi ◽

Federico Fabiano ◽

Susanna Corti

Keyword(s):

Spatial Distribution ◽

High Resolution ◽

Rossby Wave ◽

Large Scale ◽

Wave Activity ◽

Large Scale Circulation ◽

Temporal Behaviour ◽

Weather Regime ◽

Weather Regimes ◽

Isentropic Coordinates

In this study we aim to assess how the upper tropospheric Rossby wave activity is represented in the PRIMAVERA models. The low and high resolution historical coupled simulations will be compared with ERA5 reanalysis (spanning the 1979-2014 period) to enlighten model deficiencies in representing the spatial distribution and temporal evolution of Rossby wave activity and to emphasize the benefits of increased resolution. Our analysis focuses on the wintertime large scale circulation over the Euro-Atlantic sector. A diagnostic based on Local Wave Activity (LWA) in isentropic coordinates is used to identify Rossby waves and to quantify their amplitude. LWA is partitioned into its stationary and transient components, to distinguish the contribution from planetary versus synoptic scale waves (i.e. wave packets). This diagnostic is then combined with another one to identify persistent and recurrent large scale circulation patterns, the so called weather regimes. Weather regimes in the Euro-Atlantic sector are identified with the usual approach of EOF decomposition and k-mean clustering applied to daily anomalies of Montgomery streamfunction, in order to have a consistent framework with LWA (which is defined in isentropic coordinates). A composite of transient LWA is realised for each weather regime to obtain the spatial distribution of Rossby wave activity associated with each weather regime.Results show a marked intermodel variability in the ability of reproducing the correct (i.e. the one observed in reanalysis data) LWA distribution. Many of the models in fact fails to reproduce the localized (in space) maxima of LWA associated with each weather regime and to distribute LWA over a larger region compared to reanalysis. High resolution helps to correct this bias in the majority of the models, in particular in those where the low-resolution LWA distribution was already close to reanalysis. Finally, the temporal behaviour of the spatially averaged LWA in the examined period is discussed.

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High Resolution WRF Regional Climate Modeling for the Andes-Amazon Transition Region: Model Validation Early Results

10.5194/egusphere-egu2020-11687 ◽

2020 ◽

Author(s):

Juan Pablo Sierra ◽

Clementine Junquas ◽

Jhan Carlo Epinoza ◽

Thierry Lebel ◽

Hans Segura

Keyword(s):

High Resolution ◽

Transition Region ◽

Land Surface ◽

Large Scale ◽

Amazon Basin ◽

Climate Model ◽

Rainfall Variability ◽

Regional Climate ◽

The Andes ◽

Early Results

The western Amazon and eastern flank of the Andes form what is known as the Amazon-Andes transition region. This region is characterized by the presence of the rainiest area in the Amazon basin with an average precipitation ranging from 6000 to 7000 mm per year. This rainy zone is the result of interactions between large-scale circulation and local features. However, the physical mechanisms controlling this rainfall patterns in the transition region are poorly understood. On the other hand, high precipitation values in the area, along with erosion, sediment transport and the geological mountain uplift help to explain this region as one of the most species-rich terrestrial ecosystems. Nevertheless, accelerated deforestation rates reported both in tropical Andes and central-southern Amazon threat the biodiversity hotspots and can induce alterations in land surface energy and water balances. In this context, the use of regional climate models can shed light on the possible consequences of deforestation on rainfall in the transition region. The early results presented here are the first step in a work that seeks to gain a better understanding in the mechanisms involved in precipitation generation over the Amazon-Andes transition region, as well as the assessment of deforestation impacts on spatial and temporal rainfall variability during austral summer. The Weather Research and Forecasting (WRF) regional climate model is used with three nested domains. High resolution simulations (1km horizontal grid size) are performed over the key regions of Cuzco and Bolivian slopes. As a perspective,&#160; deforestation scenarios following the land use change trajectory observed during the last decade will be used in future works. The results of this work can help to dimension the consequences of deforestation on key ecosystems such as Andean hotspots.

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