Atmospheric dynamics of extreme discharge events from 1979 to 2016 in the southern Central Andes

Abstract During the South-American Monsoon season, deep convective systems occur at the eastern flank of the Central Andes leading to heavy rainfall and flooding. We investigate the large- and meso-scale atmospheric dynamics associated with extreme discharge events (> 99.9th percentile) observed in two major river catchments meridionally stretching from humid to semi-arid conditions in the southern Central Andes. Based on daily gauge time series and ERA-Interim reanalysis, we made the following three key observations: (1) for the period 1940–2016 daily discharge exhibits more pronounced variability in the southern, semi-arid than in the northern, humid catchments. This is due to a smaller ratio of discharge magnitudes between intermediate (0.2 year return period) and rare events (20 year return period) in the semi-arid compared to the humid areas; (2) The climatological composites of the 40 largest discharge events showed characteristic atmospheric features of cold surges based on 5-day time-lagged sequences of geopotential height at different levels in the troposphere; (3) A subjective classification revealed that 80% of the 40 largest discharge events are mainly associated with the north-northeastward migration of frontal systems and 2/3 of these are cold fronts, i.e. cold surges. This work highlights the importance of cold surges and their related atmospheric processes for the generation of heavy rainfall events and floods in the southern Central Andes.

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Timing and extent of late pleistocene glaciation in the arid Central Andes of Argentina and Chile (22°-41°S)

Cuadernos de Investigación Geográfica ◽

10.18172/cig.3235 ◽

2017 ◽

Vol 43 (2) ◽

pp. 697 ◽

Cited By ~ 7

Author(s):

J. Zech ◽

C. Terrizzano ◽

E. García-Morabito ◽

H. Veit ◽

R. Zech

Keyword(s):

Southern Oscillation ◽

Co2 Concentration ◽

Late Glacial ◽

Central Andes ◽

The North ◽

Eastern Equatorial Pacific ◽

Southern Central ◽

Study Sites ◽

Increasing Temperature ◽

Exposure Ages

The arid Central Andes are a key site to study changes in intensity and movement of the three main atmospheric circulation systems over South America: the South American Summer Monsoon (SASM), the Westerlies and the El Niño Southern Oscillation (ENSO). In this semi-arid to arid region glaciers are particularly sensitive to precipitation changes and thus the timing of past glaciation is strongly linked to changes in moisture supply. Surface exposure ages from study sites between 41° and 22°S suggest that glaciers advanced: i) prior to the global Last Glacial Maximum (gLGM) at ~40 ka in the mid (26°- 30°S) and southern Central Andes (35°-41°S), ii) in phase with the gLGM in the northern and southern Central Andes and iii) during the late glacial in the northern Central Andes. Deglaciation started synchronous with the global rise in atmospheric CO2 concentration and increasing temperature starting at ~18 ka. The pre-gLGM glacial advances likely document enhanced precipitation related to the Southern Westerlies, which shifted further to the North at that time than previosuly assumed. During the gLGM glacial advances were favored by decreased temperatures in combination with increased humidity due to a southward shifted Intertropical Convergence Zone (ITCZ) and SASM. During the late-glacial a substantial increase in moisture can be explained by enhanced upper tropospheric easterlies as response to an intensified SASM and sustained La Niña-like conditions over the eastern equatorial Pacific that lead to glacial advances in the northern Central Andes and the lake level highstand Tauca (18-14 ka) on the Altiplano. In the southernmost Central Andes at 39º-41°S, further north at 31°S and in the northernmost Central Andes at 22°S glacial remnants even point to precipitation driven glaciations older than ~115 ka and 260 ka.

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Tertiary tectonics of the sub-Andean region of the North Patagonian Andes, southern central Andes of Argentina (41–42°30′S)

Journal of South American Earth Sciences ◽

10.1016/j.jsames.2005.05.013 ◽

2005 ◽

Vol 20 (3) ◽

pp. 157-170 ◽

Cited By ~ 40

Author(s):

Raúl E. Giacosa ◽

Juan C. Afonso ◽

Nemesio Heredia C. ◽

José Paredes

Keyword(s):

Central Andes ◽

Andean Region ◽

The North ◽

Southern Central ◽

Patagonian Andes

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Analysis of rainfall trends over Tripura

MAUSAM ◽

10.54302/mausam.v73i1.5078 ◽

2022 ◽

Vol 73 (1) ◽

pp. 27-36

Author(s):

RANJAN PHUKAN ◽

D. SAHA

Keyword(s):

Heavy Rainfall ◽

Monsoon Season ◽

Rainfall Variability ◽

Kendall Test ◽

Annual Rainfall ◽

The North ◽

Rainfall Trends ◽

Annual Scale ◽

Increasing Trends ◽

Rainy Days

Rainfall in India has very high temporal and spatial variability. The rainfall variability affects the livelihood and food habits of people from different regions. In this study, the rainfall trends in two stations in the north-eastern state of Tripura, namely Agartala and Kailashahar have been studied for the period 1955-2017. The state experiences an annual mean of more than 2000 mm of rainfall, out of which, about 60% occurs during the monsoon season and about 30% in pre-monsoon. An attempt has been made to analyze the trends in seasonal and annual rainfall, rainy days and heavy rainfall in the two stations, during the same period.Non-parametric Mann-Kendall test has been used to find out the significance of these trends. Both increasing and decreasing trends are observed over the two stations. Increasing trends in rainfall, rainy days and heavy rainfall are found at Agartala during pre-monsoon season and decreasing trends in all other seasons and at annual scale. At Kailashahar, rainfall amount (rainy days & heavy rainfall) is found to be increasing during pre-monsoon and monsoon seasons (pre-monsoon season). At annual scale also, rainfall and rainy days show increasing trends at Kailashahar. The parameters are showing decreasing trends during all other seasons at the station. Rainy days over Agartala show a significantly decreasing trend in monsoon, whereas no other trend is found to be significant over both the stations.

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Evaluating Forecast Skills of Moisture from Convective-Permitting WRF-ARW Model during 2017 North American Monsoon Season

Atmosphere ◽

10.3390/atmos10110694 ◽

2019 ◽

Vol 10 (11) ◽

pp. 694 ◽

Cited By ~ 1

Author(s):

Christoforus Bayu Risanto ◽

Christopher L. Castro ◽

James M. Moker ◽

Avelino F. Arellano ◽

David K. Adams ◽

...

Keyword(s):

North American ◽

Monsoon Season ◽

Precipitable Water ◽

Weather Forecast ◽

Moisture Flux ◽

Rain Gauge ◽

North American Monsoon ◽

Convective Systems ◽

The North ◽

Northwestern Mexico

This paper examines the ability of the Weather Research and Forecasting model forecast to simulate moisture and precipitation during the North American Monsoon GPS Hydrometeorological Network field campaign that took place in 2017. A convective-permitting model configuration performs daily weather forecast simulations for northwestern Mexico and southwestern United States. Model precipitable water vapor (PWV) exhibits wet biases greater than 0.5 mm at the initial forecast hour, and its diurnal cycle is out of phase with time, compared to observations. As a result, the model initiates and terminates precipitation earlier than the satellite and rain gauge measurements, underestimates the westward propagation of the convective systems, and exhibits relatively low forecast skills on the days where strong synoptic-scale forcing features are absent. Sensitivity analysis shows that model PWV in the domain is sensitive to changes in initial PWV at coastal sites, whereas the model precipitation and moisture flux convergence (QCONV) are sensitive to changes in initial PWV at the mountainous sites. Improving the initial physical states, such as PWV, potentially increases the forecast skills.

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Characteristics of Deep Cloud Systems under Weak and Strong Synoptic Forcing during the Indian Summer Monsoon Season

Monthly Weather Review ◽

10.1175/mwr-d-18-0346.1 ◽

2019 ◽

Vol 147 (10) ◽

pp. 3741-3758 ◽

Cited By ~ 2

Author(s):

Jayesh Phadtare ◽

G. S. Bhat

Keyword(s):

Monsoon Season ◽

Propagation Speed ◽

Maximum Size ◽

Gradient Field ◽

Synoptic Scale ◽

Pressure System ◽

Cloud Systems ◽

Convective Systems ◽

The North ◽

Synoptic Forcing

Abstract Synoptic-scale weather systems are often responsible for initiating mesoscale convective systems (MCSs). Here, we explore how synoptic forcing influences MCS characteristics, such as the maximum size, lifespan, cloud-top height, propagation speed, and triggering over the Indian region. We used 30-min interval infrared (IR) data of the Indian Kalpana-1 geostationary satellite. Cloud systems (CSs) in this data are identified and tracked using an object tracking algorithm. ERA-Interim 850-hPa vorticity is taken as a proxy for the synoptic forcing. The probability of CSs being larger, longer lived, and deeper is more in the presence of a synoptic-scale vorticity field; however, the influence of synoptic forcing is not evident on the westward propagation of CSs over land. There exists a linear relationship between maximum size, lifespan, and average cloud-top height of CSs regardless of the nature of synoptic forcing. Formation of CSs peaks around 1500 LST over land, which is independent of synoptic forcing. Over the north Bay of Bengal, CSs formation is predominantly nocturnal when synoptic forcing is strong, whereas, 0300 and 1200 LST are the preferred times when synoptic forcing is weak. Long-lived CSs are preferentially triggered in the western flank of the 850-hPa vorticity gradient field of a monsoon low pressure system. Once triggered, CSs propagate westward and ahead of the synoptic system and dissipate around midnight. Formation of new CSs on the next day occurs in the afternoon hours in the wake of previous day’s CSs and where vorticity gradient is also present. Formation and westward propagations of CSs on successive days move the synoptic envelope westward.

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