scholarly journals Detection of Spatial Rainfall Variation over the Andean Region Demonstrated by Satellite-Based Observations

Atmosphere ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1204
Author(s):  
Dibas Shrestha ◽  
Shankar Sharma ◽  
Rocky Talchabhadel ◽  
Rashila Deshar ◽  
Kalpana Hamal ◽  
...  
Keyword(s):  
Global Climate ◽  
Deep Convection ◽  
Austral Summer ◽  
Tropical Rainfall Measuring Mission ◽  
Andean Region ◽  
Southern Andes ◽  
Low Level ◽  
Rainfall Variation ◽  
The Andes ◽  
Study Characteristics

Topography has an important role in shaping regional and global climate systems, as it acts as a mechanical barrier to the low-level moisture flow. Thus, a complex spatial pattern of rainfall can exist over the mountainous region. Moreover, it is critical to advance our understanding of the relationship between rainfall and topography in terms of rainfall timing, frequency, and magnitude. In this study, characteristics of austral summer (December–February) precipitation are analyzed using 17-year (1998–2014) high-spatial-resolution (0.05° × 0.05°) data obtained from the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) over the Andean region focusing on topographic impact. We observe an interaction between precipitation patterns and topography, with clear precipitation–elevation relationships in the Andes regions. The rainfall maxima zone was observed over the higher terrain of the central and southern Andes, and the zone is attributed to frequency and intensity of rainfall, respectively. In the foothills of the central Andes, we find there was a persistent rain system when a moist, low-level flow was lifted due to topography. In contrast, steep mountain slopes and a relatively dry atmosphere modulate deep convection in the foothills of southern Andes.

scholarly journals Hydrological differentiation and spatial distribution of high altitude wetlands in a semi-arid Andean region derived from satellite data

2011 ◽  
Vol 8 (1) ◽  
pp. 1287-1327 ◽  
Author(s):  
M. Otto ◽  
D. Scherer ◽  
J. Richters
Keyword(s):  
High Altitude ◽  
Satellite Data ◽  
Regional Scale ◽  
Austral Summer ◽  
Monthly Precipitation ◽  
Austral Winter ◽  
Andean Region ◽  
Study Region ◽  
The Andes ◽  
Semi Arid

Abstract. High Altitude Wetlands of the Andes (HAWA) are unique types of wetlands within the semi-arid high Andean region. Knowledge about HAWA has been derived mainly from studies at single sites within different parts of the Andes at only small time scales. On the one hand HAWA depend on water provided by glacier streams, snow melt or precipitation. On the other hand, they are suspected to influence hydrology through water retention and vegetation growth altering stream flow velocity. We derived HAWA land cover from satellite data at regional scale and analysed changes in connection with precipitation over the last decade. Perennial and temporal HAWA subtypes can be distinguished by seasonal changes of photosynthetically active vegetation (PAV) indicating the perennial or temporal availability of water during the year. HAWA have been delineated within a region of 11 000 km2 situated in the Northwest of Lake Titicaca. The multi temporal classification method used Normalized Differenced Vegetation Index (NDVI) and Normalized Differenced Infrared Index (NDII) data derived from two Landsat ETM+ scenes at the end of austral winter (September 2000) and at the end of austral summer (May 2001). The mapping result indicates an unexpected high abundance of HAWA covering about 800 km2 of the study region (6%). Annual HAWA mapping was computed using NDVI 16-day composites of Moderate Resolution Imaging Spectroradiometer (MODIS). Analyses on the reletation between HAWA and precipitation was based on monthly precipitation data of the Tropical Rain Measurement Mission (TRMM 3B43) and MODIS Eight Day Maximum Snow Extent data (MOD10A2) from 2000 to 2010. We found HAWA subtype specific dependencies to precipitation conditions. Strong relation exists between perennial HAWA and snow fall (r2: 0.82) in dry austral winter months (June to August) and between temporal HAWA and precipitation (r2: 0.75) during austral summer (March to May). Annual spatial patterns of perennial HAWA indicated spatial alteration of water supply for PAV up to several hundred metres at a single HAWA site.

scholarly journals Numerical simulation of a rare winter hailstorm event over Delhi, India on 17 January 2013

2014 ◽  
Vol 14 (12) ◽  
pp. 3331-3344 ◽  
Author(s):  
A. Chevuturi ◽  
A. P. Dimri ◽  
U. B. Gunturu
Keyword(s):  
Numerical Simulation ◽  
Deep Convection ◽  
Baroclinic Instability ◽  
Wrf Model ◽  
Tropical Rainfall Measuring Mission ◽  
Cloud Formation ◽  
New Delhi ◽  
National Capital Region ◽  
Microphysics Scheme ◽  
Low Level

Abstract. This study analyzes the cause of the rare occurrence of a winter hailstorm over New Delhi/NCR (National Capital Region), India. The absence of increased surface temperature or low level of moisture incursion during winter cannot generate the deep convection required for sustaining a hailstorm. Consequently, NCR shows very few cases of hailstorms in the months of December-January-February, making the winter hail formation a question of interest. For this study, a recent winter hailstorm event on 17 January 2013 (16:00–18:00 UTC) occurring over NCR is investigated. The storm is simulated using the Weather Research and Forecasting (WRF) model with the Goddard Cumulus Ensemble (GCE) microphysics scheme with two different options: hail and graupel. The aim of the study is to understand and describe the cause of hailstorm event during over NCR with a comparative analysis of the two options of GCE microphysics. Upon evaluating the model simulations, it is observed that the hail option shows a more similar precipitation intensity with the Tropical Rainfall Measuring Mission (TRMM) observation than the graupel option does, and it is able to simulate hail precipitation. Using the model-simulated output with the hail option; detailed investigation on understanding the dynamics of hailstorm is performed. The analysis based on a numerical simulation suggests that the deep instability in the atmospheric column led to the formation of hailstones as the cloud formation reached up to the glaciated zone promoting ice nucleation. In winters, such instability conditions rarely form due to low level available potential energy and moisture incursion along with upper level baroclinic instability due to the presence of a western disturbance (WD). Such rare positioning is found to be lowering the tropopause with increased temperature gradient, leading to winter hailstorm formation.

scholarly journals Hydrological differentiation and spatial distribution of high altitude wetlands in a semi-arid Andean region derived from satellite data

2011 ◽  
Vol 15 (5) ◽  
pp. 1713-1727 ◽  
Author(s):  
M. Otto ◽  
D. Scherer ◽  
J. Richters
Keyword(s):  
High Altitude ◽  
Satellite Data ◽  
Austral Summer ◽  
Snow Melt ◽  
Austral Winter ◽  
Andean Region ◽  
Unique Type ◽  
Study Region ◽  
The Andes ◽  
Semi Arid

Abstract. High Altitude Wetlands of the Andes (HAWA) belong to a unique type of wetland within the semi-arid high Andean region. Knowledge about HAWA has been derived mainly from studies at single sites within different parts of the Andes at only small time scales. On the one hand, HAWA depend on water provided by glacier streams, snow melt or precipitation. On the other hand, they are suspected to influence hydrology through water retention and vegetation growth altering stream flow velocity. We derived HAWA land cover from satellite data at regional scale and analysed changes in connection with precipitation over the last decade. Perennial and temporal HAWA subtypes can be distinguished by seasonal changes of photosynthetically active vegetation (PAV) indicating the perennial or temporal availability of water during the year. HAWA have been delineated within a region of 12 800 km2 situated in the Northwest of Lake Titicaca. The multi-temporal classification method used Normalized Differenced Vegetation Index (NDVI) and Normalized Differenced Infrared Index (NDII) data derived from two Landsat ETM+ scenes at the end of austral winter (September 2000) and at the end of austral summer (May 2001). The mapping result indicates an unexpected high abundance of HAWA covering about 800 km2 of the study region (6 %). Annual HAWA mapping was computed using NDVI 16-day composites of Moderate Resolution Imaging Spectroradiometer (MODIS). Analyses on the relation between HAWA and precipitation was based on monthly precipitation data of the Tropical Rain Measurement Mission (TRMM 3B43) and MODIS Eight Day Maximum Snow Extent data (MOD10A2) from 2000 to 2010. We found HAWA subtype specific dependencies on precipitation conditions. A strong relation exists between perennial HAWA and snow fall (r2: 0.82) in dry austral winter months (June to August) and between temporal HAWA and precipitation (r2: 0.75) during austral summer (March to May). Annual changes in spatial extend of perennial HAWA indicate alterations in annual water supply generated from snow melt.

scholarly journals Inter-El Niño variability and its impact on the South American low-level jet east of the Andes during austral summer − two case studies

2006 ◽  
Vol 6 ◽  
pp. 283-287 ◽  
Author(s):  
G. A. M. Silva ◽  
T. Ambrizzi
Keyword(s):  
El Niño ◽  
El Nino ◽  
Austral Summer ◽  
South American ◽  
The South ◽  
Trade Winds ◽  
Low Level ◽  
The Andes ◽  
Low Level Jet ◽  
The Impact

Abstract. The impact of the maximum convection location over eastern and central Equatorial Pacific over the intensity and positioning of the South American Low-Level Jet east of the Andes (SALLJ) during the austral summer was investigated. The Bonner criteria 1 was applied to the NCEP-NCAR circulation fields during the El Niño of 1997/1998 and 2002/2003 to identify the SALLJ episodes. The composites of the atmospheric circulation over the South America during El Niño events showed that the SALLJ can be influenced by small displacements of the quasi-stationary Rossby waves position. During the strong El Niño event of 1997/1998 the SALLJ is maintained by the eastern trade winds. A low-level anomalous anticyclonic circulation over the central part of Brazil enhanced the wind in the nucleus of the jet and displaced its axis to the Northern Argentina and South of Brazil. However, the northern trade winds seem to maintain the SALLJ during the weak El Niño of 2002/2003. The jet was weaker and displaced more southeastward of Brazil than during the strong event.

scholarly journals Diurnal variability of rainfall in southwest Amazonia during the LBA-TRMM field campaign of the austral summer of 1999

2004 ◽  
Vol 34 (4) ◽  
pp. 593-603 ◽  
Author(s):  
José A. Marengo ◽  
Gilberto Fisch ◽  
Carlos Morales ◽  
Iria Vendrame ◽  
Paulo C. Dias
Keyword(s):  
Large Scale ◽  
Surface Wind ◽  
Austral Summer ◽  
Early Morning ◽  
South Atlantic Convergence Zone ◽  
Diurnal Variability ◽  
Field Campaign ◽  
Low Level ◽  
The Andes ◽  
Local Standard

The TRMM-LBA field campaign was held during the austral summer of 1999 in southwestern Amazonia. Among the major objectives, was the identification and description of the diurnal variability of rainfall in the region, associated with the different rain producing weather systems that occurred during the January-February season. By using a network of 40 digital rain gauges implemented in the state of Rondônia, and together with observations and analyses of circulation and convection, it was possible to identify details of the diurnal cycle of rainfall and the associated rainfall mechanisms. Rainfall episodes were characterized by regimes of "low-level easterly" and "westerly" winds in the context of the large-scale circulation. The westerly regime is related to an enhanced South Atlantic Convergence Zone (SACZ) and an intense and/or wide Low Level Jet (LLJ) east of the Andes, which can extend eastward towards Rondônia, even though some westerly regime episodes also show a LLJ that remains close to the foothill of the Andes. The easterly regime is related to easterly propagating systems (e.g. squall-lines) with possible weakened or less frequent LLJs and a suppressed SACZ. Diurnal variability of rainfall during westerly surface wind regime shows a characteristic maximum at late afternoon followed by a relatively weaker second maximum at early evening (2100 Local Standard Time LST). The easterly regime composite shows an early morning maximum followed by an even stronger maximum in the afternoon.

scholarly journals Improving Simulations of Convective Systems from TRMM LBA: Easterly and Westerly Regimes

2007 ◽  
Vol 64 (4) ◽  
pp. 1141-1164 ◽  
Author(s):  
S. Lang ◽  
W-K. Tao ◽  
J. Simpson ◽  
R. Cifelli ◽  
S. Rutledge ◽  
...  
Keyword(s):  
Large Scale ◽  
Collection Efficiency ◽  
Deep Convection ◽  
Tropical Rainfall Measuring Mission ◽  
Squall Line ◽  
Gradual Transition ◽  
Microphysics Scheme ◽  
Easterly Wind ◽  
Low Level ◽  
Convective Systems

Abstract The 3D Goddard Cumulus Ensemble model is used to simulate two convective events observed during the Tropical Rainfall Measuring Mission Large-Scale Biosphere–Atmosphere (TRMM LBA) experiment in Brazil. These two events epitomized the type of convective systems that formed in two distinctly different environments observed during TRMM LBA. The 26 January 1999 squall line formed within a sheared low-level easterly wind flow. On 23 February 1999, convection developed in weak low-level westerly flow, resulting in weakly organized, less intense convection. Initial simulations captured the basic organization and intensity of each event. However, improvements to the model resolution and microphysics produced better simulations as compared to observations. More realistic diurnal convective growth was achieved by lowering the horizontal grid spacing from 1000 to 250 m. This produced a gradual transition from shallow to deep convection that occurred over a span of hours as opposed to an abrupt appearance of deep convection. Eliminating the dry growth of graupel in the bulk microphysics scheme effectively removed the unrealistic presence of high-density ice in the simulated anvil. However, comparisons with radar reflectivity data using contoured-frequency-with-altitude diagrams (CFADs) revealed that the resulting snow contents were too large. The excessive snow was reduced primarily by lowering the collection efficiency of cloud water by snow and resulted in further agreement with the radar observations. The transfer of cloud-sized particles to precipitation-sized ice appears to be too efficient in the original scheme. Overall, these changes to the microphysics lead to more realistic precipitation ice contents in the model. However, artifacts due to the inability of the one-moment scheme to allow for size sorting, such as excessive low-level rain evaporation, were also found but could not be resolved without moving to a two-moment or bin scheme. As a result, model rainfall histograms underestimated the occurrence of high rain rates compared to radar-based histograms. Nevertheless, the improved precipitation-sized ice signature in the model simulations should lead to better latent heating retrievals as a result of both better convective–stratiform separation within the model as well as more physically realistic hydrometeor structures for radiance calculations.

The Influence of the Andes on Cutoff Lows: A Modeling Study*

2007 ◽  
Vol 135 (4) ◽  
pp. 1596-1613 ◽  
Author(s):  
RenéD. Garreaud ◽  
Humberto A. Fuenzalida
Keyword(s):  
Latent Heat ◽  
Deep Convection ◽  
Wrf Model ◽  
Austral Summer ◽  
Lower Troposphere ◽  
Dimensional Structure ◽  
Western Slope ◽  
Pressure System ◽  
The Andes ◽  
Andes Cordillera

Abstract A cutoff low (COL) pressure system that occurred in March 2005 (late austral summer) over the subtropical southeast Pacific is examined by means of numerical simulations using the Weather and Research Forecasting (WRF) model. The episode exhibited typical features of COLs in this region, including its formation from an elongated northwest–southeast extratropical trough and subsequent intensification off the west coast of South America. During the developing stage, the cyclonic circulation did not extend into the lower troposphere and only upper-level, nonprecipitating clouds were observed at and around the system. When the COL reached the continent it produced moderate but unseasonal rainfall along the semiarid western slope of the Andes cordillera [summit level at ∼5000 m above sea level (ASL)] at the same time that the system experienced a rapid decay. The control simulation used full physics, full topography, and a single domain (54-km grid spacing) laterally forced by atmospheric reanalysis. Model results are in general agreement with upper-air, surface, and satellite observations, and allow a detailed description of the three-dimensional structure of the COL, as well as an evaluation of the vorticity and temperature budgets. A quasi-stationary, amplifying warm ridge over the South Pacific appears as the key precursor feature, in agreement with studies elsewhere. Once the COL formed, it drifted eastward mostly driven by vorticity advection induced by its own circulation, and there was close balance between vertical and horizontal temperature advection near its center. The jet streak along the COL’s periphery migrated from upstream of the COL axis, during the developing stage, to downstream later on. Four sensitivity experiments—reducing/removing topography, suppressing hydrometeors, and using an enlarged domain—were performed to assess the influence of the Andes, the importance of latent heat release, and the effect of the boundary conditions. Comparison among the control and sensitivity runs indicates that the COL formation occurs regardless of the presence of the Andes, and COL dissipation is mainly due to latent heat released in the deep clouds that form over the mountainous terrain. Nevertheless, the Andes cordillera delayed the COL demise by blocking the inflow of warm, moist air from the interior of the continent that otherwise would initiate deep convection in the region of ascending motion downstream of the COL.

scholarly journals Characteristic Features of Warm-Type Rain Producing Heavy Rainfall over the Korean Peninsula Inferred from TRMM Measurements

2013 ◽  
Vol 141 (11) ◽  
pp. 3873-3888 ◽  
Author(s):  
B. J. Sohn ◽  
Geun-Hyeok Ryu ◽  
Hwan-Jin Song ◽  
Mi-Lim Ou
Keyword(s):  
Water Vapor ◽  
Liquid Water ◽  
Korean Peninsula ◽  
Heavy Rainfall ◽  
Deep Convection ◽  
Tropical Rainfall Measuring Mission ◽  
Heavy Rain ◽  
Low Level ◽  
The North ◽  
Characteristic Features

Abstract In contrast to the view that deep convection causes heavy rainfall, Tropical Rainfall Measuring Mission (TRMM) measurements demonstrate that heavy rainfall (ranging from moderate to extreme rain rate) over the Korean peninsula is associated more with low-level clouds (referred to as warm-type clouds in this study) than with conventional deep convective clouds (cold-type clouds). Moreover, it is noted that the low-level warm-type clouds producing heavy rainfall over Korea appear to be closely linked to the atmospheric river, which can form a channel that transports water vapor across the Korean peninsula along the northwestern periphery of the North Pacific high. Much water vapor is transported through the channel and converges on the Korean peninsula when warm-type heavy rain occurs there. It may be possible to produce abundant liquid water owing to the excess of water vapor; this could increase the rate and extent of raindrop growth, primarily below the melting layer, causing heavy rain when these drops fall to the surface. The occurrence of heavy rainfall (also exhibited as medium-depth convection in radar observations over Okinawa, Japan) due to such liquid-water-rich lower warm clouds should induce difficulties in retrieving rainfall from space owing to the lack of scattering-inducing ice crystals over land and the warmer cloud tops. An understanding of the microphysical processes involved in the production of warm-type rain appears to be a prerequisite for better rain retrieval from space and rain forecasting in this wet region.

Regional and Diurnal Variability of the Vertical Structure of Precipitation Systems in Africa Based on Spaceborne Radar Data

2005 ◽  
Vol 18 (7) ◽  
pp. 893-916 ◽  
Author(s):  
Bart Geerts ◽  
Teferi Dejene
Keyword(s):  
Vertical Structure ◽  
Austral Summer ◽  
Tropical Rainfall Measuring Mission ◽  
Radar Data ◽  
Equatorial Region ◽  
Diurnal Variability ◽  
Low Level ◽  
Freezing Level ◽  
Rainfall Frequency ◽  
The Difference

Abstract The Tropical Rainfall Measuring Mission (TRMM) 2A25 radar reflectivity profiles and derived surface rain rates are used to describe the vertical structure of precipitation systems in Africa. Five years of data are used in both the boreal and austral summer rainy seasons. A number of climate regions are isolated and compared. To place the composite reflectivity profiles in context, they are contrasted against TRMM 2A25 observations over the Amazon. In all of tropical Africa, precipitation systems tend to be deeper and more intense than in the Amazon, and shallow warm-rain events are less common. In all African regions, but especially in the Sahel and northern Savanna, storms are characterized by high echo tops, high hydrometeor loading aloft, little indication of a radar brightband maximum at the freezing level, and evidence for low-level evaporation. Storms in Africa are generally most common, and deepest, in the late afternoon, and weaker shallow systems are relatively more common around noon. The diurnal modulation is regionally variable. The amplitude of the diurnal cycle of the mean echo top height decreases from the arid margins of the zenithal rain region toward the equatorial region, and is smallest in the Amazon. A secondary predawn (0000–0600 LT) maximum occurs in the Congo, in terms of rainfall frequency, rainfall intensity, and echo tops. The storm intensity indicators generally peak a few hours later in the Sahel and northern Savanna than in other regions in Africa. The difference between all African regions and the Amazon, and the relatively smaller differences between regions in Africa, can be understood in terms of the climatological humidity, CAPE, and low-level shear values.

Upstream Orographic Enhancement of a Narrow Cold-Frontal Rainband Approaching the Andes

2013 ◽  
Vol 141 (5) ◽  
pp. 1708-1730 ◽  
Author(s):  
Maximiliano Viale ◽  
Robert A. Houze ◽  
Kristen L. Rasmussen
Keyword(s):  
Wrf Model ◽  
Tropical Rainfall Measuring Mission ◽  
Mountain Ranges ◽  
Low Level ◽  
Atmospheric River ◽  
The Andes ◽  
The Pacific ◽  
Stratiform Clouds ◽  
Orographic Enhancement ◽  
Trmm Precipitation

Abstract Upstream orographic enhancement of the rainfall from an extratropical cyclone approaching the Andes from the Pacific is investigated using the Weather Research and Forecasting (WRF) Model and the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar. The main precipitation from the cyclone over central and coastal Chile fell when a narrow cold-frontal rainband (NCFR) interacted with a midlevel layer cloud deck formed from the orographically induced ascent of the prefrontal “atmospheric river” upstream of the Andes. Model output indicates that low-level convergence enhanced the NCFR where it met low-level blocked flow near the mountains. The NCFR had stronger updrafts with decreasing distance from the mountains, and the NCFR produced larger rain accumulations over the land region upstream of the Andes than over the open ocean. A sensitivity simulation with a 50% reduction in the Andes topography, for comparison to various west coast mountain ranges of North America, demonstrates that the extreme height of the real mountain barrier strengthens frontogenesis and upstream blocking, which produces stronger frontal lifting and a slower progression of the frontal system. The model and the satellite data suggest that the larger precipitation rates upstream of the Andes resulted from a seeder–feeder effect connected with the orographically invigorated NCFR updrafts, when they penetrated the orographically enhanced midlevel stratiform clouds forming as a result of the upstream orographic ascent of the atmospheric river. The supercooled water of the NCFR updrafts formed a feeder zone for the snow particles in the midlevel stratiform cloud just upstream of the Andes.

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