@misc{BendixTrachtePalaciosetal., author = {Bendix, J{\"o}rg and Trachte, Katja and Palacios, Enrique and Rollenbeck, R{\"u}tger and G{\"o}ttlicher, Dietrich and Nauss, Thomas and Bendix, Astrid}, title = {El Ni{\~n}o meets La Ni{\~n}a - anomalous rainfall patterns in the "traditional" El Ni{\~n}o region of Southern Ecuador}, series = {Erdkunde}, volume = {65}, journal = {Erdkunde}, number = {2}, doi = {10.3112/erdkunde.2011.02.04}, pages = {151 -- 167}, abstract = {In this paper, the central Pacific cold event of 2008 and its exceptionally warm conditions in the eastern tropical Pacific are analyzed by using rainfall data of south Ecuadorian meteorological stations, sea surface temperatures in the El Ni{\~n}o3 and 1+2 regions, and simulations with the Weather Research and Forecasting (WRF) model. It can be shown that El Ni{\~n}o-like rainfall conditions with severe inundations occur particularly in the coastal plains of southern Ecuador while a central Pacific cold event prevails. In contrary to previous situations, positive rainfall anomalies as a result of El Ni{\~n}o-like conditions in the El Ni{\~n}o1+2 region during the 2008 La Ni{\~n}a event occurred in both regions, the coastal plains and the highlands, for the first time. A detailed analysis of the ocean-atmosphere system during episodes of heavy rainfall reveals typical El Ni{\~n}o circulation and rainfall patterns as observed during previous El Ni{\~n}o events for the coastal area and La Ni{\~n}a-like conditions for the highlands. The spreading of Pacific instability in the Ni{\~n}o1+2 region to the eastern escarpment of the Andes could be the result of a temporary eastward shift of the Walker circulation. The unusual combination of El Ni{\~n}o-like conditions in the eastern tropical Pacific during a La Ni{\~n}a state in the central Pacific is the newest indicator for an impact mode shift regarding severe rainfall anomalies during El Ni{\~n}o/La Ni{\~n}a events in the traditional El Ni{\~n}o area of southern Ecuador since the end of the last century. Since 2000, El Ni{\~n}o events unexpectedly provide below average rainfall while central Pacific La Ni{\~n}a conditions generate exceptional severe flooding in the normally drier coastal plains. The novel sea surface temperature (SST) anomaly dipole structure between the eastern and central/western tropical Pacific and the weakening of El Ni{\~n}o events since 2000 could be due to natural decadal oscillations in the El Ni{\~n}o background state, the Pacific Decadal Oscillation (PDO). However, the observed atmospheric patterns and the recent increase of the SST anomaly difference between the central and the eastern tropical Pacific resemble structures that also result from climate change simulations.}, language = {en} } @misc{KnerrTrachteGareletal., author = {Knerr, Isabel and Trachte, Katja and Garel, Emilie and Huneau, Fr{\´e}d{\´e}ric and Santoni, S{\´e}bastien and Bendix, J{\"o}rg}, title = {Partitioning of Large-Scale and Local-Scale Precipitation Events by Means of Spatio-Temporal Precipitation Regimes on Corsica}, series = {Atmosphere}, volume = {11}, journal = {Atmosphere}, number = {4}, doi = {10.3390/atmos11040417}, pages = {19}, abstract = {The island of Corsica in the western Mediterranean is characterized by a pronounced topography in which local breeze systems develop in the diurnal cycle. In interaction with the large-scale synoptic situation, various precipitation events occur, which are classified in this study with regard to their duration and intensity. For this purpose, the island was grouped into five precipitation regimes using a cluster analysis, namely the western coastal area, the central mountainous region, the southern coastal area, the northeast coastal area, and the eastern coastal area. Based on principal component analysis using mean sea level pressure (mslp) obtained from ERA5 reanalysis (the fifth generation of the European Centre for Medium-Range Weather Forecasts, ECMWF), six spatial patterns were identified which explain 98\% of the large-scale synoptic situation, while the diurnal breeze systems within the regimes characterize local drivers. It is shown that on radiation days with weak large-scale pressure gradients, pronounced local circulations in mountainous regions are coupled with sea breezes, leading to a higher number of short and intense precipitation events. Meridional circulation patterns lead to more intensive precipitation events on the eastern part of the island (30\% intensive events with meridional patterns on the east side compared to 11\% on the west side). On the west side of Corsica, however, coastal precipitation events are seldom and less intense than further inland, which can be attributed to the influence of the topography in frontal passages.}, language = {en} } @misc{SeidelTrachteOrellanaAlvearetal., author = {Seidel, Jochen and Trachte, Katja and Orellana-Alvear, Johanna and Figueroa, Rafael and C{\´e}lleri, Rolando and Bendix, J{\"o}rg and Fernandez, Ciro and Huggel, Christian}, title = {Precipitation Characteristics at Two Locations in the Tropical Andes by Means of Vertically Pointing Micro-Rain Radar Observations}, series = {Remote Sensing}, volume = {11}, journal = {Remote Sensing}, number = {24}, doi = {10.3390/rs11242985}, pages = {18}, abstract = {In remote areas with steep topography, such as the Tropical Andes, reliable precipitation data with a high temporal resolution are scarce. Therefore, studies focusing on the diurnal properties of precipitation are hampered. In this paper, we investigated two years of data from Micro-Rain Radars (MRR) in Cuenca, Ecuador, and Huaraz, Peru, from February 2017 to January 2019. This data allowed for a detailed study on the temporal precipitation characteristics, such as event occurrences and durations at these two locations. Our results showed that the majority of precipitation events had durations of less than 3 h. In Huaraz, precipitation has a distinct annual and diurnal cycle where precipitation in the rainy season occurred predominantly in the afternoon. These annual and diurnal cycles were less pronounced at the site in Cuenca, especially due to increased nocturnal precipitation events compared to Huaraz. Furthermore, we used a fuzzy logic classification of fall velocities and rainfall intensities to distinguish different precipitation types. This classification showed that nightly precipitation at both locations was predominantly stratiform, whereas (thermally induced) convection occurred almost exclusively during the daytime hours.}, language = {en} } @misc{CarrilloRojasSchulzOrellanaAlvearetal., author = {Carrillo-Rojas, Galo and Schulz, Hans Martin and Orellana-Alvear, Johanna and Ochoa-S{\´a}nchez, Ana and Trachte, Katja and C{\´e}lleri, Rolando and Bendix, J{\"o}rg}, title = {Atmosphere-surface fluxes modeling for the high Andes: The case of p{\´a}ramo catchments of Ecuador}, series = {Science of the Total Environment}, journal = {Science of the Total Environment}, number = {704}, issn = {0048-9697}, doi = {10.1016/j.scitotenv.2019.135372}, abstract = {Interest in atmosphere-surface flux modeling over the mountainous regions of the globe has increased recently, with a major focus on the prediction of water, carbon and other functional indicators in natural and disturbed conditions. However, less research has been centered on exploring energy fluxes (net radiation; sensible, latent and soil heat) and actual evapotranspiration (ETa) over the Neotropical Andean biome of the p{\´a}ramo. The present study assesses the implementation and parameterization of a state-of-art Land-Surface Model (LSM) for simulation of these fluxes over two representative p{\´a}ramo catchments of southern Ecuador. We evaluated the outputs of the LSM Community Land Model (CLM ver. 4.0) with (i) ground-level flux observations from the first (and highest) Eddy Covariance (EC) tower of the Northern Andean p{\´a}ramos; (ii) spatial ETa estimates from the energy balance-based model METRIC (based on Landsat imagery); and (iii) derived ETa from the closure of the water balance (WB). CLM's energy predictions revealed a significant underestimation on net radiation, which impacts the sensible and soil heat fluxes (underestimation), and delivers a slight overestimation on latent heat flux. Modeled CLM ETa showed acceptable goodness-of-fit (Pearson R = 0.82) comparable to ETa from METRIC (R = 0.83). Contrarily, a poor performance of ETa WB was observed (R = 0.46). These findings provide solid evidence on the CLM's accuracy for the ETa modeling, and give insights in the selection of other ETa methods. The study contributes to a better understanding of ecosystem functioning in terms of water loss through evaporative processes, and might help in the development of future LSMs' implementations focused on climate / land use change scenarios for the p{\´a}ramo.}, language = {en} } @misc{CampozanoTrachteCellerietal., author = {Campozano, Lenin and Trachte, Katja and C{\´e}lleri, Rolando and Samaniego, Esteban and Bendix, J{\"o}rg and Albuja, Crist{\´o}bal and Mejia, John F.}, title = {Climatology and Teleconnections of Mesoscale Convective Systems in an Andean Basin in Southern Ecuador: The Case of the Paute Basin}, series = {Advances in Meteorology}, volume = {2018}, journal = {Advances in Meteorology}, number = {3}, doi = {10.1155/2018/4259191}, abstract = {Mesoscale convective systems (MCSs) climatology, the thermodynamic and dynamical variables, and teleconnections influencing MCSs development are assessed for the Paute basin (PB) in the Ecuadorian Andes from 2000 to 2009. *e seasonality of MCSs occurrence shows a bimodal pattern, with higher occurrence during March-April (MA) and October-November (ON), analogous to the regional rainfall seasonality. *e diurnal cycle of MCSs shows a clear nocturnal occurrence, especially during the MA and ON periods. Interestingly, despite the higher occurrence of MCSs during the rainy seasons, the monthly size relative frequency remains fairly constant throughout the year. On the east of the PB, the persistent high convective available potential and low convective inhibition values from midday to nighttime are likely related to the nocturnal development of the MCSs. A significant positive correlation between the MCSs occurrence to the west of the PB and the Trans-Ni{\~n}o index was found, suggesting that ENSO is an important source of interannual variability of MCSs frequency with increasing development of MCSs during warm ENSO phases. On the east of the PB, the variability of MCSs is positively correlated to the tropical Atlantic sea surface temperature anomalies south of the equator, due to the variability of the Atlantic subtropical anticyclone, showing main departures from this relation when anomalous conditions occur in the tropical Pacific due to ENSO.}, language = {en} } @misc{TrachteSeidelFigueroaetal., author = {Trachte, Katja and Seidel, Jochen and Figueroa, Rafael and Otto, Marco and Bendix, J{\"o}rg}, title = {Cross-Scale Precipitation Variability in a Semiarid Catchment Area on the Western Slopes of the Central Andes}, series = {Journal of Applied Meteorology and Climatology}, volume = {57}, journal = {Journal of Applied Meteorology and Climatology}, number = {3}, doi = {10.1175/JAMC-D-17-0207.1}, pages = {675 -- 694}, abstract = {Spatiotemporal precipitation patterns were investigated on the western slopes of the central AndesMountains by applying EOF and cluster analysis as well as the Weather Research and Forecasting (WRF)Model. In the semiarid catchment area in the highlands of Lima, Peru, the precipitation is assumed to be across-scale interplay of large-scale dynamics, varying sea surface temperatures (SSTs), and breeze-dominatedslope flows. The EOF analysis was used to encompass and elucidate the upper-level circulation patternsdominating the transport of moisture. To delineate local precipitation regimes, a partitioning cluster analysiswas carried out, which additionally should illustrate local effects such as the altitudinal gradient of the Andes. Theresults demonstrated that especially during the transition to the dry season, synoptic-scale circulation aloft controlsthe precipitation (correlation coefficients between 0.6 and 0.9), whereas in the remaining seasons the slope breezesdue to the altitudinal gradient mainly determine the precipitation behavior. Further analysis with regard to thespatiotemporal precipitation variability revealed an inversion of the precipitation distribution along the elevationalgradient within the study area, mainly during February (29\%) and March (35\%), that showed correlations withcoastal SST patterns ranging between 0.56 and 0.67. WRF simulations of the underlying mechanisms disclosed thatthe large-scale circulation influences the thermally induced upslope flows while the strength of southeastern low-level winds related to the coastal SSTs caused a blocking of easterlies in the middle troposphere through a reducedanticyclonic effect. This interplay enables the generation of precipitation in the usually drier environment at lower elevations, which leads to a decrease in rainfall with increasing elevation.}, language = {en} } @misc{LehnertThiesTrachteetal., author = {Lehnert, Lukas W. and Thies, Boris and Trachte, Katja and Achilles, Sebastian and Osses, Pablo and Baumann, Karen and Schmidt, Jakob and Samolov, Elena and Jung, Patrick and Leinweber, Peter and Karsten, Ulf and B{\"u}del, Burkhard and Bendix, J{\"o}rg}, title = {A Case Study on Fog/Low Stratus Occurrence at Las Lomitas, Atacama Desert (Chile) as a Water Source for Biological Soil Crusts}, series = {Aerosol and Air Quality Research}, volume = {18}, journal = {Aerosol and Air Quality Research}, number = {1}, issn = {1680-8584}, doi = {10.4209/aaqr.2017.01.0021}, pages = {254 -- 269}, abstract = {The Atacama Desert is well known for the high occurrence of large-scale fog (spatial extents: hundreds of kilometers) emerging as low stratus (LST) decks over the Pacific Ocean. By contrast, the small-scale and heterogeneous occurrence of small-scale fog (hundreds of meters) particularly during summers is widely unconsidered. However, these events are important for the local vegetation and particularly for the biological soil crusts (BSC) that are widely distributed in this extreme ecosystem. Consequently, a case study in a typical fog oasis in the Pan de Az{\´u}car National Park was conducted to test the feasibility combining field measurements, drone profiling, remote sensing and numerical modeling (i) to investigate fog-type specific differences regarding dynamics, physical properties and formation, (ii) to test the applicability of remote sensing technology for fog monitoring based on existing low-resolution and a proposed new high-resolution product and (iii) to estimate the related fog water input to BSCs. Two types of fog were observed. The well-known fog/LST deck emerging from the Pacific Ocean with high water path and large spatial extent was the first type. Fog of the second type was patchier, small-scale and not necessarily connected to the LST over the ocean. Instead, fog formation of the second type was related to thermal breeze systems, which produced shallow clouds containing less water than those of type 1. In general, such small-scale fog events were not captured well by existing remote sensing products but could be detected with the proposed new high-resolution product which provided promising results. Both fog types were important water resources for the BSCs, with approximately 8\% to 24\% of the fog water flux available to the BSCs at the surface. The results indicated the feasibility of the proposed methods' pool to estimate the water budget of BSCs with a high spatial resolution in the future.}, language = {en} } @misc{BendixFriesZarateetal., author = {Bendix, J{\"o}rg and Fries, Andreas and Z{\´a}rate, Jorge and Trachte, Katja and Rollenbeck, R{\"u}tger and Pucha-Cofrep, Franz and Paladines, Renzo and Palacios, Ivan and Orellana-Alvear, Johanna and O{\~n}ate-Valdivieso, Fernando and Naranjo, Carlos and Mendoza, Leonardo and Mejia, Diego and Guallpa, Mario and Gordillo, Francisco and Gonzalez-Jaramillo, Victor and Dobbermann, Maik and C{\´e}lleri, Rolando and Carrillo, Carlos and Araque, Augusto and Achilles, Sebastian}, title = {RadarNet-Sur First Weather Radar Network in Tropical High Mountains}, series = {Bulletin of the American Meteorological Society}, volume = {98}, journal = {Bulletin of the American Meteorological Society}, number = {6}, doi = {10.1175/BAMS-D-15-00178.1}, pages = {1235 -- 1254}, abstract = {Weather radar networks are indispensable tools for forecasting and disaster prevention in industrialized countries. However, they are far less common in the countries of South America, which frequently suffer from an underdeveloped network of meteorological stations. To address this problem in southern Ecuador, this article presents a novel radar network using cost-effective, single-polarization, X-band technology: the RadarNet-Sur. The RadarNet-Sur network is based on three scanning X-band weather radar units that cover approximately 87,000 km2 of southern Ecuador. Several instruments, including five optical disdrometers and two vertically aligned K-band Doppler radar profilers, are used to properly (inter) calibrate the radars. Radar signal processing is a major issue in the high mountains of Ecuador because cost-effective radar technologies typically lack Doppler capabilities. Thus, special procedures were developed for clutter detection and beam blockage correction by integrating ground-based and satelliteborne measurements. To demonstrate practical applications, a map of areas frequently affected by intense rainfall is presented, based on a time series of one radar that has been in operation since 2002. Such information is of vital importance to, for example, infrastructure management because rain-driven landslides are a major issue for road maintenance and safety throughout Ecuador. The presented case study of exceptionally strong rain events during the recent El Ni{\~n}o in March 2015 highlights the system's practicality in weather forecasting related to disaster management. For the first time, RadarNet-Sur warrants a spatial-explicit observation of El Ni{\~n}o-related heavy precipitation in a transect from the coast to the highlands in a spatial resolution of 500 m.}, language = {en} } @misc{MakowskiGiannoniTrachteRollenbecketal., author = {Makowski Giannoni, Sandro and Trachte, Katja and Rollenbeck, R{\"u}tger and Lehnert, Lukas W. and Fuchs, Julia and Bendix, J{\"o}rg}, title = {Atmospheric salt deposition in a tropical mountain rainforest at the eastern Andean slopes of south Ecuador - Pacific or Atlantic origin?}, series = {Atmospheric Chemistry and Physics}, volume = {16}, journal = {Atmospheric Chemistry and Physics}, number = {15}, doi = {10.5194/acp-16-10241-2016}, pages = {10241 -- 10261}, abstract = {Sea salt (NaCl) has recently been proven to be of the utmost importance for ecosystem functioning in Amazon lowland forests because of its impact on herbivory, litter decomposition and, thus, carbon cycling. Sea salt deposition should generally decline as distance from its marine source increases. For the Amazon, a negative east-west gradient of sea salt availability is assumed as a consequence of the barrier effect of the Andes Mountains for Pacific air masses. However, this generalized pattern may not hold for the tropical mountain rainforest in the Andes of southern Ecuador. To analyse sea salt availability, we investigated the deposition of sodium (Na+) and chloride (Cl-), which are good proxies of sea spray aerosol. Because of the complexity of the terrain and related cloud and rain formation processes, sea salt deposition was analysed from both, rain and occult precipitation (OP) along an altitudinal gradient over a period between 2004 and 2009. To assess the influence of easterly and westerly air masses on the deposition of sodium and chloride over southern Ecuador, sea salt aerosol concentration data from the Monitoring Atmospheric Composition and Climate (MACC) reanalysis data set and back-trajectory statistical methods were combined. Our results, based on deposition time series, show a clear difference in the temporal variation of sodium and chloride concentration and Na+ ∕ Cl- ratio in relation to height and exposure to winds. At higher elevations, sodium and chloride present a higher seasonality and the Na+ ∕ Cl- ratio is closer to that of sea salt. Medium- to long-range sea salt transport exhibited a similar seasonality, which shows the link between our measurements at high elevations and the sea salt synoptic transport. Although the influence of the easterlies was predominant regarding the atmospheric circulation, the statistical analysis of trajectories and hybrid receptor models revealed a stronger impact of the north equatorial Atlantic, Caribbean, and Pacific sea salt sources on the atmospheric sea salt concentration in southern Ecuador. The highest concentration in rain and cloud water was found between September and February when air masses originated from the north equatorial Atlantic, the Caribbean Sea and the equatorial Pacific. Together, these sources accounted for around 82.4 \% of the sea salt budget over southern Ecuador.}, language = {en} } @misc{LehnertWescheTrachteetal., author = {Lehnert, Lukas W. and Wesche, Karsten and Trachte, Katja and Reudenbach, Christoph and Bendix, J{\"o}rg}, title = {Climate variability rather than overstocking causes recent large scale cover changes of Tibetan pastures}, series = {Scientific Reports}, volume = {6}, journal = {Scientific Reports}, number = {1}, doi = {10.1038/srep24367}, abstract = {The Tibetan Plateau (TP) is a globally important "water tower" that provides water for nearly 40\% of the world's population. This supply function is claimed to be threatened by pasture degradation on the TP and the associated loss of water regulation functions. However, neither potential large scale degradation changes nor their drivers are known. Here, we analyse trends in a high-resolution dataset of grassland cover to determine the interactions among vegetation dynamics, climate change and human impacts on the TP. The results reveal that vegetation changes have regionally different triggers: While the vegetation cover has increased since the year 2000 in the north-eastern part of the TP due to an increase in precipitation, it has declined in the central and western parts of the TP due to rising air temperature and declining precipitation. Increasing livestock numbers as a result of land use changes exacerbated the negative trends but were not their exclusive driver. Thus, we conclude that climate variability instead of overgrazing has been the primary cause for large scale vegetation cover changes on the TP since the new millennium. Since areas of positive and negative changes are almost equal in extent, pasture degradation is not generally proceeding.}, language = {en} }