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Título del pre-print: Precipitation characterization of northern Chile using weather regimes ; Northern Chile is one of the most arid regions in the world, with precipitation mainly occurring during austral summer, between December and April. The aim of this study is to classify the main weather regimes derived from sea level pressure, surface wind speed, 500 or 250 hPa geopotential heights, in order to measure their influence on precipitation anomalies and determine if they can be considered sources of predictability of rainfall in this region. Four weather regimes were found to optimally describe atmospheric circulation in the study area during 1966-2015 and for each of the four levels described above. Using daily precipitation data from a network of 161 meteorological stations across the region, the rainfall anomalies associated with each weather regime were quantified. They are coherent with the direction of flow derived from pressure and geopotential anomalies, bringing humid air masses from the Amazon Basin or the Pacific. The transitions between the different regimes are also coherent, representing transitions to and from similar regimes. A few negative and significant trends in the persistence of different regimes were detected, most likely linked to the absence of anthropogenic warming in the Antarctic as opposed to the Arctic. Finally, two of the regimes derived from surface wind speed exhibit a negative and significant trend in its frequency of occurrence, determining a precipitation decrease in the south of the study area (28–30°S), which can be compared with the Megadrought experienced in central Chile. ; The authors want to thank the support of the FONDECYT Project 11160059 (Chilean Government), the Climatology Group (2017 SGR 1362, Catalan Government), the Spanish Ministry of Economy and Competitiveness (MINECO) as part of the Juan de la Cierva - Incorporación grant (BOE-A-2010-3694), the New European Wind Atlas (NEWA) project (PCIN-2016-029), the Subseasonal to Seasonal for Energy (S2S4E) project ...

Daily time series from the Climate Prediction Center (CPC) Africa Rainfall Climatology version 2.0 (ARC2), Climate Hazards Group InfraRed Precipitation with Stations (CHIRPS) and Tropical Applications of Meteorology using SATellite (TAMSAT) African Rainfall Climatology And Time series version 2 (TARCAT) high-resolution long-term satellite rainfall products are exploited to study the spatial and temporal variability of East Africa (EA, 5S–20N, 28–52E) rainfall between 1983 and 2015. Time series of selected rainfall indices from the joint CCl/CLIVAR/JCOMM Expert Team on Climate Change Detection and Indices are computed at yearly and seasonal scales. Rainfall climatology and spatial patterns of variability are extracted via the analysis of the total rainfall amount (PRCPTOT), the simple daily intensity (SDII), the number of precipitating days (R1), the number of consecutive dry and wet days (CDD and CWD), and the number of very heavy precipitating days (R20). Our results show that the spatial patterns of such trends depend on the selected rainfall product, as much as on the geographic areas characterized by statistically significant trends for a specific rainfall index. Nevertheless, indications of rainfall trends were extracted especially at the seasonal scale. Increasing trends were identified for the October–November–December PRCPTOT, R1, and SDII indices over eastern EA, with the exception of Kenya. In March–April–May, rainfall is decreasing over a large part of EA, as demonstrated by negative trends of PRCPTOT, R1, CWD, and R20, even if a complete convergence of all satellite products is not achieved. ; This study was supported by the European Union's Seventh Programme for research, technological development, and demonstration under Grant Agreement 603608 (eartH2Observe).

Abstract. This work presents a catalog of daily precipitation fields in the Balearic Islands created with data from AEMET (State Meteorological Agency) assistant observations, including records from 1912. The original digital daily data file has been interpolated onto a regular 100 m-resolution grid (namely PREGRIDBAL), defined with the aim of becoming a valid standard for future methodological improvements and catalog upgrades. Daily precipitation amounts on each grid point are calculated using an analysis method based on ordinary kriging, using the daily anomaly with respect to the annual mean for all available observations each day. Due to quality concerns, the time span for products derived from the catalog is limited to the 1950–2009 period, when the number of operating stations reached 200. Therefore, from the time series of daily maps, monthly-, annual-, quinquennial-, and decadal-accumulations are produced. Similarly, the catalog allowed for quantification of climate trends in rainfall amounts in the Balearic Islands, with the significant advantage of minimizing the biases originated from heterogeneities in the spatial distribution of stations across the archipelago. Results show a general decrease in precipitation during the 1950–2009 period. From 1950 to 1979, the average annual precipitation across the islands was 624.3 mm, while from 1980 to 2009 it diminished to 555.36 mm. Changes in precipitation patterns, which vary among the different areas, are also detected. The most significant reductions are found in the northern half of the archipelago and especially in Mallorca, where the Tramuntana mountain range stands out. All seasonal trends show a decrease, with values ranging between 1 and 3 mm decade−1, with the exception of autumn, which reaches a positive trend up to 7 mm decade−1. October shows the most dramatic decrease (−10. 34 mm decade−1) and, conversely, September and November show an increase in precipitation (3.28 and 1.82 mm decade−1, respectively) with a statistical significance above 85 % across almost the entire archipelago, and even exceeding 95 % in Eivissa and Formentera.

Póster elaborado para la European Geosciences Union General Assembly, celebrada en Viena del 3 al 8 de abril de 2011 ; This research was supported by the Spanish Ministry of Science and Innovation project NUCLIERSOL (CGL2010- 18546). The first author was granted by a postdoctoral position funded by the government of Catalonia (2009 BP-A 00035).

Northern Chile is one of the most arid regions in the world, as it includes the Atacama Desert. At high elevations, most precipitation is observed only during a short period of the year, from December until March. This renders water availability a major concern for policymakers. Accumulated rainfall varies considerably from one year to another, and for this reason, climate projections have a very low degree of confidence in this area. Consequently, in this region, it is more interesting to study the irregularity of precipitation itself than accumulated rainfall values, as they express in a clearer way the behaviour of precipitation. According to daily data from 161 meteorological stations, four irregularity indices of precipitation were calculated: concentration index, entropy, persistence index, and fractal dimension. These indices were measured according to observed values, and their spatial distribution was subsequently determined by interpolating following multivariate regression models that consider different geographical variables such as latitude, distance to the Amazon Basin, elevation, orientation, and curvature. The temporal trends of each index and for each meteorological station were also calculated, displaying different results depending on the latitude and elevation. These changes agree with the observed modifications on the inter‐tropical atmospheric circulation and with changes in the precipitation diurnal cycle. These results will help improve climate projections for this region, in the process facilitating the development of more accurate climate models and informing the formulation of water management policies. ; The authors want to thank the FONDECYT Project 11160059, the CLICES Project (CGL2017‐83866‐C3‐2‐R), and the Climatology Group (2017 SGR 1362, Catalan Government) for their support.

Póster presentado en: EGU General Assembly 2018 celebrada del 8 al 13 de abril en Viena, Austria. ; The current global climate research has traditionally focused on changes in air temperature and precipitation. As a key climate parameter, changes of winds have a very significant impact on the environment, such as soil wind erosion, air pollution diffusion, wind power energy, etc. In particular, changes of extreme wind speed (i.e., wind gusts) are poorly analyzed and deserve further investigation. In this study we assess trends in máximum wind speed (MWS) across China for 1975-2016, using observed daily wind datasets, and also analyze its relationship with the East Asian monsoon. The raw observed MWS dataset was subject to aquality control and robust homogenization protocol using the Climatol package. The results reveal a statistically significant (p0.10). Even though MWS declines dominated across much of the country through out the year, only as mal number of stations showed statistically significant negative trends in summer (37.7 %) and spring (29.0 %). Our preliminary analyses show that the weakened East Asian monsoon, particularly in winter, positively correlates with the observed changes in MWS. However, statistical significant correlations are too few and further attribution analyses are strongly needed. ; This research is funded by (i) the National Natural Science Foundation of China (Grant No.41621061); (ii) the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant (Grant No. 703733); and (iii) the Swedish Research Council by the project "Detection and attribution of changes in extreme wind gusts over land" (2017-03780).

A mesoscale simulation for Majorca Island is made using the Méso-NH model for a spring night, under a slack synoptic pressure gradient with weak general winds and clear skies. The circulations over and around the island are driven mostly by the locally generated flows, due to the topography and the land–sea thermal contrast. The verification of mesoscale simulations in clear-sky conditions is difficult, especially if the network of stations is not very dense. The main objective of this work is to try to verify the mesoscale simulation using measurements from automatic weather stations and satellite measurements. The model outputs are compared with the available instrumental data and the representativeness of the stations is discussed. Furthermore, complete two-dimensional comparisons are made between the radiative surface temperatures produced by the model and those processed from the National Oceanic and Atmospheric Administration and Meteosat Second Generation (MSG) satellite sensors. The high temporal resolution of the MSG images also allows comparison of the temporal evolutions of the surface temperature between satellite pixels and model grid cells. The procedure permits assessment of the closeness of the simulation to in situ and remote sensing observations. The results of the comparison show that the model is able to reproduce most of the observed patterns, such as intense local cooling or persistent outflows at the largest basins. ; Funding was provided by the Spanish Government (Research Projects REN2003-09435, CGL2005-07105, and CGL2006-12474).

Póster presentado en: EMS Annual Meeting - European Conference for Applied Meteorology and Climatology 2018, celebrado en Budapest del 3 al 7 de septiembre de 2018. ; This study analyzes the variability of winter haze days and visibility in the Beijing-Tianjin-Hebei (BTH) region in relation to wind speed changes in the lower troposphere and emissions for 1961-2014. Daily surface meteorological data, NCEP/NCAR atmospheric reanalysis data, and fossil fuel emission data are used in this research. The results reveal a significant increase in winter haze days of +0.8 days decade-1 (p<0.01), and a subsequent decline in visibility of-1.56 km decade-1 (p<0.01). Most interestingly, an accelerated increase in haze days was observed for the last 11-year period (+8.3 days decade-1) of the study (2004-2014). The increase of winter haze occurrence and decrease in visibility are partly attributed to: the significant (p<0.01) declining trend of mean wind speed at the near-surface (-0.19 m s-1 decade-1), 925hPa (-0.23 m s-1 decade-1), and 850hPa (-0.21 m s-1 decade-1); the vertical shear of wind between 1000hPa and 850hPa (-0.07 m s-1 decade-1); and, the declining (dust storm frequency as a proxy,-0.41 days dec-1) surrounding particulate sources and increasing fossil fuel emissions (total carbon emission as a proxy, +4820.6 metric tons dec-1). Specifically, wind speed changes in the lower troposphere explain 41.3% of winter haze days and 71.2% of the visibility variance. These are extended to 51.7% and 81.6% respectively when combined with natural (dust storm frequency) and anthropogenic (fossil fuel emissions) particulate sources. Therefore, the analyses show that wind speed changes in the lower troposphere, together with the varied natural and anthropogenic sources of particulates, play a key role in modulating winter haze and visibility conditions in the BTH area. ; This research is funded by the National Natural Science Foundation of China (Grant No.41621061), and funding from the European Union's Horizon 2020 ...

An experimental field campaign took place in September 2013 near the coastline in the southeastern Campos basin in the island of Mallorca to characterize experimentally the transition between the sea and land breezes and to further study the successful cases with the corresponding high-resolution numerical simulations. Favorable weather conditions were only found for one episode that comprised a well formed nocturnal land breeze, followed by the morning transition to sea-breeze until noon the next day, when incoming clouds switched off the breeze regime. To analyse this transition between land and sea breezes the official network of stations is used, supplemented by a portable station close to the shore and soundings of temperature (taken by a captive balloon and remotely controlled multicopter). These data are used to check the goodness of the corresponding simulation at a horizontal resolution of 1 km. Model and observations see similarly both regimes and the transition, showing some differences in the timing and the details in the surface layer. This transient event is analyzed in terms of phases, going consecutively through land-breeze, phase previous to the sea breeze, when land heating starts but it is still colder than the sea, the preparatory phase when the land becomes warmer than the sea, and the development phase when the breeze front progresses inland. ; This work was funded through the projects CGL2009-12797-C03-01 and CGL2012-37416-C04-01 of the Spanish Government, supplied by the European Regional Development Fund (FEDER)

According to the Intergovernmental Panel on Climate Change (IPCC), Northern Chile will be one of the most affected territories by changes in the atmospheric dynamics in next years. These climate change effects will be noticed in several ways, and temperatures will be one of the most sensitive variables to these changes, and with high importance because of their relationship with the hydrological cycle in one of the most arid regions in the world. Extreme temperatures of 77 observatories have been analysed by the calculation of 14 indices and their temporal trends. Also, the relationship of these indices between them, between observatories, with elevation and latitude has been taken into consideration, while they imply significant differences of the behaviour of the analysed indices. The results showed general warming trends but with particular differences depending on the behaviour of minimum temperatures. Examining the relationship between the indices and elevation, it appears that this variable has more implications in minimum temperatures. The analysis showed significant correlations also between the indices and latitude, agreeing with not evident general warming trends in the intertropical area of Northern Chile. Considering the different behaviours of the trends and their relationships with latitude and elevations, it has to be analysed in the future the possible existing relations with the spatial and temporal changes in the hydrological cycle such as precipitations. ; The authors want to thank the FONDECYT Project 11160059, the UTA-Mayor Project 5755-17, the CLICES Project (CGL2017-83866-C3-2-R) and the Climatology Group (2014SGR300, Catalan Government).

Póster presentado en: EGU General Assembly 2019 celebrada del 7 al 12 de abril en Viena, Austria. ; The Wind erosion in arid and semi-arid areas is an important global environmental issue, and changes in wind speed trends over time play a key role in wind erosion dynamics. In a warming climate, scientists have recently observed a widespread decline in wind speed, termed "stilling". Here, we apply the Revised Wind Erosion Equation Model (RWEQ) to simulate the variability of wind erosion and quantify the impact of wind speed changes on soil degradation dynamics over the eastern agro-pastoral transitional zone of Northern China (EANC) from 1982 to 2016. Our results show that a significant (i.e., p<0.05) decrease (-0.007 m s-1 year-1) of near-surface wind speed was observed annually, with significant declining trends in spring (-0.010 m s-1 year-1 )and autumn (-0.009 m s-1 year-1). At the same time, wind erosion simulations reveal a negative trend for the annual soil loss from wind erosion (SLWE,-6.20 t hectare-2 year-1 , p<0.05; affecting 99.8% of the study region), with significant declining trends in all seasons, particularly in spring (-3.49 t hectare-2 year-1) and autumn (-1.26 hectare-2 year-1). Further, we isolate the effects of wind variability on wind erosion (SLWED) from 1982 to 2016 by the model variable control method. This shows that wind speed variability strongly weakens wind erosion at-8.14 t hectare-2 year-1 (p<0.05) annually, with the strongest stilling recorded in spring leading to major decreases of wind erosion in spring (-4.77 t hectare-2 year-1 , p<0.05). Meanwhile, the weakest stilling in summer had the opposite influence on wind erosion (+0.40 t hectare-2 year-1 , p<0.10). To summarize, our findings have shown a significant impact of wind stilling on the decline of soil erosion rates in Northern China. ; This research is funded by the National Natural Science Foundation of China (Grant No. 41621061), and funding from the European Union's Horizon 2020 research and innovation ...

Assessing change in daily maximum wind speed and its likely causes is crucial for many applications such as wind power generation and wind disaster risk governance. Multidecadal variability of observed near-surface daily maximum wind speed (DMWS) from 778 stations over China is analyzed for 1975–2016. A robust homogenization protocol using the R package Climatol was applied to the DMWS observations. The homogenized dataset displayed a significant (p 0.10); that is, DMWS declined during the cold semester (October–March) and increased during the warm semester (April–September). Correlation analysis of the Arctic Oscillation, the Southern Oscillation, and the west Pacific modes exhibited significant correlation with DMWS variability, unveiling their complementarity in modulating DMWS. Further, we explored potential physical processes relating to the atmospheric circulation changes and their impacts on DMWS and found that 1) overall weakened horizontal airflow [large-scale mean horizontal pressure gradient (from −0.24 to +0.02 hPa decade−1) and geostrophic wind speed (from −0.6 to +0.6 m s−1 decade−1)], 2) widely decreased atmospheric vertical momentum transport [atmospheric stratification thermal instability (from −3 to +1.5 decade−1) and vertical wind shear (from −0.4 to +0.2 m s−1 decade−1)], and 3) decreased extratropical cyclones frequency (from −0.3 to 0 month decade−1) are likely causes of DMWS change. ; This study was supported by the National Natural Science Foundation of China (Grant 41621061), the National Key Research and Development Program–Global Change and Mitigation Project (Grant 2016YFA0602404), funding from STINT (CH2015-6226), and the European Union's Horizon 2020 research and innovation ...

Northern Chile is a region characterised by an extremely dry climate; however, there is a brief rainy season from December to March (austral summer), mainly above 3000 m a.s.l. It is interesting to consider where the humid air masses that generate such rain come from. For this purpose, daily precipitation data from 161 meteorological stations located in this area (18° S–19° S) were considered, and four clusters formed by k-means clustering. For each cluster, days of extreme precipitation (above 90th percentile) were selected to obtain flow strength (F), direction (D), and vorticity (Z) for each event according to the Jenkinson and Collison (JC) method. The back trajectory, for the previous 72 h, of air masses affecting the centroid of each cluster was determined by means of the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model. The analyses were carried out at sea level (1013 hPa) and in the middle (500 hPa) and upper (250 hPa) troposphere. Surface circulation was not a determining factor in the occurrence of extreme events, but it did influence circulation at 500 and 250 hPa. For stations located in the northern Altiplano, moisture advection from the Amazon basin is evident due to the configuration of the Bolivian high—an upper level anticyclone that develops over the Bolivian Altiplano during austral summer. For stations located in the southern part of the study area, the main source of moisture is the Pacific Ocean, and the weather is related to the arrival of frontal systems and to the configuration of cut-off low pressure systems in the mid-troposphere. ; The authors want to thank the FONDECYT Project 11160059 of the Chilean Government, the Climatology Group (2017SGR1362, Catalan Government) and the CLICES Project (CGL2017-83866-C3-2-R) for the institutional support. R.S.N. is funded by the Spanish Ministry of Science and Innovation (grant no. FJCI-2017-31595).

Póster presentado en: AGU Fall Meeting celebrado en San Francisco del 15 al 19 de diciembre de 2014. ; This work was supported by the Ministry of Economy and Competitiveness of the Government of Spain through the projects NUCLIERSOL (CGL2010-18546) and HIDROCAES (CGL2011-27574-CO2-02). The first author was supported by the "Secretaria per a Universitats i Recerca del Departament d'Economia i Coneixement, de la Generalitat de Catalunya i del programa Cofund de les Accions Marie Curie del 7è Programa marc d'R+D de la Unión Europea" (2011 BP-B 00078) and the postdoctoral fellowship JCI-2012-12508. ASR received a grant from the FPU program (FPU AP2010-0917) of the Spanish Ministry of Education.

The COST (European Cooperation in Science and Technology) Action ES0601: advances in homogenization methods of climate series: an integrated approach (HOME) has executed a blind intercomparison and validation study for monthly homogenization algorithms. Time series of monthly temperature and precipitation were evaluated because of their importance for climate studies and because they represent two important types of statistics (additive and multiplicative). The algorithms were validated against a realistic benchmark dataset. The benchmark contains real inhomogeneous data as well as simulated data with inserted inhomogeneities. Random independent break-type inhomogeneities with normally distributed breakpoint sizes were added to the simulated datasets. To approximate real world conditions, breaks were introduced that occur simultaneously in multiple station series within a simulated network of station data. The simulated time series also contained outliers, missing data periods and local station trends. Further, a stochastic nonlinear global (network-wide) trend was added. ; This study has been performed with support of the European Union, through the COST Action ES0601 – Advances in Homogenisation Methods of Climate Series: an Integrated Approach (HOME), as well as the project Large Scale Climate Changes and their Environmental Relevance funded by the North Rhine-Westphalia Academy of Science. The contribution of VV was supported by the surrogate cloud project (VE 366/3), the one of RL by the Daily Stew project (VE366/5), both sponsored by the German Science Foundation (DFG). The contribution of EA was sponsored by the "Cambios en la Frecuencia, Intensidad y Duracion de eventos Extremos en la Península Ibérica", code number: CGL2007-65546-C03-02.