This study analyzes the cloud properties associated with cold fronts that affected central Chile during May–September 1998–2014 using observational and reanalysis data. Warmer, moister, and more ...unstable conditions in early winter favor the development of deeper mixed‐phased clouds in cold fronts, having larger rain and ice water contents. Late in the season, cooler, drier, and more stable conditions predominate, favoring the development of a larger percentage of shallower warm‐phased clouds. Years when cold fronts show large environmental humidity and high cloud tops were associated with stronger systems that produced the largest precipitation. The linear positive relationship between cloud tops and precipitable water reported in the Central and Eastern Pacific was also found in storms developing in the Eastern South Pacific. The intensity of cold fronts also determines their cloud development and observed rainfall. High freezing level (FL) cold fronts are more frequent in May and June, generally occur in very high humidity environments, are stronger, include more rain and ice water contents, and allow the development of the highest clouds compared to low FL storms, which are more frequent in August. The strength of low FL storms, instead of their available humidity seems to be the key factor controlling the rain they produce. On the other hand, the intensity of high FL storms seems not to be a decisive factor in controlling its rainfall. Finally, the presence of an atmospheric river seems not to guarantee the rainiest events among high and low FL cold fronts.
Key Points
Cold fronts find the wettest, least stable environment in May, causing the highest clouds and large rainfall. Conditions worsen afterwards
High freezing level (FL) cold fronts develop in high humidity environments, are stronger, and produce more rainfall than low FL cold fronts
The strength of low FL cold fronts seems to be a key factor modulating the transition from weak‐storm‐low‐rain to strong‐storm‐large‐rain
This study evaluates the performance of fourteen high-resolution WRF runs with different combinations of parameterizations in simulating the atmospheric conditions over the complex terrain of central ...Chile during austral winter and spring. We focus on the validation of results for coastal, interior valleys, and mountainous areas independently, and also present an in-depth analysis of two synoptic-scale events that occurred during the study period: a frontal system and a cut-off low. The performance of the simulations decreases from the coast to higher altitudes, even though the differences are not very clear between the coast and interior valleys for 10 m wind speeds and precipitation. The simulated vertical profiles show a warmer and drier boundary layer and a cooler and moister free atmosphere than observed. The choice of the land-surface model has the largest positive impact on near-surface variables with the five-layer thermal diffusion scheme showing the smallest errors. Precipitation is more sensitive to the choice of cumulus parameterizations, with the simplified Arakawa–Schubert scheme generally providing the best performance for absolute errors. When examining the performance of the model simulating rain/no-rain events for different thresholds, also the cumulus parameterizations better represented the false alarm ratio (FAR) and the bias score (BS). However, the Morrison microphysics scheme resulted in the best critical success index (CSI), while the probability of detection (POD) was better in the simulation without analysis nudging. Overall, these results provide guidance to other researchers and help to identify the best WRF configuration for a specific research or operational goal.
The Radiative Heating in Underexplored Bands Campaign (RHUBC-II) project was held from August to October 2009 in the Atacama Desert in Chile at 5320-m altitude. Observations from this experiment and ...a high-resolution numerical simulation with the Weather Research and Forecasting Model (WRF) were used to understand the structure and evolution of the atmosphere over a region with complex terrain and extremely dry environmental conditions. The mechanisms driving the local circulations during synoptically unperturbed conditions at the field site were studied. The study suggests that the field site is mainly affected by a mountain-scale and a plateau-scale thermally driven circulation. The latter seems to dominate. The advection of warm air by downslope flows from higher heights during nighttime may be the mechanism that counteracts the longwave radiative cooling at the surface, causing a small decrease of near-surface temperature during the night. WRF represents the near-surface and upper atmosphere reasonably well above the RHUBC-II site. Important orographic features are misrepresented in the model terrain, which may cause the observed differences in near-surface winds. The zonal pressure gradient between both sides of the mountain and the static stability of the air mass on the windward side of the terrain control the local circulations over the field site. Consequently, a misrepresentation of these mechanisms in the model may cause differences between the simulated winds and observations.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The Cherenkov Telescope Array (CTA) in the southern hemisphere will be installed at Armazones 2k site in northern Chile. Scarce atmospheric observations are available in the region, particularly ...radiosonde data. This study analyzes radiosondes launched at Paranal observatory, located at about 21 km from the CTA site, from 24 October and 4 November 2011, to understand the behavior of density in the atmosphere near the CTA site. High-resolution numerical simulations with the Weather Research and Forecasting (WRF) model are validated with Paranal radiosondes to quantify its ability to represent the atmospheric conditions in the region. In addition, the seasonal and diurnal evolution of atmospheric density at the CTA site were studied during 2011 using the high-resolution weather forecasts from the WRF model.
El objetivo de la investigación fue determinar la relación existente entre la Autoeficacia Académica y la Procrastinación Académica en una muestra de adolescentes de la ciudad de Quito, Ecuador. La ...investigación presenta un enfoque descriptivo, correlacional de corte transversal por medio de las escalas de Procrastinación Académica, Procrastinación Académica de Tuckman, Autoeficacia General y Autoeficacia Percibida Específica de Situaciones Académicas. Participaron 424 adolescentes (49,8% hombres, 50,2% Mujeres) entre 12 a 17 años (M= 14 años; DT= 1,71). Estudiantes de diversas instituciones educativas secundarias (73,8% privado, 25,2% pública y 0,9% Fiscomisional) de la ciudad de Quito, Ecuador. La Autoeficacia General y Académica es moderada, mientras que la Procrastinación es baja; únicamente se presentan diferencias por género en la Autoeficacia General, siendo los hombres quienes evidencian más autoeficacia. Existe relación entre la Autoeficacia Académica y la Procrastinación Académica. En conclusión, la Autoeficacia Académica es un factor relevante que permite identificar el desempeño de la Procrastinación Académica en adolescentes de la ciudad de Quito.
Abstract Tornadoes in Chile seem to develop in what are called “high-shear, low-CAPE” (HSLC) environments. An analysis of convective parameters from the ERA5 reanalysis during 16 notable tornadoes in ...Chile showed that several increased markedly before the time of the reports. The significant tornado parameter (STP) was able to discriminate the timing and location of the tornadoes, even though it was not created with that goal. We established thresholds for the severe hazards in environments with reduced buoyancy (SHERBE) parameter (≥1) and the STP (≤−0.3) to further identify days favorable for tornado activity in Chile. The SHERBE and STP parameters were then used to conduct a climatological analysis from 1959 to 2021 of the seasonal, interannual, and latitudinal variations of the environments that might favor tornadoes. Both parameters were found to have a strong annual cycle. The largest magnitudes of STP were found to be generally confined to south-central Chile, in agreement with the (sparse) tornado record. The probability of a day with both SHERBE and STP values beyond their thresholds was greatest between May and August, which aligns with the months with the most tornado reports. The number of days with both SHERBE and STP beyond their respective thresholds was found to fluctuate interannually. This result warrants further study given the known interannual variability of synoptic and mesoscale weather in Chile. The results of this study extend our understanding of tornado environments in Chile and provide insight into their spatiotemporal variability.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Tornadoes were reported in south-central Chile on 30 and 31 May 2019. To better understand the mechanisms that supported the organization and severity of the storms that generated them, a series of ...high-resolution sensitivity simulations were conducted using the Weather Research and Forecast (WRF) model. In addition to a control simulation, three simulations were run that successively reduced the topography to 50%, 25%, and 0% of original height; three more simulations were run that increased SST by 2 K everywhere, decreased it by 2 K everywhere, and set all SSTs greater than 16 °C to exactly 16 °C; finally, two more simulations were run to explore the combined effects of SST changes and lower topography.
Results indicate that as topography was lowered, a strong northerly low-level jet along the upslope of the Andes weakened and broadened in both vertical and horizontal extent. Values of 0–6-km bulk shear and 0–3-km storm-relative helicity (SRH) over the regions where the tornadoes occurred diminished with successive reduction of the topography. As a result, simulated brightness temperatures were warmer, and swaths of updraft helicity were fewer and shorter. These results indicate that on 30–31 May 2019, flow blocking by the Andes topography generated mesoscale wind shear conditions that favored tornadoes. When SSTs were increased, instability (quantified by convective available potential energy, CAPE) also increased, although primarily offshore, and updraft helicity swath length increased, indicating a positive impact on simulated storm intensity. When SSTs were decreased, CAPE also decreased along with a decline in magnitude of updraft helicity. These results suggest that SSTs also impact storm severity via an influence on atmospheric instability. When the two factors were combined, warmer SSTs were not able to overcome a reduction in wind shear associated with a decrease in the topography. This suggests that in south-central Chile, wind shear is more important than CAPE for tornadic thunderstorms, as has been found for other regions around the world).
•The low-level wind regime is modified by the Andes, generating favorable conditions for tornado formation.•SSTs impact storm severity by increasing atmospheric instability.•Wind shear seems to be more important for tornadic thunderstorms in south-central Chile than CAPE.
Color cinematography has ignited debates about how color should be used, and what color aesthetics can add to cinema. While Technicolor's aesthetics required painstakingly designed artificial ...lighting to achieve naturalist effects, Daughters of the Dust (Julie Dash, 1991) uses primarily natural lighting to produce a surreal colorscape I call water color. This radical aesthetics of color disrupts classical notions about color and cinema in several ways: it supports Dash's radical feminist narrative style, challenges the purity of whiteness and the notion that dark skin tones are difficult to film, and historicizes the power relations of color pigment production.
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