Papers by Jose A Rutllant
AGU Fall Meeting Abstracts, Dec 1, 2011
The present paper analyzed the large-scale aspects of the atmospheric circulation features during... more The present paper analyzed the large-scale aspects of the atmospheric circulation features during the TOGA-COARE IOP period (November 1, 1992-February 28, 1993). Atmospheric conditions were in many ways similar to those typical of a developing warm episode over the equatorial eastern Pacific, including the frequent occurrence of the low-level westerly wind or westerly wind bursts and the upper-level easterly wind in the western and central Pacific, a moderate eastward shift of the major atmospheric heat source in winter and the Walker circulation, and continuous eastward propagation of 30-60 day low-frequency oscillation into the central and eastern Pacific.
Other Mini-Meetings, Apr 6, 1999
Journal of Arid Environments, Mar 1, 2021
Abstract The impact of future climate change on the native vegetation of subtropical Andes is rel... more Abstract The impact of future climate change on the native vegetation of subtropical Andes is relatively unknown. The semiarid region of north-central Chile (30–34°S) has experienced a mega-drought over the last decade, with a partial recovery during the 2015 El Nino year. To characterize the vegetation response to climate variability, we analyzed the seasonal precipitation, potential evapotranspiration, temperature extremes, and high-resolution normalized difference vegetation index (NDVI) data at five altitudinal floors above 2500 m. We considered the bi-monthly maximum NDVI in austral summer (NDVIx) and the difference between NDVIx and that of two months prior (NDVId) to reflect the primary productivity throughout the growing season. We observed positive linear correlations between NDVIx and winter precipitation and negative ones with autumn/winter maximum temperatures at lower altitudes (the latter likely led to the negative correlation between NDVIx and potential evapotranspiration). The NDVIx showed clear latitudinal and altitudinal variability, with the southern region exhibiting an opposite NDVIx climate correlation pattern at altitudes greater than 3500 m. The NDVId correlations were more spatially uniform and showed similar patterns to those of NDVIx at lower altitudes. Precipitation declined at a rate of −45%/decade, which contributed to the −1.5%/decade and −5%/decade decline in NDVIx and NDVId, respectively. The positive NDVIx trends (1.5%/decade) above 3500 m in the southern region led to an early snowpack retreat, which was consistent with the temporal increase in autumn maximum temperature of 1.23 °C/decade. Our results suggest that ongoing climate change will have a negative impact on the high-altitude ecosystems of the semiarid Andes.
Geophysical Research Letters, Mar 19, 2019
Tropical perturbations have been shown theoretically and observationally to excite long-range atm... more Tropical perturbations have been shown theoretically and observationally to excite long-range atmospheric responses in the form of Rossby wave teleconnections that result from the equator to pole gradient of planetary vorticity. An extreme teleconnection event occurred during March 2015 in the Southeastern Pacific. As a result, extreme high temperatures were observed in Southwestern South America and the Antarctic Peninsula simultaneously with an extreme rainfall and flood event in the hyperarid Atacama desert. We show that the origin of these seemingly disconnected extreme events can be traced to a Rossby wave response to the strongest Madden-Julian Oscillation (MJO) on record in the tropical central Pacific. A barotropic wave number 3 to 4 perturbation with group velocity between 15 and 30 m/s is consistent with the trajectory and timing followed by the upper-level anomalies radiating away from the tropics after the MJO episode. Plain Language Summary Large atmospheric waves can travel from the tropical regions after being excited by deep convective systems over the oceans. Sometimes this tropical rainfall occurs associated to tropical waves that take from 30 to 60 days to travel around the planet, known as the Madden-Julian Oscillations. The strongest of such Madden-Julian wave was observed during March 2015. Here we show that this wave triggered a response that traveled far east and south of the original rainfall heating, producing extreme weather in Antarctica (highest temperature in continental Antarctica observed on record) as well as extreme weather in the Pacific South American coast (major flooding in the Atacama desert). We emphasize that this case illustrates the importance of tropical extremes in setting temperature and precipitation extremes far away from the tropics, including polar regions. This has major consequences for these extreme environments: for the maintenance of the ice shelves in Antarctic Peninsula and for the hyperarid character of the Atacama desert. the highest temperatures ever recorded for continental Antarctica (Skansi et al., 2017) (17.5 • C on 24 March 2015, see Figure S1b). This extreme Antarctic heat wave triggered a significant melting on the Larsen C ice sheet (Munneke et al., 2018) and was ultimately traced to foehn-induced warming that resulted from a RESEARCH LETTER
Remote Sensing of Environment, Mar 1, 2017
The near-shore surface mesoscale atmospheric circulation in the upwelling systems off Peru and Ch... more The near-shore surface mesoscale atmospheric circulation in the upwelling systems off Peru and Chile is influential on the Sea Surface Temperature through Ekman transport and pumping. There has been a debate whether or not the so-called "wind drop-off", that is a shoreward decrease of the surface wind speed near the coast, can act as an effective forcing of upwelling through Ekman pumping. Although the wind drop-off has been simulated by high-resolution atmospheric models, it has not been well documented due to uncertainties in the scatterometry-derived wind estimates associated with land contamination. Here we use the along-track altimetry-derived surface wind speed data from ENVISAT, Jason-1, Jason-2, and SARAL satellites, to document the spatial variability of the mean wind drop-off near the coast as estimated from the inversion of the radar backscattering coefficient. The data are first calibrated so as to fit with the scatterometer observations of previous and current satellite missions (QuikSCAT, ASCAT). The calibrated data are then analyzed near the coast and a wind drop-off scale is estimated. The results indicate that the wind drop-off takes place all along the coast, though with a significant alongshore variability in its magnitude. Differences between products are shown to be related both to the differences in repeat cycle between the different altimetry missions and to the peculiarities of the coastline shape at the coastal latitudes of the incident tracks. The relative contribution of Ekman pumping and Ekman transport to the total transport is also estimated indicating a comparable contribution off Chile while transport associated to Ekman pumping is on average~1.4 larger than Ekman transport off Peru. Despite the aliasing effect associated with the weak repetitivity of the satellite orbit and the high frequency variability of the winds in this region, the analysis suggests that the seasonal cycle of the surface winds near the coast could be resolved at least off Peru.
Boundary-Layer Meteorology, Jan 7, 2022
The World Meteorological Organization Aircraft Meteorological Data Relay (AMDAR) programme refers... more The World Meteorological Organization Aircraft Meteorological Data Relay (AMDAR) programme refers to meteorological data gathered by commercial aircraft and made available to weather services. It has become a major source of upper-air observations whose assimilation into global models has greatly improved their performance. Near busy airports, AMDAR data generate semi-continuous vertical profiles of temperature and winds, which have been utilized to produce climatologies of atmospheric-boundary-layer (ABL) heights and general characterizations of specific cases. We analyze 2017-2019 AMDAR data for Santiago airport, located in the centre of a 40 × 100 km 2 subtropical semi-arid valley in central Chile, at the foothills of the Andes. Profiles derived from AMDAR data are characterized and validated against occasional radiosondes launched in the valley and compared with routine operational radiosondes and with reanalysis data. The cold-season climatology of AMDAR temperatures reveals a deep nocturnal inversion reaching up to 700 m above ground level (a.g.l.) and daytime warming extending up to 1000 m a.g.l. Convective-boundary-layer (CBL) heights are estimated based on AMDAR profiles and the daytime heat budget of the CBL is assessed. The CBL warming variability is well explained by the surface sensible heat flux estimated with sonic anemometer measurements at one site, provided advection of the cool coastal ABL existing to the west is included. However, the CBL warming accounts for just half of the mean daytime warming of the lower troposphere, suggesting that rather intense climatological diurnal subsidence affects the dynamics of the daytime valley ABL. Possible sources of this subsidence are discussed.
World water resources, Dec 4, 2020
Journal of Arid Environments
Remote Sensing of Environment, 2017
World Seas: an Environmental Evaluation, 2019
The coast of mainland Chile extends from 18°S to about 56°S, is about 4200 km long (Fig. 29.1), a... more The coast of mainland Chile extends from 18°S to about 56°S, is about 4200 km long (Fig. 29.1), and contains a highly heterogeneous coastal geomorphology, climate, and oceanographic features. Two main tectonic plates configure the large-scale geomorphology of the coastline, namely the oceanic "Nazca" plate and the continental plate of South America, and direct collision and subduction results in a very narrow continental shelf and a deep trench along the coast (see Fig. 29.1). These, in combination with geological hotspots, are also responsible for the creation of seamount chains (Cahill & Isacks, 1992). The northern Chilean coastline between 18°S and 40°S is a continuous, relatively straight wave-exposed shore, while between 40°S and 56°S it is fragmented with long fjords and small archipelagos with extensive wave-protected zones. The eastward flowing West Wind Drift reaches the South American continent between 40°S and 45°S, resulting in a northwardflowing branch, the Humboldt Current System (HCS), and a southward-flowing branch, the Magellan Current (Strub, Mesías, Montecino, Rutllant, & Salinas, 1998) (see Fig. 29.1). The complex system of currents within the larger HCS determines diverse and productive coastal ecosystems and biogeographic zones along the mainland coast of Chile (Camus, 2001; Thiel et al., 2007). 29.2 GEOLOGICAL DESCRIPTION From 18°S to 23°S the coast is mainly Jurassic and Cretaceous, with sedimentary intrusions (Araya-Vergara, 1981). The few small rivers (e.g., "El Loa" river) add sediments and freshwater to the coast especially during the rainy season in the Andes (December-January). Between 24°S and 33°S, the coast is primarily granitic with lower elevation and some extended terraces. Continuous rocky reefs are interrupted by sandy beaches, boulder fields, and estuaries, which tend to become more common toward the south (Santelices, 1991). The southern-central coast of Chile, from 33°S to 41°S, is mainly of Precambrian metamorphic shales with extended coastal terraces. This part is influenced by persistent river inflow. This coastline has diverse coastal habitats, grading, in general terms, from extended rocky platforms in the north to large sandy beaches and coastal wetlands which are more frequent to the south. To the south of Chiloé island (41°S), the coast has erosional tectonic patterns of fjords and a glaciated interior (Araya-Vergara, 1981). A large number of islands generate many wave-protected bays and fjords. The continental shelf is relatively narrow in the north and expands toward the south. Deep canyons extend from the river basins, many of them associated with methane seeps between about 33°S and 36°S and there are also extensive fields of methane hydrates (Sellanes, Quiroga, & Neira, 2008). The Atacama Trench is very deep in the north (~ 7000 m) and becomes shallower to the south (Stuut, Kasten, Lamy, & Hebbeln, 2007). Chapter 29 674 World Seas: An Environmental Evaluation FIG. 29.1 Map of Chile, with principal currents and main geographic features of the Chilean continental coast.
Journal of Geophysical Research: Oceans, 2019
In Eastern Boundary Upwelling Systems (EBUS), the upwelling favorable wind speeds decrease toward... more In Eastern Boundary Upwelling Systems (EBUS), the upwelling favorable wind speeds decrease toward the coast in the so‐called wind drop‐off coastal strip, which has been shown to be influential on the coastal upwelling dynamics, particularly in terms of the relative contributions of Ekman drift and Ekman suction to coastal upwelling. Currently, the wind drop‐off length scale is not properly resolved by the atmospheric forcing of regional ocean models in EBUS, featuring a smoother cross‐shore wind profile that results in stronger near‐shore speeds that could partly explain the coastal cold bias often found in those model simulations. Here, as a case study for the upwelling system off Central Chile, the sensitivity of upwelling dynamics to the coastal wind reduction is investigated using a Regional Ocean Modeling System (ROMS). Coastal wind profiles at different resolutions are first generated using a regional atmospheric model, validated from altimeter data, and then used to correct t...
Atmospheric Environment, 2017
Dust storms that develop along the Pisco-Ica desert in Southern Peru, locally known as "Paracas" ... more Dust storms that develop along the Pisco-Ica desert in Southern Peru, locally known as "Paracas" winds have ecological, health and economic repercussions. Here we identify dust sources through MODIS (Moderate Resolution Imaging Spectroradiometer) imagery and analyze HYSPLIT (Hybrid Single Particles Lagrangian Integrated Trajectory) model trajectories and dispersion patterns, along with concomitant synoptic-scale meteorological conditions from National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis (NCEP/NCAR). Additionally, surface pressure data from the hourly METeorological Aerodrome Report (METAR) at Arica (18.5°S, 70.3°W) and Pisco (13.7°S, 76.2°W) were used to calculate Alongshore (sea-level) Pressure Gradient (APG) anomalies during Paracas dust storms, their duration and associated wind-speeds and wind directions. This study provides a review on the occurrence and strength of the Paracas dust storms as reported in the Pisco airfield for five-year period and their correspondence with MODIS true-color imagery in terms of dustemission source areas. Our results show that most of the particle fluxes moving into the Ica-Pisco desert area during Paracas wind events originate over the coastal zone, where strong winds forced by steep APGs develop as the axis of a deep mid-troposphere trough sets in along north-central Chile. Direct relationships between Paracas wind intensity, number of active dustemission sources and APGs are also documented, although the scarcity of simultaneous METAR/MODIS data for clearly observed MODIS dust plumes prevents any significant statistical inference. Synoptic-scale meteorological composites from NCEP/NCAR reanalysis data show that Paracas wind events (steep APGs) are mostly associated with the strengthening
Journal of Climate, 2016
The climatology and recent trends of low-level coastal clouds at three sites along the northern C... more The climatology and recent trends of low-level coastal clouds at three sites along the northern Chilean coast (18.3°–23.4°S) are documented based upon up to 45 years of hourly observations of cloud type, coverage, and heights. Consistent with the subtropical location, cloud types are dominated by stratocumuli having greatest coverage (>7 oktas) and smaller heights (600–750 m) during the nighttime of austral winter and spring. Meridionally, nighttime cloud fraction and cloud-base heights increase from south to north. Long-term trends in mean cloud cover are observed at all sites albeit with a seasonal modulation, with increasing (decreasing) coverage in the spring (fall). Consistent trend patterns are also observed in independent sunshine hour measurements at the same sites. Cloud heights show negative trends of about 100 m decade−1 (1995–2010), although the onset time of this tendency differs between sites. The positive cloud fraction trends during the cloudy season reported here...
Ambiente y …, 1989
RESUMEN. La tierra enfrenta un cambio climático derivado de la actividad del hombre. Este cambio ... more RESUMEN. La tierra enfrenta un cambio climático derivado de la actividad del hombre. Este cambio excede en magnitud y rapidez a las variaciones ocurridas en los últimos 10.000 años y plantea problemas importantes de adaptación y planificación. Con la escasa ...
Journal of Applied Meteorology and Climatology, 2016
Theterral de Vicuñais a warm and dry wind that flows down the Elqui Valley in north-central Chile... more Theterral de Vicuñais a warm and dry wind that flows down the Elqui Valley in north-central Chile typically at dawn and early morning. Given that most terral episodes occur in austral winter when chill accumulation by deciduous fruit trees proceeds, negative effects on agriculture may be expected. During 11 (2004–14) winters a meteorological characterization of terral winds and the assessment of their impact on chill accumulation, by the modified Utah Model and the Dynamic Model, were performed. Within this period, 67 terral days (TD) were identified as those in which nighttime to early morning wind direction and speed, air temperature, and relative humidity reached defined thresholds on an hourly basis (terral hours). Most frequent TD featured 6–9 consecutive terral hours; duration is considered here as a proxy for their intensity. Synoptic-scale meteorological analysis shows that 65% of moderate and strong terral events develop as a cold, migratory anticyclone drifts poleward of t...
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Papers by Jose A Rutllant