•Detailed satellite description of winds and ocean circulation off southern Chile.•Seasonal winds and current reversals; unexpected equatorward flow.•Strong oceanic connections to tropical Pacific ...ENSO variability.•2015–2016 ENSO conditions favored A. catenella bloom north of Chiloé Island.•The strongest atmospheric blocking in 39 years; plays a role in the bloom.
Satellite and atmospheric model fields are used to describe the wind forcing, surface ocean circulation, temperature and chlorophyll-a pigment concentrations along the coast of southern Chile in the transition region between 38° and 46°S. Located inshore of the bifurcation of the eastward South Pacific Current into the equatorward Humboldt and the poleward Cape Horn Currents, the region also includes the Chiloé Inner Sea and the northern extent of the complex system of fjords, islands and canals that stretch south from near 42°S. The high resolution satellite data reveal that equatorward currents next to the coast extend as far south as 48°–51°S in spring-summer. They also display detailed distributions of forcing from wind stress and wind stress curl near the coast and within the Inner Sea. Between 38°–46°S, both winds and surface currents during 1993–2016 change directions seasonally from equatorward during summer upwelling to poleward during winter downwelling, with cooler SST and greater surface chlorophyll-a concentrations next to the coast during upwelling, opposite conditions during downwelling. Over interannual time scales during 1993–2016, there is a strong correlation between equatorial El Niño events and sea level and a moderate correlation with alongshore currents. Looking more closely at the 2014–2016 period, we find a marginal El Niño during 2014 and a strong El Niño during 2015 that connect the region to the tropics through the oceanic pathway, with some atmospheric connections through the phenomenon of atmospheric blocking (as noted by others). The period also includes a Harmful Algal Bloom of the dinoflagellate Alexandrium catenella during early-2016 that occurred during a sequence of physical conditions (winds, currents and temperatures) that would favor such a bloom. The most anomalous physical condition during this specific bloom is an extreme case of atmospheric blocking that creates a long period of calm in austral autumn after strong upwelling in austral summer. The blocking is related to the 2015–2016 El Niño and an unusual coincident positive phase of the Southern Annular Mode.
ABSTRACT
The climatology of wind waves over the Southeast Pacific is analysed using a 32‐year hindcast from the WaveWatch III model, complemented by satellite‐derived significant wave height (SWH) ...and buoy measurements for validation. Using partitioned spectral data, a regional climatology of wind sea and swell parameters was constructed. In general, the simulated SWH shows a good agreement with satellite and in situ SWH measurements, although the model appears to have a spatially uniform bias of approximately 0.3 m. The spatial pattern of SWH is clearly influenced by the meridional variation of mean surface wind speed, where the stronger winds over the Southern Ocean play a significant role generating higher waves at higher latitudes. Nevertheless, regional features are observed in the annual variability of SWH, which are associated with the existence of atmospheric coastal low‐level jets off the coast of Peru and central Chile. In particular, the seasonal variation of these synoptic scale jets shows a direct relationship with the annual variability of SWH and with the probability of occurrence of wind sea conditions. Off the coast of Peru at approximately 15°S the coastal low‐level jet is strongest during austral winter, increasing the wind sea SWH. In contrast, off central Chile, there is an important increase of wind sea SWH during summer. The seasonal variation of the wind sea component leads to a contrasting seasonal variation of the total SWH at these locations: off Peru the coastal jet amplifies the annual variability of SWH, while off Central Chile the annual variability of SWH is suppressed by the presence of the coastal jet. Although the general conclusions of this research are considered to be robust, we discuss the limitations of the spectral partitioning method used to distinguish wind sea and swell‐sea states.
Carbon system parameters measured during several expeditions along the coast of Chile (23°S–56°S) have been used to show the main spatial and temporal trends of air‐sea CO2 fluxes in the coastal ...waters of the eastern South Pacific. Chilean coastal waters are characterized by strong pCO2 gradients between the atmosphere and the surface water, with high spatial and temporal variability. On average, the direction of the carbon flux changes from CO2 outgassing at the coastal upwelling region to CO2 sequestering at the nonupwelling fjord region in Chilean Patagonia. Estimations of surface water pCO2 along the Patagonian fjord region showed that, while minimum pCO2 levels (strong CO2 undersaturation) occurs during the spring and summer period, maximum levels (including CO2 supersaturation) occur during the austral winter. CO2 uptake in the Patagonia fjord region during spring‐summer is within the order of −5 mol C m−2 yr−1, indicating a significant regional sink of atmospheric CO2 during that season. We suggest that the CO2 sink at Patagonia most probably exceeds the CO2 source exerted by the coastal upwelling system off central northern Chile.
Key Points
Strong CO2 outgassing at the coastal upwelling of Chile
Strong CO2 uptake at the fjord region of Chile
Freshwater inputs to the Pacific Patagonia coastal ocean enhance CO2 uptake
The climatology and recent trends of low-level coastal clouds at three sites along the northern Chilean coast (18.3°–23.4Skillful seasonal forecasting of tropical cyclone (TC; wind speed $17.5ms21) ...activity is challenging, even more so when the focus is on major hurricanes (wind speed $49.4ms21), the most intense hurricanes (category 4 and 5; wind speed $58.1ms–1), and landfalling TCs. This study shows that a 25-km-resolution global climate model High-Resolution Forecast-Oriented Low Ocean Resolution (FLOR) model (HiFLOR) developed at the Geophysical Fluid Dynamics Laboratory (GFDL) has improved skill in predicting the frequencies of major hurricanes and category 4 and 5 hurricanes in the North Atlantic as well as landfalling TCs over the United States and Caribbean islands a few months in advance, relative to its 50-km-resolution predecessor climate model (FLOR). HiFLOR also shows significant skill in predicting category 4 and 5 hurricanes in the western North Pacific and eastern North Pacific, while both models show comparable skills in predicting basin-total and landfalling TC frequency in the basins. The improved skillful forecasts of basintotal TCs, major hurricanes, and category 4 and 5 hurricane activity in the North Atlantic by HiFLOR are obtained mainly by improved representation of the TCs and their response to climate from the increased horizontal resolution rather than by improvements in large-scale parameters.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 disagree with previous studies, with discrepancies attributed to differences in datasets used or to methodological differences in data analysis. The cloud-base height tendency, together with a less rapid lowering of the subsidence inversion base height, suggests a deepening of the coastal cloud layer. While consistent with the tendency toward greater low-level cloud cover and the known cooling of the marine boundary layer in this region, these tendencies are at odds with a drying trend of the near-surface air documented here as well. Assessing whether this intriguing result is caused by physical factors or by limitations of the data demands more detailed observations, some of which are currently under way.
Black carbon transport from the Santiago Metropolitan Area, Chile, up to the adjacent Andes Cordillera and its glaciers is of major concern. Its deposition accelerates the melting of the snowpack, ...which could lead to stress on water supply in addition to climate feedback. A proposed pathway for this transport is the channelling through the network of canyons that connect the urban basin to the elevated summits, as suggested by modelling studies, although no observations have validated this hypothesis so far. In this work, atmospheric measurements from a dedicated field campaign conducted in winter 2015, under severe urban pollution conditions, in Santiago and the Maipo canyon, southeast of Santiago, are analysed. Wind (speed and direction) and particulate matter concentrations measured at the surface and along vertical profiles, demonstrate intrusions of thick layers (up to 600 m above ground) of urban black carbon deep into the canyon on several occasions. Transport of PM down-valley occurs mostly through shallow layers at the surface except in connection with deep valley intrusions, when a secondary layer in altitude with return flow (down-valley) at night is observed. The transported particulate matter is mostly from the vicinity of the entrance to the canyon and uncorrelated to concentrations observed in downtown Santiago. Reanalyses data show that for 10% of the wintertime days, deep intrusions into the Maipo canyon are prevented by easterly winds advecting air pollutants away from the Andes. Also, in 23% of the cases, intrusions proceed towards a secondary north-eastward branch of the Maipo canyon, leaving 67% of the cases with favourable conditions for deep penetrations into the main Maipo canyon. Reanalyses show that the wind directions associated to the 33% anomalous cases are related to thick cloud cover and/or the development of coastal lows.
•Transport of urban BC in deep, dense layers is found far into an Andean canyon.•A return flow in an elevated secondary layer is observed with valley intrusions.•Air pollutants transported into the canyon are from the vicinity of its entrance.•Climatologically, intrusions into the canyon occur 90% of the wintertime days.•Cloud cover prevents air masses flow towards the Andes 10% of winter days.
The purpose of the present study is to explore the synoptic-scale atmospheric circulation and water vapor transport that contribute to triggering landslides in the mid-Elqui basin (30°S, 70.5°W) ...since the early 20th century. A total of 12 storms during the modern period (1957–2017) were identified from various sources and analyzed using ERA5 Reanalysis data. An additional set of eight storms was included and characterized using 20th Century Reanalysis data. The results reveal that high-amplitude, deep troughs extending into the subtropics off the west coast of South America are ubiquitous in these storms. Maximum integrated water vapor transport from the northwest (NW) or west-northwest (WNW) was observed on the coast (25–30°S), with values sometimes exceeding 300 kg s-1 m-1, often reaching more than five standard deviations above the mean. Atmospheric rivers near the study region were found to be involved in all 12 modern landslide-producing storms. Moreover, most storms occur during the warm phase of the El Niño–Southern Oscillation (ENSO) and/or phases 7–8–1 of the Madden–Julian Oscillation (MJO). Backward-trajectory analyses indicate that in all but one of the modern storms, water vapor transport originated in the Central Tropical Pacific, where ocean warming characterizes the convective phases of ENSO and/or MJO.
•Landslides in northern Chile are tied to cyclonic perturbations and atmospheric rivers.•Long-range water vapor transport is crucial, reaching 5 std. Deviations above mean at 30°S.•Landslide storms linked to warm ENSO phase and MJO phases 7–8–1, driven by teleconnections.
The meteorological factors of the severe wintertime particulate matter (PM) air pollution problem of the city of Santiago, Chile, are investigated with newly available observations, including a 30 m ...tower measuring near-surface stability, winds and turbulence, as well as lower-tropospheric vertical profiles of temperature and winds measured by commercial airplanes operating from the Santiago airport (AMDAR database). Focusing on the cold season of the years 2017–2019, high-PM days are defined using an index of evening concentrations measured in the western part of the city. The diurnal cycles of the different meteorological variables computed over 25 PM episodes are compared against the overall diurnal cycles. PM episodes are associated with enhanced surface stability and weaker surface winds and turbulence during the evening and night. AMDAR vertical profiles of temperature and winds during episodes reveal a substantial lower-tropospheric warming attributed to enhanced regional subsidence, which is consistent with the shallower daytime boundary layer depth and the increased surface thermal amplitude observed during these days. An explanation for the weak surface winds during PM episodes was not evident, considering that these are clear days that would strengthen the local valley wind system. Two possible mechanisms are put forward to resolve this issue, which can be tested in the future using high-resolution numerical modeling validated with the new data described here.
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
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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.
Surface winds along the subtropical west coast of South America are characterized by the quasi-weekly occurrences of low-level jet events. These short lived but intense wind events impact the coastal ...ocean environment. Hence, identifying long-term trends in the coastal low-level jet (CLLJ) is essential for understanding changes in marine ecosystems. Here we use ERA5 reanalysis (1979–2019) and an objective algorithm to track anticyclones to investigate recent changes in CLLJ events off central Chile (25–43 °S). Results present evidence that the number of days with intense wind (≥10 ms−1), and the number and duration of CLLJ events have significantly changed off central Chile in recent decades. There is an increase in the number of CLLJ events in the whole study area during winter (June-July-August; JJA), while during summer (December–January–February; DJF) a decrease is observed at lower latitudes (29–34 °S), and an increase is found at the southern boundary of the Humboldt system. We suggest that changes in the central pressures and frequency of extratropical, migratory anticyclones that reach the coast of South America, which force CLLJs, have played an important role in the recent CLLJ changes observed in this region.
Abstract
Biological productivity in the ocean along the Chilean coast is tied to upwelling that is primarily forced by equatorward wind stress and wind stress curl on the ocean surface. Southerly ...alongshore flow is driven by the southeast Pacific (SEP) anticyclone, and its intensity and position vary on a range of time scales. Variability of the SEP anticyclone has been linked to large-scale circulations such as El Niño–Southern Oscillation and the Madden–Julian oscillation. The actual timing, duration, and nature of the seasonal meridional drift of the SEP anticyclone are associated with the onset, demise, and strength of the local upwelling season. Seasonal variation is especially marked at the Punta Lavapié (37°S) upwelling focus, where there is a clear upwelling season associated with a change of the cumulative upwelling index (CUI) slope between positive and negative. The Punta Lengua de Vaca (30°S) focus typically exhibits upwelling year-round and has less distinct transitions, making it more difficult to identify an enhanced upwelling season. A two-phase linear regression model, which is typically used to detect subtle climate changes, is applied here to detect seasonal changes in CUI at Punta Lengua de Vaca. This method objectively finds distinct transitions for most years. The spring-to-summer transition is more readily detected and the slackening of the upwelling-favorable winds, warmer waters, and longer wind strengthening–relaxation cycles change the coastal upwelling ecosystem. While the spring-to-summer transition at Punta Lengua de Vaca could be influenced by large-scale circulations, the actual dates of transition are highly variable and do not show a clear relationship.
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