Local winds

We investigate the seasonal variability of the southern tip (30°-38°S) of the eastern South Pacific oxygen minimum zone (OMZ) based on a high horizontal resolution (1/12°) regional coupled physical-biogeochemical model simulation. The simulation is validated by available in situ observations and the OMZ seasonal variability is documented. The model OMZ, bounded by the contour of 45 μM, occupies a large volume (4.5x10 4 km 3) during the beginning of austral winter and a minimum (3.5x10 4 km 3) at the end of spring, just 1 and 2 months after the southward transport of the Peru-Chile Undercurrent (PCUC) is maximum and minimum, respectively. We showed that the PCUC significantly impacts the alongshore advection of dissolved oxygen (DO) modulating the OMZ seasonal variability. However, zonal transport of DO by meridionally alternating zonal jets and mesoscale eddy fluxes play also a major role in the seasonal and spatial variability of the OMZ. Consistently, a DO budget analysis reveals a significant contribution of advection terms to the rate of change of DO and the prominence of mesoscale variability within the seasonal cycle of these terms. Biogeochemical processes and horizontal and vertical mixing, associated with subgrid scale processes, play only a secondary role in the OMZ seasonal cycle. Overall, our study illustrates the interplay of mean and (mesoscale) eddy-induced transports of DO in shaping the OMZ and its seasonal cycle off Central Chile. Plain Language Summary Dissolved oxygen in the ocean strongly impacts most marine ecosystems. Its distribution depends mainly on physical and biogeochemical processes. In the eastern South Pacific, water with very low oxygen is present at intermediate depths (100-800 m). This oxygen minimum zone (OMZ) is associated with a regional water mass called Equatorial Subsurface Water which is transported southward along the coast by the Peru-Chile Undercurrent. Here, using a physical/biogeochemical model we investigate the main mechanisms controlling the seasonal variability of the OMZ off central Chile. We found that the total volume of the low-oxygen waters is reduced by 25% during spring. This seasonal change is closely related to changes in the water mass composition and is mainly driven by changes in the undercurrent transport, but zonal currents and eddy fluxes, largely related to mesoscale variability, play also a major role in the seasonal and spatial variability of the OMZ, while biogeochemical and mixing processes play only a secondary role.

During 2014 exceptionally warm water temperatures developed across a wide area off the California coast and within San Francisco Bay (SFB) and persisted into 2016. Observations and numerical model output are used to document this warming and determine its origins. The coastal warming was mostly confined to the upper 100 m of the ocean and was manifested strongly in the two leading modes of upper ocean (0-100 m) temperature variability in the extratropical eastern Pacific. Observations suggest that the coastal warming in 2014 propagated into nearshore regions from the west while later indicating a warming influence that propagated from south to north into the region associated with the 2015-2016 El Niño event. An analysis of the upper ocean (0-100 m) heat budget in a Regional Ocean Modeling System (ROMS) simulation confirmed this scenario. The results from a set of sensitivity runs with the model in which the lateral boundary conditions varied supported the conclusions drawn from the heat budget analysis. Concerning the warming in the SFB, an examination of the observations and the heat budget in an unstructured-grid numerical model simulation suggested that the warming during the second half of 2014 and early 2016 originated in the adjacent California coastal ocean and propagated through the Golden Gate into the Bay. The finding that the coastal and Bay warming are due to the relatively slow propagation of signals from remote sources raises the possibility that such warming events may be predictable many months or even several seasons in advance. Plain Language Summary The origins of the exceptionally warm water temperatures that developed off the California coast and in San Francisco Bay were studied using observations and computer model experiments. The coastal warming was mostly confined to the upper ocean. The coastal warming in 2014 was found to have moved into coastal waters from further offshore in the northeastern Pacific. Warming persisted into 2015-2016 as a warming influence from the south associated with the 2015-16 El Niño event in the tropical Pacific Ocean. The model experiments suggested confirmed that propagation of the warming signals from the west and north into the California coastal ocean and suggested that the warming in San Francisco Bay was found to have originated primarily in the adjacent California coastal ocean. The finding that the coastal and Bay warming are due to the relatively slow propagation of signals from remote sources raises the possibility that such warming events may be predictable many months or even several seasons in advance.

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...

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...

During 2014 exceptionally warm water temperatures developed across a wide area off the California coast and within San Francisco Bay (SFB) and persisted into 2016. Observations and numerical model output are used to document this warming and determine its origins. The coastal warming was mostly confined to the upper 100 m of the ocean and was manifested strongly in the two leading modes of upper ocean (0–100 m) temperature variability in the extratropical eastern Pacific. Observations suggest that the coastal warming in 2014 propagated into nearshore regions from the west while later indicating a warming influence that propagated from south to north into the region associated with the 2015–2016 El Niño event. An analysis of the upper ocean (0–100 m) heat budget in a Regional Ocean Modeling System (ROMS) simulation confirmed this scenario. The results from a set of sensitivity runs with the model in which the lateral boundary conditions varied supported the conclusions drawn from the...

Manuscrito recibido el 9 de febrero de 2021, en su versión final el 2 de julio de 2021) RESUMEN Este artículo muestra el impacto de un eclipse en las variables meteorológicas observadas por una estación de altura bajo un contexto observacional de brisa valle-montaña en la zona del valle inferior del río Manso, Río Negro. El 14 de diciembre de 2020 la luna ocultó entre el 90 y 100 % del disco solar sobre Patagonia Norte. Al cumplirse exactamente un año de su instalación, la estación meteorológica Los Notros, ubicada en la ladera norte del cordón montañoso que acompaña al río, registró la evolución de la temperatura y humedad del aire, la velocidad y dirección del viento y la radiación global durante el eclipse. Particularmente, como la estación meteorológica fue instalada para estudiar la brisa de valle-montaña, se discute en este artículo las condiciones que permiten el desarrollo de la brisa en el valle, y el efecto que tuvo el eclipse en la circulación sobre la ladera. Palabras clave: Brisa valle-montaña, Río Negro, Los Notros.

Oxygen minimum zones (OMZs) are extended oceanic regions for which dissolved oxygen concentration is extremely low. They are suspected to be expanding in response to global warming. However, currently, the mechanisms by which OMZ varies in response to climate variability are still uncertain. Here, the variability of the subtropical OMZ off central Chile of a regional coupled physical–biogeochemical regional model simulation was analyzed for the period 2000–2008, noting that its fluctuations were significant despite the relatively weak amplitude of the El Niño/Southern Oscillation (ENSO). In particular, the interannual variability in the OMZ volume (OMZVOL, defined as the volume with dissolved oxygen concentration (DO) ≤ 45μM) was approximately 38% larger than that of the seasonal cycle, with maximum and minimum anomalies of OMZVOL taking place during two cold La Niña (LN) years (2001 and 2007). The model analyses further reveal that these anomalies resulted from a combined effect of...

We investigate the seasonal variability of the southern tip (30°-38°S) of the eastern South Pacific oxygen minimum zone (OMZ) based on a high horizontal resolution (1/12°) regional coupled physical-biogeochemical model simulation. The simulation is validated by available in situ observations and the OMZ seasonal variability is documented. The model OMZ, bounded by the contour of 45 μM, occupies a large volume (4.5x10 4 km 3) during the beginning of austral winter and a minimum (3.5x10 4 km 3) at the end of spring, just 1 and 2 months after the southward transport of the Peru-Chile Undercurrent (PCUC) is maximum and minimum, respectively. We showed that the PCUC significantly impacts the alongshore advection of dissolved oxygen (DO) modulating the OMZ seasonal variability. However, zonal transport of DO by meridionally alternating zonal jets and mesoscale eddy fluxes play also a major role in the seasonal and spatial variability of the OMZ. Consistently, a DO budget analysis reveals a significant contribution of advection terms to the rate of change of DO and the prominence of mesoscale variability within the seasonal cycle of these terms. Biogeochemical processes and horizontal and vertical mixing, associated with subgrid scale processes, play only a secondary role in the OMZ seasonal cycle. Overall, our study illustrates the interplay of mean and (mesoscale) eddy-induced transports of DO in shaping the OMZ and its seasonal cycle off Central Chile. Plain Language Summary Dissolved oxygen in the ocean strongly impacts most marine ecosystems. Its distribution depends mainly on physical and biogeochemical processes. In the eastern South Pacific, water with very low oxygen is present at intermediate depths (100-800 m). This oxygen minimum zone (OMZ) is associated with a regional water mass called Equatorial Subsurface Water which is transported southward along the coast by the Peru-Chile Undercurrent. Here, using a physical/biogeochemical model we investigate the main mechanisms controlling the seasonal variability of the OMZ off central Chile. We found that the total volume of the low-oxygen waters is reduced by 25% during spring. This seasonal change is closely related to changes in the water mass composition and is mainly driven by changes in the undercurrent transport, but zonal currents and eddy fluxes, largely related to mesoscale variability, play also a major role in the seasonal and spatial variability of the OMZ, while biogeochemical and mixing processes play only a secondary role.

This study evaluates the swimming behaviour of pre-settled fish larvae of the triplefin Helcogrammoides chil­ensis (Tripterygiidae) in relation to local environmental conditions. Larval aggregations were recorded on rocky reefs off central Chile during the austral summer of 2014 and 2016 to describe their swimming behaviour (i.e. solitary, shoaling, schooling) and relate it to in situ water temperature, wind stress, wind speed and turbulence. Shoaling and solitary behaviour were influenced only by wind-induced turbulence in 2014 and by seawater temperature and wind stress in 2016. Schooling behaviour was not influenced by any of the environmental variables. In situ swimming behaviour of fish larvae has been little investigated, and this work proposes a non-invasive in situ methodology for studying fish larval behaviour.

By numerically simulating atmospheric flow, the impact of surface friction on winds that are canalized by a mountain is investigated. The simulations show that in the case of wind that is accelerated by orography, surface friction has a significantly stronger wind-breaking effect than if mountains have not accelerated the wind. These results are particularly encouraging for plans to change the local wind climate in Iceland by massive growing of trees.

The contribution of high-frequency wind to the Peruvian upwelling system during 2014–2016 was studied using the Regional Ocean Modeling System (ROMS), forced by four different temporal resolution (six-hourly, daily, weekly, and monthly) wind forcing. A major effect of the high-frequency wind is its warming of the water at all depths along the Peruvian coast. The mechanism for the temperature changes induced by high-frequency wind forcing was analyzed through heat budget analysis, which indicated a three-layer structure. Vertical advection plays a leading role in the warming of the mixed layer (0–25 m), and enhanced vertical mixing balances the warming effect. Analysis suggests that around the depths of 25–60 m, vertical mixing warms the water by bringing heat from the surface to deeper depths. In waters deeper than 60 m, the effect of vertical mixing is negligible. The differences among the oceanic responses in the sensitivity experiments suggest that wind forcing containing variabi...

We investigate the seasonal variability of the southern tip (30°-38°S) of the eastern South Pacific oxygen minimum zone (OMZ) based on a high horizontal resolution (1/12°) regional coupled physical-biogeochemical model simulation. The simulation is validated by available in situ observations and the OMZ seasonal variability is documented. The model OMZ, bounded by the contour of 45 μM, occupies a large volume (4.5x10 4 km 3) during the beginning of austral winter and a minimum (3.5x10 4 km 3) at the end of spring, just 1 and 2 months after the southward transport of the Peru-Chile Undercurrent (PCUC) is maximum and minimum, respectively. We showed that the PCUC significantly impacts the alongshore advection of dissolved oxygen (DO) modulating the OMZ seasonal variability. However, zonal transport of DO by meridionally alternating zonal jets and mesoscale eddy fluxes play also a major role in the seasonal and spatial variability of the OMZ. Consistently, a DO budget analysis reveals a significant contribution of advection terms to the rate of change of DO and the prominence of mesoscale variability within the seasonal cycle of these terms. Biogeochemical processes and horizontal and vertical mixing, associated with subgrid scale processes, play only a secondary role in the OMZ seasonal cycle. Overall, our study illustrates the interplay of mean and (mesoscale) eddy-induced transports of DO in shaping the OMZ and its seasonal cycle off Central Chile. Plain Language Summary Dissolved oxygen in the ocean strongly impacts most marine ecosystems. Its distribution depends mainly on physical and biogeochemical processes. In the eastern South Pacific, water with very low oxygen is present at intermediate depths (100-800 m). This oxygen minimum zone (OMZ) is associated with a regional water mass called Equatorial Subsurface Water which is transported southward along the coast by the Peru-Chile Undercurrent. Here, using a physical/biogeochemical model we investigate the main mechanisms controlling the seasonal variability of the OMZ off central Chile. We found that the total volume of the low-oxygen waters is reduced by 25% during spring. This seasonal change is closely related to changes in the water mass composition and is mainly driven by changes in the undercurrent transport, but zonal currents and eddy fluxes, largely related to mesoscale variability, play also a major role in the seasonal and spatial variability of the OMZ, while biogeochemical and mixing processes play only a secondary role.

The spatial and temporal variability of nearshore winds in eastern boundary current systems affect the oceanic heat balance that drives sea surface temperature changes. In this study, regional atmospheric and oceanic simulations are used to document such processes during an atmospheric coastal jet event off central Chile. The event is well reproduced by the atmospheric model and is associated with the migration of an anomalous anticyclone in the southeastern Pacific region during October 2000. A robust feature of the simulation is a sharp coastal wind dropoff, which is insensitive to model resolution. As expected, the simulated oceanic response is a significant sea surface cooling. A surface heat budget analysis shows that vertical mixing is a major contributor to the cooling tendency both in the jet core area and in the nearshore zone where the magnitude of this term is comparable to the magnitude of vertical advection. Sensitivity experiments show that the oceanic response in the coastal area is sensitive to wind dropoff representation. This is because total upwelling, i.e., the sum of coastal upwelling and Ekman pumping, depends on the scale of wind dropoff. Because the latter is much larger than the upwelling scale, coastal wind dropoff has only a weak positive effect on vertical velocities driven by Ekman pumping but has a strong negative effect on coastal upwelling. Interestingly though, the weakening of coastal winds in the dropoff zone has a larger effect on vertical mixing than on vertical advection, with both effects contributing to a reduction of cooling.

The hypothesis that the poleward propagation of El Niño events along the coast of South America is due to Kelvin waves lacks stringent confirmation by observation. Observations are discussed which refute the Kelvin wave model. An alternative concept of poleward propagating shock waves is proposed. Some of its basic features and advantages are discussed.

During the CINDY/DYNAMO field campaign (fall/winter 2011), intensive measurements of the upper ocean, including an array of several surface moorings and ship observations for the area around 75°E-80°E, Equator-10°S, were conducted. In this study, large-scale upper ocean variations surrounding the intensive array during the field campaign are described based on the analysis of satellite-derived data. Surface currents, sea surface height (SSH), sea surface salinity (SSS), surface winds and sea surface temperature (SST) during the CINDY/DYNAMO field campaign derived from satellite observations are analyzed. During the intensive observation period, three active episodes of large-scale convection associated with the Madden-Julian Oscillation (MJO) propagated eastward across the tropical Indian Ocean. Surface westerly winds near the equator were particularly strong during the events in late November and late December, exceeding 10 m/s. These westerlies generated strong eastward jets (>1 m/s) on the equator. Significant remote ocean responses to the equatorial westerlies were observed in both Northern and Southern Hemispheres in the central and eastern Indian Oceans. The anomalous SSH associated with strong eastward jets propagated eastward as an equatorial Kelvin wave and generated OPEN ACCESS Remote Sens. 2013, 5 2073 intense downwelling near the eastern boundary. The anomalous positive SSH then partly propagated westward around 4°S as a reflected equatorial Rossby wave, and it significantly influenced the upper ocean structure in the Seychelles-Chagos thermocline ridge about two months after the last MJO event during the field campaign. For the first time, it is demonstrated that subseasonal SSS variations in the central Indian Ocean can be monitored by Aquarius measurements based on the comparison with in situ observations at three locations. Subseasonal SSS variability in the central Indian Ocean observed by RAMA buoys is explained by large-scale water exchanges between the Arabian Sea and Bay of Bengal through the zonal current variation near the equator.

Al analizar los procesos atmosféricos en la escala nacional es conveniente tener en cuenta que estos se desarrollan dentro del comportamiento de la atmósfera global; por lo tanto, es necesario comprender este último para explicar mejor los fenómenos atmosféricos nacionales. Colombia, por encontrarse geográficamente ubicada entre el Trópico de Cáncer y el Trópico de Capricornio, está sometida a los vientos alisios que soplan del noreste en el hemisferio norte y del sureste en el hemisferio sur, aunque en el país no tienen siempre exactamente estas direcciones. (Ver Fig. 1). En nuestro país, por estar en las proximidades del ecuador, la fuerza de Coriolis, que es muy importante en el campo del viento, se hace muy pequeña, y por ello los vientos están influenciados fuertemente por las condiciones locales y por el rozamiento proporcionado por las grandes irregularidades que presenta la cordillera de Los Andes al ramificarse en tres sistemas que se extienden longitudinalmente a lo largo del país con diferentes elevaciones. Además, los dos mares bañan el territorio nacional también tienen su papel en el comportamiento del viento. Esto hace que la dirección y la velocidad del viento varíen de un instante a otro y de un sitio a otro. Las diferencias en estos comportamientos climáticos en buen grado pueden explicarse con base en el desplazamiento de la Zona de Confluencia Intertropical-ZCIT a lo largo del año. En la zona de encuentro de los alisios, el desplazamiento del aire se hace más lento mientras que a mayores distancias de esa área el movimiento se hace más veloz. La latitud determina la variación a lo largo del año y los patrones de circulación atmosférica dominantes. De esa forma, en julio y agosto cuando la ZCIT se encuentra en su posición extrema al norte del país, los vientos en buena parte en esos sectores tendrán menores velocidades que en otras épocas del año. Así podemos explicarnos que en gran parte de la región Atlántica los vientos se intensifiquen durante los primeros meses del año, cuando la ZCIT se encuentra justamente al sur del país. Por el contrario, entre julio y agosto, en muchos lugares más al sur se aceleran, especialmente al oriente de la región Andina, donde las condiciones fisiográficas contribuyen a que los vientos sean más sostenidos y de mayor intensidad.

RESUMEN En este trabajo se describen las variaciones horarias medias de la dirección y velocidad del viento en las estaciones meteorológicas sinópticas de Maracaibo, Mene Grande, Coro, Puerto Cabello, Maiquetía y Barcelona. Se utilizaron los datos del período 1971-1980, tomados de la forma 0027 del Servicio de Meteorología FAV; se calcularon los valores medios horarios de velocidad y las respectivas direcciones prevalecientes; los valores obtenidos se presentan en formas de curvas diarias. Se interpretan los regímenes diarios del viento con base en los modelos teóricos de las brisas de mar-tierra y de valle-montaña. Se destaca para cada estación el papel modificador de las condiciones topográficas. Se identificaron sistemas bien organizados de vientos periódicos locales en las estaciones de Mene Grande, Maiquetía y Barcelona. ABSTRACT The diurnal variations of wind-speed and wind-direction are described

1] Coastal sea level, current, satellite altimeter data and an equatorial Kelvin wave model are used to study the dynamics of seasonal and interannual fluctuations of the Peru-Chile Undercurrent. Satellite altimetry shows that low frequency, sea level anomalies near 30°S propagate offshore as expected from Rossby wave theory. Those anomalies are related to disturbances of equatorial origin observed near the coast of South America. With a wind-forced equatorial Kelvin wave model and simple Rossby wave dynamics we show that much of the sea level anomalies, and more than 50% of the observed undercurrent variability near 30°S, at seasonal and interannual periods can be explained by long Rossby waves forced by the equatorial Kelvin waves. The amplitude of the equatorial Kelvin wave can be used to estimate the amplitude of the Rossby wave near the South American coast, and thus, to monitor low frequency changes in the Peru-Chile Undercurrent.

Coastal sea level, current, satellite altimeter data and an equatorial Kelvin wave model are used to study the dynamics of seasonal and interannual fluctuations of the Peru-Chile Undercurrent. Satellite altimetry shows that low frequency, sea level anomalies near 30°S propagate offshore as expected from Rossby wave theory. Those anomalies are related to disturbances of equatorial origin observed near the coast of South America. With a wind-forced equatorial Kelvin wave model and simple Rossby wave dynamics we show that much of the sea level anomalies, and more than 50% of the observed undercurrent variability near 30ºS, at seasonal and interannual periods can be explained by long Rossby waves forced by the equatorial Kelvin waves. The amplitude of the equatorial Kelvin wave can be used to estimate the amplitude of the Rossby wave near the South American coast, and thus, to monitor low frequency changes in the Peru-Chile Undercurrent.

The Sea Surface Temperature (SST) intraseasonal variability (40–90 days) along the coast of Peru is commonly attributed to the efficient oceanic connection with the equatorial variability. Here we investigate the respective roles of local and remote equatorial forcing on the intraseasonal SST variability off central Peru (8°S–16°S) during the 2000–2008 period, based on the experimentation with a regional ocean model. We conduct model experiments with different open lateral boundary conditions and/or sur-
face atmospheric forcing (i.e., climatological or not). Despite evidence of clear propagations of coastal trapped waves of equatorial origin and the comparable marked seasonal cycle in intraseasonal Kelvin wave
activity and coastal SST variability (i.e., peak in Austral summer), this remote equatorial forcing only accounts for $20% of the intraseasonal SST regime, which instead is mainly forced by the local winds and heat fluxes. A heat budget analysis further reveals that during the Austral summer, despite the weak along-shore upwelling (downwelling) favorable wind stress anomalies, significant cool (warm) SST anomalies along the coast are to a large extent driven by Ekman-induced advection. This is shown to be due to the shallow mixed layer that increases the efficiency by which wind stress anomalies relates to SST through advection. Diabatic processes also contribute to the SST intraseasonal regime, which tends to shorten the lag between peak SST and wind stress anomalies compared to what is predicted from an advective mixed-layer model.