Principales forzantes de las olas de calor marinas en el Pacífico Sur Oriental.
Date
2023
Authors
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Journal ISSN
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Publisher
Universidad de Concepción
Abstract
Los eventos oceanográficos extremos como las Olas de Calor Marinas (OCMs) han despertado gran interés tanto en la comunidad científica como en la sociedad en general. Este interés surge por la diversidad de impactos que ellas han generado en las distintas cuencas oceánicas y por sus severas consecuencias socioeconómicas. Los impactos de las OCMs podrían ser aún más severos y variados en el futuro ya que se proyecta un aumento en su frecuencia, duración, intensidad y extensión espacial a causa del calentamiento global. En el presente estudio se caracterizan las OCMs en el Pacífico Sur Oriental (PSO) y se examinan los mecanismos que las fuerzan y modulan. Para este fin se utilizaron datos del reanálisis global GLORYS2 y datos atmosféricos de ERA-Interim. Los resultados muestran que las OCMs en el PSO se caracterizan por intensidades promedios de ~1.2 °𝐶 e intensidades máximas que pueden alcanzar ~3 °𝐶, ambos valores por sobre la climatología del periodo de estudio (1982-2018). Estas OCMs presentaron extensiones espaciales típicas entre 103 y 104 𝑘𝑚2 y duraciones que en promedio superan un mes. Durante los eventos ENOS el impacto de las OCMs alcanza sus mayores intensidades, sus extensiones espaciales abarcan gran parte del PSO y sus duraciones son tan grandes como la presencia de los mismos eventos ENOS. Para cuantificar los forzantes de las diferentes OCM se realizó un balance de calor en la capa de mezcla y se identificaron los principales mecanismos que fuerzan y modulan las OCMs en el PSO. En específico, se estudiaron 3 regiones frente a Chile: norte (18-26°S), centro (26-39°S) y sur (39-50°S) cuyas regiones se extienden zonalmente desde la costa hasta 4° de longitud hacia el oeste. En la región norte la mayoría de las OCMs se forman principalmente por una disminución de la pérdida de calor latente desde el océano a la atmósfera, y en segundo lugar, por un aumento de la radiación térmica y calor sensible hacia el océano. Asimismo, en la región central la reducción de la evaporación también jugó un papel dominante en la generación de la mayoría de OCMs, aunque aquí este proceso se combina con un considerable aumento de la radiación solar hacia el océano durante los eventos de OCMs. En la región sur se observó que la mayoría de OCMs se generan por advección oceánica de calor, la cual es dominada por anomalías en las corrientes hacia el suroeste y un gradiente medio de temperatura en esa misma dirección. En la región sur, el único proceso atmosférico que presenta un claro aporte a la generación de calor es la reducción de la evaporación, aunque con una importancia relativamente menor comparada con la advección. Por otro lado, la advección de calor también juega un papel importante en las regiones norte y centro, presentando un patrón principalmente meridional cerca de la costa en la región norte y zonal frente al centro de Chile, encontrándose que este mecanismo se puede combinar con el intercambio de calor aire – mar anteriormente mencionado para producir OCMs de características extremas. En las tres regiones el entrainment mostró una relevancia bastante inferior a la de los otros mecanismos mencionados anteriormente durante los periodos y regiones afectadas por OCMs.
Extreme events such as Marine Heat Waves (MHWs) generate great interest both in the scientific community and in society in general. This interest arises mainly from the diverse negative impacts that MHWs have generated in all ocean basins, which produce severe socioeconomic consequences. These impacts could be even more severe and varied in future climate scenarios, with projected increases in the frequency, duration, intensity and spatial extent of MHWs due to the global warming expected by the end of the 21st century. MHWs in the Eastern South Pacific (ESP) have been less analyzed than in other regions of such ocean, so that several research initiatives in recent years (including the present work) tackle this gap. This study focuses on characterizing MHWs in the ESP and exploring the mechanisms that drive and modulate them, using the GLORYS2 and ERA-Interim global reanalysis. MHWs in the ESP are characterized by typical areas the order of 103 − 104 𝑘𝑚2 , mean area-averaged intensity anomalies of ~1.2°𝐶 and maximum anomalies reaching ~3°𝐶, and durations that exceed one month on average. Related to the driving mechanisms of MHWs, the periods with the greatest impacts of MHWs are closely related to the El Niño and La Niña periods; these impacts correspond to extreme intensities, spatial extensions that cover a large part of the ESP and durations as long as the presence of the ENSO events themselves. To quantify the drivers of MHWs, we examined the variability of the mixing layer heat balance, which largely represents the mechanisms that drive and modulate MHWs regionally in the ESP (Mechanism of air-sea heat exchange, heat advection, entrainment, and turbulent mixing in the ocean). Specifically, we studied three regions off the coast of Chile (north 18-26°S, center 26-39°S and south 39-50°S) that presented differences in the processes associated with these mechanisms. The region off northern Chile exhibited that most of its MHWs were formed primarily by a decrease in heat loss from the ocean to the atmosphere, mostly provided by a reduction in evaporation, and secondarily by an increase in thermal radiation and sensible heat flux into the ocean. Likewise, in the region off central Chile, reduced evaporation also played a dominant role in the generation of most MHWs, although here this process is combined with a considerable increase in solar radiation toward the ocean. Off southern Chile, most MHWs are generated by heat advection, dominated by anomalous southwesterly currents flowing down the mixing layer temperature gradient. In the southern region, the only atmospheric process that has a clear contribution to the MHW development is the reduction in evaporation, although it is less relevant than ocean heat advection. In addition, ocean heat advection also plays an important role in the northern and central regions, exhibiting mainly meridional and a zonal patterns, respectively. In these regions, the superposition of heat advection and air-sea heat exchange might produce MHWs of extreme characteristics. In all three regions, it appears that the entrainment process had a much lower magnitude than the other mechanisms during MHWs.
Extreme events such as Marine Heat Waves (MHWs) generate great interest both in the scientific community and in society in general. This interest arises mainly from the diverse negative impacts that MHWs have generated in all ocean basins, which produce severe socioeconomic consequences. These impacts could be even more severe and varied in future climate scenarios, with projected increases in the frequency, duration, intensity and spatial extent of MHWs due to the global warming expected by the end of the 21st century. MHWs in the Eastern South Pacific (ESP) have been less analyzed than in other regions of such ocean, so that several research initiatives in recent years (including the present work) tackle this gap. This study focuses on characterizing MHWs in the ESP and exploring the mechanisms that drive and modulate them, using the GLORYS2 and ERA-Interim global reanalysis. MHWs in the ESP are characterized by typical areas the order of 103 − 104 𝑘𝑚2 , mean area-averaged intensity anomalies of ~1.2°𝐶 and maximum anomalies reaching ~3°𝐶, and durations that exceed one month on average. Related to the driving mechanisms of MHWs, the periods with the greatest impacts of MHWs are closely related to the El Niño and La Niña periods; these impacts correspond to extreme intensities, spatial extensions that cover a large part of the ESP and durations as long as the presence of the ENSO events themselves. To quantify the drivers of MHWs, we examined the variability of the mixing layer heat balance, which largely represents the mechanisms that drive and modulate MHWs regionally in the ESP (Mechanism of air-sea heat exchange, heat advection, entrainment, and turbulent mixing in the ocean). Specifically, we studied three regions off the coast of Chile (north 18-26°S, center 26-39°S and south 39-50°S) that presented differences in the processes associated with these mechanisms. The region off northern Chile exhibited that most of its MHWs were formed primarily by a decrease in heat loss from the ocean to the atmosphere, mostly provided by a reduction in evaporation, and secondarily by an increase in thermal radiation and sensible heat flux into the ocean. Likewise, in the region off central Chile, reduced evaporation also played a dominant role in the generation of most MHWs, although here this process is combined with a considerable increase in solar radiation toward the ocean. Off southern Chile, most MHWs are generated by heat advection, dominated by anomalous southwesterly currents flowing down the mixing layer temperature gradient. In the southern region, the only atmospheric process that has a clear contribution to the MHW development is the reduction in evaporation, although it is less relevant than ocean heat advection. In addition, ocean heat advection also plays an important role in the northern and central regions, exhibiting mainly meridional and a zonal patterns, respectively. In these regions, the superposition of heat advection and air-sea heat exchange might produce MHWs of extreme characteristics. In all three regions, it appears that the entrainment process had a much lower magnitude than the other mechanisms during MHWs.
Description
Tesis para optar al grado de Magíster en Ciencias con mención en Oceanografía
Keywords
Cambios climáticos América del sur, Temperatura del océano