The Azores cyclone is expanding and intensifying | Sciences

Behind the image of Mariano Medina, TVE’s first weatherman, isobars can be seen from the Azores anticyclone, especially in the north.

As crazy as it is, time has some basic factors and processes that don’t change much. One of them is Hurricane Azores. This system of high atmospheric pressure is key to the climate of the Iberian Peninsula, and it also modifies much of the climate in the rest of Western Europe and the eastern coast of the United States. Now, a study shows that in the winters of past decades, anticyclones are larger and more intense. The authors of the work even assure that such an anomaly was not seen in the last millennium, which would affect the precipitation. While acknowledging that something happened in the Azores, other climatologists don’t go that far.

To simplify this, an azure cyclone is a system of high pressures (the weight of a column of air, measured at sea level) whose epicenter is usually in the mid-Atlantic. It forms a dance partner with low-lying Iceland, the low pressure system and the source of most of the fronts that transfer ocean moisture to Europe and with it rain. These two phenomena form the opposite poles of the so-called North Atlantic Oscillation (NAO). In the summer, the couple grows up and dances north, cutting off the humidity. It is what gives the Iberian climate a dry, stable and hot environment. In winter, the Azores cyclone shrinks before Iceland declines. Its displacement to the south unleashes the storms that make Galicia a green place. But this is changing.

Recently published research in natural earth sciences It shows that the cyclone of the Azores is geographically expanding beyond its usual limits with increasing frequency. In addition, it is rising, with high pressures above averages recorded in the past. Caroline Ommenhofer is the lead author of this paper. As a scientist at Woods Hole Oceanographic Institution (USA), In their lab, they study climate variability, with a special focus on the causes of extreme events. Now they focused on the Azores anticyclone: ​​“Our study focused particularly on the winter months, as it is the main season in which the Iberian Peninsula receives the most rainfall. Changes in the magnitude and location of high pressures in the Azores during these months have had a significant impact on moisture transport from the ocean. Atlantic by guiding rain-tolerant systems,” he says in an email.

“Changes in the volume and location of the high pressures of the Azores [durante el invierno] It has a significant impact on moisture transport from the Atlantic Ocean”

Caroline Ommenhofer, Research Fellow at Woods Hole Oceanographic Institution, US

Uhmenhofer and other colleagues used different climate models to estimate winters in which high pressures exceed a threshold. They tuned it with atmospheric pressure data from weather stations scattered across the region. For example, records of Lisbon or the Azores go back to 1850. To go back further, they resorted to indirect climatic information held by stalagmites in a Portuguese cave that was forever affected by the anticyclone. They found that the number of anticyclones did not stop increasing. In the 20th century, there were 15 extreme events, in which the Azores cyclone was up to 50% larger. This phenomenon has accelerated in the winter seasons in recent decades. For comparison, in the past 1100 years, the average per century has been 9.9 high-pressure anomalies.

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“Our analyzes show that winters with a particularly massive cyclone Azores coincide with unusually dry conditions on the Iberian Peninsula during the winter,” Uhmenhofer details. By contrast, storm fronts in the North Atlantic are getting stronger further north, with Norway and the northern British Isles experiencing unusually wet conditions.

Four scientists, from paleoclimatologists to researchers from the State Meteorological Agency (AEMET) have had the opportunity to read and agree with Amnhofer’s work that something is changing in the Azores anticyclone, but they are not clear about its effect on the weather or what or who is to blame.

“The best available models for studying the climate in the last millennium show that greenhouse gases lead to the expansion and intensification of the azure anticyclone.”

Pablo Ortega, climate scientist and co-leader of the Climate Prediction Group at the Supercomputing Center in Barcelona

Climatologist and co-leader of the Climate Prediction Group at Barcelona’s Supercomputing Center, Pablo Ortega, published a paper a few years ago on how ocean circulation is impaired. About this new work he says: “The best available models for studying the climate of the last millennium [los usados en este estudio] It is observed that greenhouse gases produce expansion and intensification of the azure anticyclone, which enhances drier conditions in the Iberian Peninsula. This response to greenhouse gases could explain the changes in the azure anticyclone seen in recent decades, and the observations unambiguously explain it.”

Models are just models. It depends both on the parameters entered, on the actual feedback available to improve it, and even on computing power. This is one of the questions raised by geologist and palaeoclimatologist Armand Hernandez, who in 2020 published an investigation into the evolution of the NAO over the past 2,000 years. “They rely a lot on models and only have one observable source of information, such as speleothems. [estalactitas y estalagmitas]. They could have used other records such as lake sediments or tree rings”, believes the researcher at CICA of the University of da Coruña. For him, this weakens the conclusion that the current anomaly is the largest in the past millennium.

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Sergio M. Vicente Serrano has been studying rainfall and drought for a few years as a CSIC researcher at the Pyrenees Institute of Ecology (IPE). He acknowledges that models are necessary, but their results are not an absolute truth. In this case, he does not see a connection between the changes in the Azores and what it rains on the Iberian Peninsula. In fact, he says, “Since 1850, we’ve had wet periods alternating with other dry periods.” Another issue that is difficult to solve is guilt. For Vicente-Serrano, “there is the problem of disentangling the part that is due to climate change and which is due to the natural variability of the climate.”

AEMET’s Chief of Climate Assessment and Modeling, Esteban Rodriguez, who considers this work a solid one, agrees that something is going on with the Azores anticyclone. “There is a clear relationship between NAO status and precipitation,” he recalls. However, from existing records, dating back to the 19th century, “a rise in temperatures can be observed, but no clear trend in precipitation”.

How is it explained that the main responsible for the fact of precipitation or not is such an anomaly, however, that it is not significantly observed in the precipitation? Moreover, everything indicates that the cyclone of the Azores will continue to expand and push the bottom of Iceland further north. However, reports from the Intergovernmental Panel on Climate Change (IPCC) do not expect a decrease in precipitation.

“The NAO is responsible for 50% of the variance,” recalls Hernandez, of CICA. In other words, being the main factor, the Azores cyclone is not the only one. There are others in the jig, like melting pulling Iceland further north, and the warming Mediterranean, generating new moisture flows…For Rodríguez, of AEMET, climate change is “creating a new scenario.”

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Aileen Morales

"Beer nerd. Food fanatic. Alcohol scholar. Tv practitioner. Writer. Troublemaker. Falls down a lot."

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