Posted: Dec 3, 2021 12:05 GMT
The researchers hope that understanding the phenomenon will have “a big impact” on weather forecasts for the region.
A strip of intense rain that expands each summer for more than 1,000 kilometers north from the west coast of Mexico, hits the US states of Arizona and New Mexico and sometimes reaches northern California, should not be understood “as a classic monsoon in terms of its core physics, “argue two scientists investigating the phenomenon.
According to the professors of geoscience and climatology William Boos and Salvatore Pascale, the pattern of the Asian, African and even South American monsoons is not applicable to this annual climatic event, which leaves at least half of the year’s rain in the affected territories, because It is the mountains of the Sierra Madre and a strong convection that provokes “mechanically” this intense precipitation.
A statement released on November 30 by the University of California at Berkeley explains that the scientists used a computerized model that incorporates North American weather patterns and topography, with good resolution, to test their idea of the exceptional character of this regional wet season.
The word ‘monsoon’ conjures up images of South Asian rain waves, where repeated downpours flood India and Bangladesh for several months each summer, they recall in the statement. These and other monsoons, such as those in Brazil and Africa, are generated when the intense sunlight of summer makes the atmosphere warm on the continent more than on the ocean and this imbalance draws moisture from the sea and dumps it on land in the form of intense storms.
As in the above examples, the summer rainy season in North America lasts weeks and even monthsBut detailed supercomputer simulations show that this occurs when the Sierra Madre Occidental, located near the west coast of Mexico, diverts the wet current tending to the east and redirects it upward over the mountain slopes. There the humid tropical air of the eastern Pacific cools, condenses and begins to rain.
“Big Impact” on Weather Forecasts
“The mountains on the west coast of Mexico may seem huge when you stand next to them as a human being, but they are tiny on a global scale,” Boos said. “Historically, computer simulations of Earth’s atmosphere and ocean have barely been able to take these mountains into account; it’s like trying to see the details of the teeth of an actor on television in the 1970s, “he compared.
However, the study of wind and rain patterns carried out by both authors with the application of the most modern methods available, has allowed them to obtain a higher resolution of the structure and dynamics of this monsoon and to “discover how it works”.
Behind this phenomenon, according to Boos, is “a completely different set of scientific processes to predict it, both in short-term weather forecasts and long-term climate projections “, compared to monsoon rains on other continents.
As a result of this difference, the researcher hopes that his understanding will have “a great impact” on the weather forecasts for the region and also that the forecasts of the future impact of the change in trajectory experienced in the Pacific by the mid-latitude current will be revised. because of global warming.
Boos and Pascale’s scientific article on the matter was published at the end of November.