Агаар мандлын таагүй нөхцөл байдал болон Номхон далайн температурын өөрчлөлт нь энэ жилийн хар салхины улирлыг сүүлийн жилүүдийн хамгийн нам гүм үе болгож байна.
Атлантын далайн бүс нутагт зургаадугаар сараас хойш ердөө гурван нэр бүхий шуурга бүртгэгдсэн нь олон жилийн дунджаас эрс бага үзүүлэлт юм. Ажиглалтын мэдээллээр, энэ улирлын хуримтлагдсан циклоны эрчим (ACE) ердөө 3.1 нэгж байгаа нь наймдугаар сарын дунд үеийн дунджаас 23 хувиар бага байна. Цаг уурчид энэ жил 10-аас цөөн нэр бүхий шуурга үүсэх төлөвтэй байгааг таамаглаж байна.
Энэхүү нам гүм байдалд Номхон далайн экваторын бүс дэх усны хэм дунджаас 1.5-4 хэмээр дулаарсан “Эль-Ниньо” үзэгдэл гол нөлөө үзүүлж байна. Энэхүү дулаарал нь агаарын дээд давхаргын салхины урсгалыг өөрчилж, Атлантын далай дээгүүр хүчтэй салхи (wind shear) үүсгэдэг. Ийм хүчтэй салхи нь үүсэж буй аянга цахилгаантай шуурганы бүтцийг эвдэн, хар салхи болж өргөжих боломжийг нь хаадаг ажээ.
Үүнээс гадна Африкийн эргээс салхилах хуурай, тоостой агаарын урсгал болон Баруун Африкийн муссоны сулрал нь хар салхи үүсэх нөхцөлийг улам бүр хязгаарлаж байна. Сахарын цөлийн хуурай агаар нь агаар мандалд “бүрхүүл” үүсгэж, шуурганы хөгжлийг дарангуйлдаг. Эдгээр хүчин зүйлсийн нөлөөгөөр Атлантын далайд 2013 оноос хойших хамгийн идэвхгүй улирал ажиглагдаж байна.
Гэсэн хэдий ч мэргэжилтнүүд Эль-Ниньотой жилүүдэд хүчтэй хар салхи үүсэх эрсдэл бүрэн арилаагүй гэдгийг анхааруулж байна. Өнгөрсөн хугацаанд ийм нөхцөлд ч аюултай шуурганууд бүртгэгдэж байсан тул эргийн бүс нутгийн оршин суугчид цаг агаарын урьдчилсан мэдээг тогтмол хянаж, болзошгүй аюулд бэлэн байх шаардлагатайг зөвлөж байна.
Дэлгэрэнгүйг эх сурвалжаас харах
↓Эх сурвалжийг нээх ↓
It’s the middle of Atlantic hurricane season, but you’d be forgiven for forgetting that it’s even happening.
The basin has only seen three named storms since the start of hurricane season in June, a trio of weak and largely disheveled tropical storms. One or two additional tropical storms are possible through the middle of August as the season struggles against a bevy of unfavorable conditions.
They include this year’s El Niño, which is on its way to making history as sea surface temperatures soar to unprecedented heights across a critical swath of the Pacific Ocean, as well as persistent puffs of dry, dusty air that are blowing off the coast of Africa.
Together, these distant forces are working to stifle any opportunity for tropical storms to develop across the Atlantic basin. Forecasters now expect one of the quietest hurricane seasons in years, with fewer than 10 named storms likely to sneak through the unfavorable conditions.
Experts have been stunned by how fast El Niño has intensified this summer. This pattern of warmer-than-normal waters around the equator in the eastern and central Pacific significantly alters global weather patterns.
El Niño requires water temperatures in a key region around the equator to run at least 0.5 degrees Celsius (0.9 degrees Fahrenheit) above normal for several consecutive months. Measurements show that this swath of the Pacific is at least 1.5 degrees Celsius above average for this time of year, with portions of the region seeing astonishing anomalies of as much as 4 degrees Celsius above normal.
Abnormally warm waters in the Pacific Ocean lead to widespread pockets of rising air in the region, which alter the upper-level wind patterns. Increased convection over the Pacific, combined with the readjusted upper-level wind patterns, work together to send stronger-than-usual winds blowing east over the Atlantic basin—a phenomenon known as wind shear.
Thunderstorms are the seeds from which a tropical system grows. Strong winds aloft disrupt the structure of a budding thunderstorm, which ultimately prevents individual storms from organizing into a tropical system.
These same conditions are having the opposite impact on tropical cyclone activity across the steamy Pacific Ocean. The western Pacific typhoon season was busier by the beginning of August than any season in almost 50 years. Four storms across the region reached the equivalent strength of a Category 5 storm, including Sinlaku in April and Bavi, Dolphin, and Genevieve in July. The central and eastern Pacific are also hopping, with the US National Hurricane Center expecting above-average activity in this region through autumn.
But El Niño isn’t the only factor putting a crimp in this year’s Atlantic hurricane season this year. The West African monsoon is usually a key player in sending thunderstorms streaming over the Atlantic that can later turn into tropical systems. But this year’s monsoon has been a bit lackluster this year, with below-average rainfall in places like Sierra Leone and Guinea signaling that we’re seeing weaker disturbances than usual.
The Sahara Desert is also limiting this hurricane season’s already meager potential. Intrusions of dry, dusty air keep blowing east to west across the Atlantic, acting like a lid on the atmosphere that’s suppressing most opportunities for thunderstorm development.
Together, these factors are working together to produce the least active Atlantic hurricane season since at least 2013. Forecasters use a metric known as Accumulated Cyclone Energy (ACE) to quantify a season based on the intensity and longevity of its storms. An average Atlantic hurricane season produces an overall ACE of 122.5. This season has so far produced an ACE of 3.1, which is just 23 percent of average for the middle of August.
Fewer storms doesn’t mean zero storms, though, and El Niño years have a history of producing intense and devastating hurricanes despite unfavorable conditions overall. Despite its struggle, this year’s Tropical Storm Arthur still may have broken Louisiana’s 24-hour rainfall record with more than 29 inches of rain reported near the community of Cottonport. And in the past, Hurricanes Camille, Ivan, Charley, Michael, Idalia, and Lee all occurred with El Niño conditions present. That means coastal residents should continue monitoring forecasts and have plans in place in case a storm does threaten land.
