Easterly jet stream

June is typically a quiet month for tropical development across the Atlantic. Historically, only about 6% of all named storms form in June, compared to August, September, and October, which each see about 25%, 35%, and 20% of all named storm formations respectively (80% of named storms and 94% of Category 3, 4, and 5 hurricanes form from August through October). That means we’d expect a named storm about every one to two years in June – on par with November, the other bookend of the hurricane season. We know a few things about tropical climatology to help us narrow our focus in June. In general, wind shear is the biggest prohibitive factor to tropical formation this time of year. The subtropical jet stream is usually still too powerful for storm formation over the warmer tropical waters. Average wind shear for June 15th to June 30th (1991-2020 averages). So while the deep tropical Atlantic systems (primarily spawned from African Easterly Waves or AEWs) comprise 50% to 60% of Atlantic named storms and some 85% of our strongest (Category 3 or stronger) hurricanes, they’re usually not a major player until late July and August. It explains why you see only a smattering of formation points east of the Caribbean islands in the map at the top of this article. Average number of tropical systems that form from deep tropical African Easterly Waves (AEW) by month. June and November typically see the fewest storms arising from tropical waves. Credit: Erica Staehling/Princeton Universi...

PRINTED FROM OXFORD REFERENCE (www.oxfordreference.com). (c) Copyright Oxford University Press, 2023. All Rights Reserved. Under the terms of the licence agreement, an individual user may print out a PDF of a single entry from a reference work in OR for personal use (for details see date: 15 June 2023 Equatorial Jet Stream Source: A Dictionary of Weather Author(s): Storm Dunlop An easterly jet stream that develops in the eastern hemisphere, at approximately 10° N, during the northern summer (particularly in the months of July and August). It lies at altitudes of 15–20 km, and extends from Asia to Africa, but is not observed over the western hemisphere. It arises because of the steep temperature gradient from north to south in the upper troposphere—the coldest air lying over the Equator. A weaker, broad, low-level easterly jet, at 4–5 km altitude, may form over Africa during the same period and at approximately the same latitude. Oscillations beneath this jet create westward-moving ... ... Access to the complete content on Oxford Reference requires a subscription or purchase. Public users are able to search the site and view the abstracts and keywords for each book and chapter without a subscription. Please If you have purchased a print title that contains an access token, please see the token for information about how to register your code. For questions on access or troubleshooting, please check our PRINTED FROM OXFORD REFERENCE (www.oxfordreference.com). (c) Copyright Ox...

Rao , B. R. S. , D. V. B. Rao , and V. B. Rao , 2004 : Decreasing trend in the strength of tropical easterly jet during the Asian summer monsoon season and the number of tropical cyclonic systems over Bay of Bengal . Geophys. Res. Lett. , 31 , L14103 , doi:10.1029/2004GL019817 .)| false• Search Google Scholar • Export Citation • Rao , V. B. , C. C. Ferreira , S. H. Franchito , and S. S. V. S. Ramakrishna , 2008 : In a changing climate weakening tropical easterly jet induces more violent tropical storms over the north Indian Ocean . Geophys. Res. Lett. , 35 , L15710 , doi:10.1029/2008GL034729 .)| false• Search Google Scholar • Export Citation • Fig. 1. Climatological mean of June–September (JJAS) for the period 1950–2009. (a) Wind at 150 hPa (m s −1) is shown by the vectors and magnitudes shown in color. The dashed line box marked A denotes the area covered by the TEJ. To its north are the Tibetan anticyclone (B) and the Asian subtropical jet stream (C). (b) Mean temperature at 200 hPa for the subtropical region (D) and for the equatorial area (E). (c) Temperature change at 200 hPa (2000–09 minus 1950–59). Here G and H represent the subtropical cooling and F denotes equatorial warming. (d) The shaded grid cells denote the regions of statistical significance at 95% level. • Fig. 3. Annual variation of the 200-hPa temperature of the (a) equatorial and (b) subtropical boxes. (c) Strength of the Hadley circulation as the difference of the meridional winds of JJAS aver...

In this study, we demonstrate a new mechanism, on how the warm phase of El Niño and Southern Oscillation (ENSO) delays the Indian Summer Monsoon onset through coupled ocean-atmospheric processes. Strong basin-wide warming is prominent over North Indian Ocean (NIO) during the El Niño years. The warming is intense over the South West Indian Ocean (SWIO) due to the westward propagation of the equatorial Rossby waves from the Pacific Ocean. It increases the convective activities over the southern tropical Indian Ocean (0–10° S), adjacent to the SWIO region. The warming over the SWIO and the NIO strengthens the divergent wind from the Indian Ocean to the sub-tropics via a wind-evaporation-SST feedback mechanism, which causes more upper-level convergence within 30° N latitudes. Besides, a warmer Indian Ocean enhances the upper-level diabatic heating over the southern Arabian Peninsula and Eastern Indian landmass. These factors strengthen but shift the local Hadley circulation over the Indian Ocean more southward, with an ascending branch centered over the SWIO region. The shifting of the local Hadley circulation during the El Niño years causes the Sub Tropical Jet (STJ) to migrate more southward and centered more over the Indian subcontinent. This southward movement of the STJ over the Indian subcontinent in response to the El Niño condition inhibits the establishment and propagation of the tropical easterly jet during the monsoon season, which subsequently hinders the monsoon c...

The West African monsoon is the alternation of the southwesterly wind and the harmattan at the surface. Such alternation is normally found between latitudes 9° and 20° N. Northeasterlies occur constantly farther north, but only southwesterlies occur farther south. Except for Differences from other monsoon systems The moist southwesterly stream, particularly frequent between 5° and 10° N, can reach much farther north, bringing warm humid nights and moderately hot but still humid days. The harmattan brings cooler nights, but the extreme daily heating causes a thermal range of 10–12 °C (18–22 °F). Even in the daytime, the harmattan may give a sensation of coolness to the The advancing If it were not for the change in wind direction when the southeast trades have crossed the Equator, the monsoon system of West Africa could not be distinguished from the weather system, caused by the seasonal shift in the latitude of the Toward the north, conditions are more distinctly monsoonal: by latitude 8° N the two wet seasons have merged into one long “wet” with two subdued peaks, which last approximately seven to eight months (March–October). The “dry,” which is controlled by northeast winds, lasts from November to early March. There is one rainfall maximum (in August or September) only a short distance farther north, although the wet season is only a few weeks shorter.

As the high-sun season (that is, the Northern Hemisphere summer) moves northward during April, India becomes particularly Also in May, the dry surface of Peak period During June the easterly jet becomes firmly established at 150 to 100 millibars, an atmospheric pressure region typically occurring at elevations between 13,700 and 16,100 metres (45,000 and 53,000 feet). It reaches its greatest speed at its normal position to the south of the anticyclonic ridge, at about 15° N from Most spectacular clouds and rain occur against the Get a Britannica Premium subscription and gain access to exclusive content. Various factors, especially Later, in June and July, the monsoon is strong and well-established to a height of 6,000 metres (less in the far north), with occasional thickening to 9,000 metres. It is mainly in July and August that waves of A totally different development arises when the easterly jet moves farther north than usual. The monsoonal wind rising over the southern slopes of the Himalayas brings heavy rains and local floods. The weather over the central and southern districts, however, becomes suddenly drier and remains so for as long as the abnormal shift lasts. The opposite shift is also possible, with midlatitude upper air flowing along the south face of the Himalayas and bringing drought to the northern districts. Such dry spells are known as “breaks” of the monsoon. Those affecting the south of India are similar to those experienced on the see Monsoon withdrawal