In 1995 during the WOCE Indian Ocean Expedition, wind speeds in the southern half of the Arabian Sea in June were about 2 m s−1 below normal and in September the southern one-third of the Arabian Sea was 1 m s−1 above normal (Fig. Subsequent analyses use SSMI/AM data which, when compared with SSMI/PM, had greater agreement with 2-day, 1° × 1° NSCAT data. 1999). 4) and India west coast rainfall (Fig. Not very helpful in learning about jet streams.

Polar-Night Jet Stream Mon. Monsoon wind onset time is not the same throughout the Arabian Sea (Halpern and Woiceshyn 1999). Average onset times for the Somali Jet during five El Niño and four La Niña episodes were 1 June and 29 May, respectively.

Oceanogr., 29, 1619–1623, Hastenrath, S., 1991: Climate Dynamics of the Tropics. Please go to Your Account page and enter a Username in the "Create a Username" text field. The SSM/I 10-m height wind speed data product is continuous, except for December 1987–January 1988, which has no influence on the analysis. Nature, 401, 356–360, Wentz, F. J., 1992: Measurement of oceanic wind vector using satellite microwave radiometers. We are indebted to the tremendous accomplishment by Frank Wentz and his colleagues at Remote Sensing Systems for reprocessing and timely updating of the entire SSM/I wind speed data record. The Somali Jet monthly mean wind speed anomaly is equal to the mean wind speed anomaly associated with the geographical region where monthly mean wind speeds were greater than 10 m s−1. The Somali Ocean Current • Atmospheric changes over the southern Pacific Ocean led to warmer than usual waters flowing into the Indian Ocean. We described the intraseasonal oscillation occurrence as “serendipitous” because interannual variations of the strength and phase of intraseasonal oscillations are unpredictable (Slingo et al. We Genuinely APPRECIATE your PATIENCE. The minimum low atmospheric pressure would, as compared with La Niña, be greater in El Niño and would reach its minimum at a later date. Phys., 70, 201–213, Saji, N. H., B. N. Goswami, P. N. Vinayachandran, and T. Yamagata, 1999: A dipole mode in the tropical Indian Ocean.

In addition, precipitation often increases in Europe because the jet stream is stronger in the Northern Atlantic and is capable of pushing them farther east. What is a Jet Stream? Found this particularly challenging. • It was observed to flow from Mauritius and the northern part of the island of Madagascar before reaching the coast of Kenya at about 3º S. Subsequently it ran over the plains of Kenya, Ethiopia and Somalia before reaching the coast again around 9º N. Over Asia in summer, the subtropical jet is replaced by the tropical easterly jet stream. The questions on the test, a few that were asked weren't mentioned in the text it felt like. 1999). Added notions for aviation clear air turbulence and tropical cyclone formation. Halpern, D., and P. M. Woiceshyn, 2001: Somali Jet in the Arabian Sea, El Niño, and India Rainfall. Months used to determine El Niño or La Niña conditions associated with the onset of the Somali Jet were 2 months prior to the month in which onset occurred plus the onset month.

The onset time of the Somali Jet was 2 days later during El Niño as compared with La Niña (Fig. Sub-tropical Westerly and Tropical Jet Streams • The end of the monsoon season is brought about when the atmosphere over the Tibetan Plateau begins to cool; this enables the STJ to transition back across the Himalayas. J. Climate, 14, 434–441, https://doi.org/10.1175/1520-0442(2001)014<0434:SJITAS>2.0.CO;2. The Somali Jet is the narrow southwesterly surface wind with a 2-day average speed greater than 12 m s −1 (Halpern and Woiceshyn 1999); the cross-stream 1/e dimension of the Somali Jet is about 200 km. The level of physical oceanographic significance between monthly mean wind speeds is 1 m s−1 (Halpern et al. • The difference in heating and cooling and the ensuing pressure gradient is what drives this jet stream. However, June 1997 was also coincident with an extensive warming of the Indian Ocean that Webster et al. • Further to the north the polar jet stream stalled due to being countered by Rossby Waves, there was a large kink in the stream and this was centred over Russia. Halpern and Woiceshyn (1999) suggested that the Somali Jet in the Arabian Sea and India west coast rainfall accumulation may have a causal relationship because of simultaneous increases in surface wind convergence and integrated cloud liquid water in the eastern Arabian Sea.

1994). Part I: Surface Climate and Atmospheric Circulation.

1. For 1988–97, we obtained India Meteorological Department (IMD) daily rainfall at Vengurla and Panjim, two coastal sites separated by 50 km near 15°N. The strength of the Somali Jet was about 0.4 m s−1 lower during El Niño than in La Niña (Fig. 1999) for June, July, August, and September during 1988–98. In July the Somali Jet covered 55% of the Arabian Sea. In July and September, the India west coast received 745 and 1160 mm, respectively, more rain during La Niña as compared with El Niño. We are thankful to Michael Halpert and to the IMD-Pune Additional Director General for Meteorology (Research) for making available monthly mean 2° × 2° rainfall data and daily rainfall data at Panjim and Vengurla, respectively.

Monthly Niño-3 sea surface temperature anomalies were electronically retrieved from ftp://nic.fb4.noaa.gov/pub/cac/cddb/indices/sstoi.indices.

Climatol., 18, 775–791, Krishnamurti, T. N., P. Ardanuy, Y. Ramanathan, and R. Pasch, 1981: On the onset vortex of the summer monsoon. The mean 1988–97 India west coast rainfall accumulations in June (4297 mm), July (5476 mm), August (3165 mm), and September (1501 mm) were used to compute monthly mean rainfall accumulation anomalies. For the same surface wind speed and direction, the SSM/I on a descending orbit would retrieve a slightly different pattern of radiation than that recorded on an ascending orbit because the apparent surface wind directions associated with descending and ascending orbits differ by 180°. • During summer, in the Northern Hemisphere, the subtropical jet weakens considerably, and it is only identifiable in sporadic velocity streaks around the globe. In July and August, a stronger Somali Jet was accompanied with an excess of India west coast rainfall of 605 and 815 mm, respectively, in comparison with the rainfall when the Somali Jet intensity was below normal. With the jet stream stalled the STJ was unable to transit across the Himalayas as it would do ordinarily, the monsoon cell to the south, fed by warmer waters in the Indian Ocean, had nowhere to go and as a consequence it deposited vast amounts of rain over Pakistan, Himachal Pradesh and Jammu and Kashmir and this led to extensive flooding.

Please wait... Aviation They all share the notion that the northward advection of planetary vorticity across the equator, coupled with the presence of a north-south mountain barrier, leads to the formation of a low-level western boundary current (akin to the Gulf-Stream) along the equatorial east coast of Africa.

How do the Jet Streams affect the Monsoons and the Indian Sub Continent? Lack of clear explanation.

Corresponding author address: Dr. David Halpern, Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109-8099. Kluwer, 488 pp, ——, and P. J. Lamb, 1979: Climatic Atlas of the Indian Ocean.

This leads to the formation of a cyclonic winter monsoon cell typified by sinking air masses over India and relatively moisture free winds that blow seaward. 1999), which illustrates the complexity of the monsoon and the difficulty to predict its interannual variability. • With respect to the monsoons of India it is the Subtropical Jet Stream (STJ)and the countering Easterly Jet that are most important. Wind speed anomaly differences between month-to-month distributions within a specific year (Fig.

Therefore, the surface temperatures determine where the jet stream will form.

For more information about sharing your work with Kudos, please visit our Kudos information page. Included are discussions of their formation, maintenance, influence on synoptic weather, and role in the general circulation. • Conversely, during La Nina events, California dries out and precipitation moves into the Pacific Northwest because the polar jet stream moves more north. El Niño or La Niña is not defined when the 3-month average Niño-3 sea surface temperature anomaly was less than |0.2|°C.

1). The zonal component of wind direction must be eastward. For a 2-day SSMI/AM wind speed of 12 m s−1, the SSMI/PM speed predicted with a least square linear orthogonal regression analysis was 13.7 m s−1. J. Climate, 7, 81–105, Ju, J., and J. Slingo, 1995: The Asian summer monsoon and ENSO. The June 1994 Niño-3 sea surface temperature anomaly was too small for classification as El Niño or La Niña. • This ocean current named the Somali Current, flows northward from the equator to 9º N, where it separates from the coast. Wea. Monsoon onset has a duration of 6 days for wind in the Arabian Sea (Halpern and Woiceshyn 1999) and 3 days for rainfall in India (Das 1987).

1), we found another source of onset times.

Over the Indian subcontinent, there are a number of separate jet streams whose speed varies from 110 km/h in summer to about 184 km/h in winter. Also, Annamalai and Slingo (1998) reported the June–September 1997 Somali Jet at 850 hPa was weaker than normal. Meteor. At 60°–90°E, Slingo (1998), using an NWP data product, reported an intense westerly wind burst at 850 hPa during the first two weeks of May 1997 and easterly winds in early June 1997, which would reduce southwest monsoon wind speeds in the southern Arabian Sea to delay the onset of the 12 m s−1 isotach.

The very late arrival of the Somali Jet in 1997 produced the two largest year-to-year fluctuations of onset time. Fan, 1999: Choice of South Asian summer monsoon indices. Very insightful lesson.

Fieux and Stommel (1977) reported that 25 May, with a ±5-day uncertainty, is the average date of onset of monsoon winds in the Arabian Sea about 500 km northeast of Somalia. The position and strength of the jet stream then helps meteorologists forecast future weather events. Bull.

SIGNIFICANCE OF THE JET STREAM 4, the 1988–97 average value of the Somali Jet wind speed anomalies for a specific month was not zero because the monthly mean areal extent and geographical domain of the Somali Jet were not constant.

University of Wisconsin Press, 116 pp, Joseph, P. V., J. K. Eischeid, and R. J. Pyle, 1994: Interannual variability of the onset of the Indian summer monsoon and its association with atmospheric features, El Niño, and sea surface temperature anomalies. The June, July, August, and September Somali Jet monthly mean wind speed anomalies during El Niño were 0.2, 0.0, −0.2, and 0.5 m s−1 smaller than that during La Niña (Fig. An adaptation of the Arpe et al. (1997), who measured upper-ocean currents along 8°30′N to estimate the wind-driven component of the circulation, were not normal.

The average date of onset during 1988–97 was 30 May.

Res.

Tropical Easterly Jet Stream

The 1988–99 period includes episodes of El Niño and La Niña, but not a sufficient number of events occurred for results to have reliable statistics. This adds moisture bearing winds to the southwest monsoon. The altitude of the mountains initially disrupts the jet but once it has cleared the summits it is able to reform over central Asia.