This case study aims at examining the waveguide formation by the subtropical jet (STJ) of the Northern Hemisphere and the way it may be influenced by the large-scale oscillations associated with ENSO, IOD, and QBO in the two selected months of February and November for the period 1940 to 2024. To this end, the refractive index diagnostic is employed to determine Rossby waveguides. Further, the formation of circumglobal Rossby wave trains is assessed using the variances of the bandpass filtered (2-6 days) meridional wind at 850 hPa pressure level. The analysis is guided by the principle that a strong, zonally oriented STJ can act as a waveguide. For both the formation of sufficiently strong STJ over the North Atlantic and the circumglobal wave trains, the establishment of the negative phase of the North Atlantic Oscillation (NAO) is shown to be essential. In this connection, a negative NAO helps to direct the transients in a zonal track across the southern part of North Atlantic. Results show that while moderate to strong El Niño events tend to provide the required negative NAO, in super El Niño events like those of 1982, 1998, and 2015, the positive NAO is developed and the circumglobal wave pattern is disrupted across the Atlantic sector. Also, when moderate to strong El Niño, the negative IOD and westerly shear of QBO all happen in the same month, especially in February, STJ is more likely to act as a zonal waveguide for Rossby waves. The formation of the circumglobal wave train could happen when only one of the three teleconnections was in favorable phase, as results for November 1995 suggest. In comparison between the two months, a stronger connection was found in February between the upper-tropospheric waveguide and the circumglobal wave train.

This case study aims at examining the waveguide formation by the subtropical jet (STJ) of the Northern Hemisphere and the way it may be influenced by the large-scale oscillations associated with ENSO, IOD, and QBO in the two selected months of February and November for the period 1940 to 2024. To this end, the refractive index diagnostic is employed to determine Rossby waveguides. Further, the formation of circumglobal Rossby wave trains is assessed using the variances of the bandpass filtered (2-6 days) meridional wind at 850 hPa pressure level. The analysis is guided by the principle that a strong, zonally oriented STJ can act as a waveguide. For both the formation of sufficiently strong STJ over the North Atlantic and the circumglobal wave trains, the establishment of the negative phase of the North Atlantic Oscillation (NAO) is shown to be essential. In this connection, a negative NAO helps to direct the transients in a zonal track across the southern part of North Atlantic.