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Abstract The relationship of upper tropospheric jet variability to El Niño / Southern Oscillation (ENSO) in reanalysis datasets is analyzed for 1979–2018, revealing robust regional and seasonal variability. Tropical jets associated with monsoons and the Walker circulation are weaker and the zonal mean subtropical jet shifts equatorward in both hemispheres during El Niño, consistent with previous findings. Regional and seasonal variations are analyzed separately for subtropical and polar jets. The subtropical jet shifts poleward during El Niño over the NH eastern Pacific in DJF, and in some SH regions in MAMand SON. Subtropical jet altitudes increase during El Niño, with significant changes in the zonal mean in the NH and during summer/fall in the SH. Though zonal mean polar jet correlations with ENSO are rarely significant, robust regional/seasonal changes occur: The SH polar jet shifts equatorward during El Niño over Asia and the western Pacific in DJF, and poleward over the eastern Pacific in JJA and SON. Polar jets are weaker (stronger) during El Niño in the western (eastern) hemisphere, especially in the SH; conversely, subtropical jets are stronger (weaker) in the western (eastern) hemisphere during El Niño in winter and spring; these opposing changes, along with an anticorrelation between subtropical and polar jet windspeed, reinforce subtropical/polar jet strength differences during El Niño, and suggest ENSO-related covariability of the jets. ENSO-related jet latitude, altitude, and windspeed changes can reach 4(3)°, 0.6(0.3) km, and 6(3) ms −1 , respectively, for the subtropical (polar) jets.
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Orbital Forcing Strongly Influences the Poleward Shift of the Spring Himalayan Jet During the Past Millennium
Abstract The latitudinal position of the subtropical jet over the Himalayas (Himalayan jet latitude or HJL) controls the region's climate during winter and spring by guiding moisture‐delivering storms. Here we use the Community Earth System Model‐Last Millennium Ensemble to diagnose forced trends in HJL during the past millennium. During 850–1849, there is a weak equatorward trend in winter HJL. In contrast, the spring HJL has a relatively larger poleward trend, and increases in both variance and frequency of poleward/equatorward excursions. We demonstrate changes in orbital precession reduced the thermal gradient between tropical and subtropical Asia, shifting the spring HJL poleward. During 1850–2005, the spring HJL exhibits no trend due to compensating influences from orbital and anthropogenic greenhouse gas forcings. These findings suggest it is essential climate models properly simulate the effects of and potential interactions between orbital forcing and anthropogenic factors to accurately project Himalayan jet variability and associated storm tracks.
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- Award ID(s):
- 1805143
- PAR ID:
- 10367496
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 49
- Issue:
- 3
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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