Cool-season occurrences of blocks, extratropical cyclones that undergo explosive cyclogenesis, and tropical cyclones (TCs) that undergo extratropical transition (ET) from 1980 to 2015 are analyzed using the National Aeronautics and Space Administration’s Modern-Era Retrospective Analysis for Research and Applications, version 2, dataset. These synoptic events are first examined in a climatological analysis that includes identifying consecutive synoptic events, namely, blocks that follow bombs or ET events as well as extratropical cyclones that follow ET events. These synoptic events are then analyzed with respect to three tropical modes of variability: the Madden–Julian oscillation (MJO), El Niño–Southern Oscillation, and the stratospheric quasi-biennial oscillation (QBO). The QBO was considered from both a momentum and thermal point of view, using the equatorial 30-hPa zonal-mean wind and the equatorial zonal wind shear between 30 and 50 hPa, respectively. The results show that in the seven days prior to cool-season blocks and ET events, there is a statistically significant frequency minimum in MJO phases 7 and 3, respectively. With respect to the QBO, there is a statistically significant frequency maximum in neutral QBO conditions during bomb onset and a frequency minimum during ET onset. When stratifying bombs by latitude, there is a significant reduction in Arctic (i.e., poleward of 55°N) bomb onset during easterly QBO conditions. The results show that both tropospheric and stratospheric tropical modes of variability can modulate the frequency of extratropical synoptic events to a similar degree.
Relative contributions to the zonal mean meridional heat transport by the climatological annual mean, climatological annual variation, synoptic, intra‐seasonal and lower‐frequency motions were examined based on the ERA‐Interim reanalysis data for the period of 1981–2015. The meridional heat transport analysed in this study only includes the component related to meridional wind and temperature. In the tropics, the climatological annual mean circulations dominate the long‐term mean meridional heat transport, while the interaction between the climatological annual mean temperature and the seasonal anomalous flow largely contributes to the seasonal variation of the meridional heat transport. In the middle latitudes, the climatological annual mean circulations and transient eddies (mostly synoptic and intra‐seasonal eddies) are of roughly equal importance in the poleward heat transport, leading to the maximum poleward heat transport around 50°N/S. The upper‐ and lower‐tropospheric heat transports by the climatological annual mean circulations appear opposite, with the magnitude of the lower‐tropospheric transport being greater. The preferred maximum zonal mean heat transport at 50°N by the climatological mean flow is attributed to the maximum zonal mean low‐level southerly in situ. The preferred peak latitude of the mid‐latitude poleward heat transport by synoptic eddies near 50°N arises from the combined effect of the strong synoptic‐scale meridional wind and temperature variabilities in situ and their in‐phase relationship. The heat transport by tropical cyclones (TCs) was estimated by applying a statistical relationship between TC intensity and the vertically integrated temperature averaged over the TC core region derived from high‐resolution Weather Research and Forecasting (WRF) model simulations. For northern hemisphere summer, TCs contribute about 35% of the total heat transport in the active TC regions, suggesting that TCs play a critical role in the regional meridional heat transport.
more » « less- NSF-PAR ID:
- 10364368
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- International Journal of Climatology
- Volume:
- 42
- Issue:
- 4
- ISSN:
- 0899-8418
- Page Range / eLocation ID:
- p. 2153-2168
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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