The present study investigates how changes in the Hadley Cell (HC) intensity impact the stationary Rossby waves energy propagation in the Southern Hemisphere (SH) extratropics. Composites for weak and strong HC Intensity Index (HCI) were used in this analysis. The results for weak HC cases showed a wave train emanating from the subtropical central-west Indian Ocean in an arc-like route, with zonal wavenumber three in the polar jet waveguide, and reaching the north of South America. For strong HC cases, the wave train is also trapped inside the polar jet waveguide with zonal wavenumber four, emanating from subtropical central-east Indian Ocean and reaching the subtropical west coast of Africa. A weaker zonally oriented wave train with zonal wavenumber five has been found in the subtropical region with opposite polarity for weak and strong HC cases. Over the South America, the results show that an HC weakening can lead to a very cold and rainy winter in the southwest of the continent and a mild warm and dry winter on Brazilian states of Minas Gerais and Bahia. A pattern almost opposite was observed when the CH strengthens. 1. Introduction The Hadley Cell (HC) plays a key role in the climate system. Generally defined as the zonal mean meridional mass circulation in the atmosphere bounded roughly by 30°S and 30°N, with warmer air rising in the tropics and colder air sinking in the subtropics, this circulation transports momentum flux to the subtropics and heat from the tropics to the subtropics and to high latitudes through extratropical eddies. Both heat and momentum transports have important influences on subtropical jet streams, which consequently impact on waves and atmospheric circulations at middle and high latitudes [1]. In particular, upper level jet streams play an important role acting as waveguides for the Rossby waves [2]. Moreover, the deep convection in the rising branch of the HC and the associated divergence at high levels results in a meridional displacement of the air parcels, which causes a disturbance in the vorticity field and then, by absolute vorticity conservation a Rossby wave is generated. Thus, tropical variability affects the extratropical atmospheric circulation due to the generation of Rossby waves that propagate from the tropics into the extratropics in a westerly background flow [2–4]. Marengo et al. [5] found that stationary Rossby waves emanating from the western tropical Pacific during wintertime can lead to cooling and occurrence of freezes in south-eastern South America. Müller and Ambrizzi [6] found, in the austral
References
[1]
Y. Hu and C. Zhou, “Decadal changes in the Hadley circulation,” Advances in Geosciences, vol. 16, pp. 61–71, 2008.
[2]
B. J. Hoskins and T. Ambrizzi, “Rossby wave propagation on a realistic longitudinally varying flow,” Journal of the Atmospheric Sciences, vol. 50, no. 12, pp. 1661–1671, 1993.
[3]
R. J. Haarsma and F. Selten, “Anthropogenic changes in the Walker Circulation and their impact on the extra-tropical planetary wave structure,” Climate Dynamics, vol. 39, no. 7-8, pp. 1781–1799, 2012.
[4]
B. J. Hoskins and D. J. Karoly, “The steady linear response of a spherical atmosphere to thermal and orographic forcing,” Journal of the Atmospheric Sciences, vol. 38, no. 6, pp. 1179–1196, 1981.
[5]
J. A. Marengo, T. Ambrizzi, G. Kiladis, and B. Liebmann, “Upper-air wave trains over the Pacific Ocean and wintertime cold surges in tropical-subtropical South America leading to Freezes in Southern and Southeastern Brazil,” Theoretical and Applied Climatology, vol. 73, no. 3-4, pp. 223–242, 2002.
[6]
G. V. Müller and T. Ambrizzi, “Teleconnection patterns and Rossby wave propagation associated to generalized frosts over southern South America,” Climate Dynamics, vol. 29, no. 6, pp. 633–645, 2007.
[7]
J. Lu, C. Deser, and T. Reichler, “Cause of the widening of the tropical belt since 1958,” Geophysical Research Letters, vol. 36, no. 3, Article ID L03803, 2009.
[8]
J. Lu, G. A. Vecchi, and T. Reichler, “Expansion of the Hadley cell under global warming,” Geophysical Research Letters, vol. 34, no. 14, Article ID L14808, 2007.
[9]
Y. Hu and Q. Fu, “Observed poleward expansion of the Hadley circulation since 1979,” Atmospheric Chemistry and Physics, vol. 7, no. 19, pp. 5229–5236, 2007.
[10]
T. J. Reichler and I. M. Held, “Evidence for a widening of the Hadley cell,” in Proceedings of the 17th AMS Conference on Climate. Variability and Change, American Meteorological Society, Cambridge, Mass, USA, 2005.
[11]
D. J. Seidel, Q. Fu, W. J. Randel, and T. J. Reichler, “Widening of the tropical belt in a changing climate,” Nature Geoscience, vol. 1, no. 1, pp. 21–24, 2008.
[12]
T. Reichler, “Changes in the atmospheric circulation as indicator of climate change,” in Climate Change: Observed Impacts on Planet Earth, T. M. Letcher, Ed., pp. 145–164, Amsterdam, The Netherlands, 2009.
[13]
G. A. Vecchi and B. J. Soden, “Global warming and the weakening of the tropical circulation,” Journal of Climate, vol. 20, no. 17, pp. 4316–4340, 2007.
[14]
T. Ambrizzi, B. J. Hoskins, and H.-H. Hsu, “Rossby wave propagation and teleconnection patterns in the austral winter,” Journal of the Atmospheric Sciences, vol. 52, no. 21, pp. 3661–3672, 1995.
[15]
M. Kanamitsu, W. Ebisuzaki, J. Woollen et al., “NCEP-DOE AMIP-II reanalysis (R-2),” Bulletin of the American Meteorological Society, vol. 83, no. 11, pp. 1631–1643, 2002.
[16]
H. L. Tanaka, N. Ishizaki, and A. Kitoh, “Trend and interannual variability of Walker, monsoon and Hadley circulations defined by velocity potential in the upper troposphere,” Tellus A, vol. 56, no. 3, pp. 250–269, 2004.
[17]
A. H. Oort and J. J. Yienger, “Observed interannual variability in the Hadley circulation and its connection to ENSO,” Journal of Climate, vol. 9, no. 11, pp. 2751–2767, 1996.
[18]
D. E. Waliser, Z. Shi, J. R. Lanzante, and A. H. Oort, “The Hadley circulation: assessing NCEP/NCAR reanalysis and sparse in-situ estimates,” Climate Dynamics, vol. 15, no. 10, pp. 719–735, 1999.
[19]
G. Gastineau, L. Li, and H. Le Treut, “The Hadley and Walker circulation changes in global warming conditions described by idealized atmospheric simulations,” Journal of Climate, vol. 22, no. 14, pp. 3993–4013, 2009.
[20]
P. D. Sardeshmukh and B. J. Hoskins, “The generation of global rotational flow by steady idealized tropical divergence,” Journal of the Atmospheric Sciences, vol. 45, no. 7, pp. 1228–1251, 1988.
[21]
I. Simmonds and E. P. Lim, “Biases in the calculation of Southern Hemisphere mean baroclinic eddy growth rate,” Geophysical Research Letters, vol. 36, no. 1, Article ID L01707, 2009.
[22]
M. H. Shimizu and I. Cavalcanti, “Variability patterns of Rossby wave source,” Climate Dynamics, vol. 37, no. 3-4, pp. 441–454, 2011.
[23]
P. D. Sardeshmukh and B. J. Hoskins, “Spatial smoothing on the sphere,” Monthly Weather Review, vol. 112, pp. 2524–2529, 1984.
[24]
B. J. Hoskins, “Representation of the earth topography using spherical harmonics,” Monthly Weather Review, vol. 108, no. 1, pp. 111–115, 1980.
[25]
A. J. Simmons, “The forcing of stationary wave motion by tropical diabatic heating,” Quarterly Journal Royal Meteorological Society, vol. 108, no. 457, pp. 503–534, 1982.
[26]
P. J. Webster and J. R. Holton, “Cross-equatorial response to middle-latitude forcing in a zonally varying basic state,” Journal of the Atmospheric Sciences, vol. 39, no. 4, pp. 722–733, 1982.
[27]
D. J. Karoly, “Rossby wave propagation in a barotropic atmosphere,” Dynamics of Atmospheres and Oceans, vol. 7, no. 2, pp. 111–125, 1983.
[28]
G. Branstator, “Horizontal energy propagation in a barotropic atmosphere with meridional and zonal structure,” Journal of the Atmospheric Sciences, vol. 40, no. 7, pp. 1689–1708, 1983.
[29]
K. Takaya and H. Nakamura, “A formulation of a phase-independent wave-activity flux for stationary and migratory quasigeostrophic eddies on a zonally varying basic flow,” Journal of the Atmospheric Sciences, vol. 58, no. 6, pp. 608–627, 2001.
[30]
R. A. Plumb, “On the three-dimensional propagation of stationary waves,” Journal of the Atmospheric Sciences, vol. 42, no. 3, pp. 217–229, 1985.
[31]
G. C. Tyrrell, D. J. Karoly, and J. L. Mcbride, “Links between tropical convection and variations of the extratropical circulation during TOGA COARE,” Journal of the Atmospheric Sciences, vol. 53, no. 18, pp. 2735–2748, 1996.
[32]
K. E. Trenberth, G. W. Branstator, D. Karoly, A. Kumar, N.-C. Lau, and C. Ropelewski, “Progress during TOGA in understanding and modeling global teleconnections associated with tropical sea surface temperatures,” Journal of Geophysical Research C, vol. 103, no. 7, pp. 14291–14324, 1998.
[33]
X.-W. Quan, H. F. Diaz, and M. P. Hoerling, “Change in the tropical Hadley cell since 1950,” in The Hadley Circulation: Present, Past and Future, H. F. Diaz and R. S. Bradley, Eds., pp. 85–120, Kluwer Academic, 2005.
[34]
F. Jin and B. J. Hoskins, “The direct response to tropical heating in a baroclinic atmosphere,” Journal of the Atmospheric Sciences, vol. 52, no. 3, pp. 307–319, 1995.
[35]
A. C. V. Freitas and V. Brahmananda Rao, “Multidecadal and interannual changes of stationary Rossby waves,” Quarterly Journal of the Royal Meteorological Society, vol. 137, no. 661, pp. 2157–2173, 2011.
