Summer circulation patterns related to the upper tropospheric vortices over the Tropical South Atlantic

Kayano, Mary Toshie; Ferreira, Nelson Jesus; Ramírez, Maria Cleofé Valverde

doi:10.1007/bf01029693

Cited by 10 publications

(8 citation statements)

References 17 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Further, the presence of a trough over the North Atlantic as one of the characteristic features for the formation of the vortex was noted by Ramírez et al (1999). The vortex considered in this study exhibits a strong westward tilt with latitude, which can also be seen in the second EOF mode obtained by Kayano et al (1997). From the above discussion, it can be said that the vortex considered in the study is a typical and a representative case.…”

Section: Discussionmentioning

confidence: 69%

“…It has to be recognized that the changes in the large-scale embedding flow before the cyclonic vortex formation as found in the present case, such as the development and intensification of a ridge to the southeast of the Bolivian high and intensification of the South Atlantic trough, are also noted in earlier studies based on a single case study (Kousky and Gan 1981) or based on a large number of cases and using statistical techniques (Kayano et al 1997;Ramírez et al 1999). Further, the presence of a trough over the North Atlantic as one of the characteristic features for the formation of the vortex was noted by Ramírez et al (1999).…”

Section: Discussionmentioning

confidence: 74%

“…This implies that the strong tilt of the vortex developed subsequently. A preferred mode with its center close to the northeast Brazil coast, as obtained by Kayano et al (1997) from EOF analysis using 200-hPa daily filtered vorticity anomalies for 10 summers, also shows a NW-SE tilt. The N-S elongated vortex implies a stronger associated meridional motion compared to the zonal motion, which is in agreement with the observations.…”

Section: A Average Structure Of the Vortexmentioning

confidence: 99%

See 2 more Smart Citations

Structure and Evolution of the Large-Scale Flow and an Embedded Upper-Tropospheric Cyclonic Vortex over Northeast Brazil

Mishra¹,

Rao²,

Gan³

2001

Mon. Wea. Rev.

View full text Add to dashboard Cite

Horizontal structure and evolution of large-scale flow and an embedded synoptic-scale cyclonic vortex over northeast Brazil as separate systems and dynamical interaction between them are studied at 200 hPa. A quasistationary cyclonic vortex with its average position at 10ЊS and 35ЊW that formed and remained active during 5-10 January 1993 is selected for the investigation. The evolution of large-scale flow in the prevortex period 1-4 January is also explored. An efficient and effective scale separation technique is developed and used to separate the large-scale flow and embedded synoptic-scale vortex.It is shown that a strong positive shear zone developed in the latitude domain 17.5Њ-7.5ЊS, within the South Atlantic trough region before the vortex formation. The shear zone has a characteristic meridional (zonal) scale of 1000 km (3000 km) and satisfies strongly the necessary condition for barotropic instability. It is identified that the development of a strong shear zone is associated with the intensification of a Bolivian anticyclone and associated ridge and their eastward shift, and intensification of the South Atlantic trough, east-west orientation of the Atlantic trough, and the presence of a transient trough over the equatorial Atlantic Ocean.The average structure of vortex including zonal and meridional characteristic scales is computed from the synoptic bandpass flow. The vortex is identified as a nonlinear wave packet with an average zonal wavelength of 2750 km and it is confined to a latitude belt of about 17.5Њ. The vortex shows a strong westward tilt with latitude; the convergence zone is located to its southwest and it is a weak cold cored system. Maximum cyclonic vorticity of the vortex is Ϫ3.24 ϫ 10 Ϫ5 s Ϫ1 , which is comparable to the value for embedding flow. The momentum transports due to the vortex, large-scale eddy, and the vortex-large-scale eddy interaction are computed. It is found that the vortex and vortex-large-scale eddy westerly momentum transports are southward, down the gradient of embedding zonal flow, and their divergence (convergence) is located over the latitudes of large scale westerlies (easterlies). The sensible heat transports are weak. It is noted that the vortex-large-scale flow interaction leads to the weakening of the shear zone and restoration of the large circulation features to their January 1993 mean configuration, which have undergone significant deviation during the prevortex period. The signature of vortex-large-scale interaction is also seen in the evolution of dynamical parameters y and n 2 q (square of refractive index parameter).

show abstract

Section: Discussionmentioning

confidence: 69%

Section: Discussionmentioning

confidence: 74%

Section: A Average Structure Of the Vortexmentioning

confidence: 99%

See 1 more Smart Citation

Structure and Evolution of the Large-Scale Flow and an Embedded Upper-Tropospheric Cyclonic Vortex over Northeast Brazil

Mishra¹,

Rao²,

Gan³

2001

Mon. Wea. Rev.

View full text Add to dashboard Cite

show abstract

“…They exhibit a pronounced southeast-northrvest tilt with latitude. The wavelength associated rvith the initial stage of cyclonic vortex is around 3500 km (Kayano et al 1997;Kousky, and Gan 1981). The convective activity is observed mainly away from the vortgx center and particularly ahead of it, that is, ro its rvest.…”

Section: R379mentioning

confidence: 99%

Genesis of the Northeast Brazil Upper-Tropospheric Cyclonic Vortex: A Primitive Equation Barotropic Instability Study

Mishra

Rao

Franchito

2007

Journal of the Atmospheric Sciences

View full text Add to dashboard Cite

ABSTIìAgTThe primitive equation barotropic unstable tinear normal modes arc computed using an eigenvaluc approach for daily latitudinal profiles of zonat florv in the upper-tropospheric tãyer of l0G-350 hpa before and aftcr formation of cyclonic vortices during January 1993 and November 2001 off the coast of noÍtheâst Brazil' The s'ave kinetic energy equation for rr-and umotion is presented. Equarions arc derived to isolate the contribution of divergence and other dynamical processes in the movement anct grorvth of unslable modes. Numerical accuracy and physical nature of unstable modes are tested.In a short span of 2-3 days, prior to formation of vortices, a progressive and a sharp intensificâtion of the basic flow shear zone and its barotropic instabitity are seen rvith time. The horizontaistructure, momentum transport, and zonal and mcridional scales of the most unslable normalized wave aÍe obtained ancl compared rvith the vortex extracted from the 200-hPa observed rvinds.using a bandpass smoother. A close agreenÌent is foundbetseen them. It is shorvn that the zonal and mèridional scaleì ofthe preferred rvave are related to the lenglh scale of lhe shear zone. The rvale is confined to the shcar zone and its maximum amplitude is located at the latitude of maximunr F -frrr. The role of divergence in the movement antl growth of the rvave is investigated. The energctics of thsúnstable \\ave r.-anà umotion is computed, and it is inferred lhat'the eneÍgy source for the grorvth ofrvave rr-(rr) motion is the energy converiion (rvork done by pressure force), rvhich lies in the shear zone, It is emphasized that a deeper insight regarding the genesis of the cyclonic voÍtex can be gained on the basis of stability analy'sis of daily obsen'ed zonal flow profiles, rvhich may not be possible usirlg idealized or mean profiles-An exilanation for nonmanifestation oi the instability in ihe montilly mean flow is provided. r379 formed in the month of January and generally no vortex is observed during the rvinter (May-September). ïre monihly frequency (number of vortex days in a month) during the summer is 2.4 (22 days).They originate mainly in the 200-300-hPa layer and are observed in the area 20"-10oS, 45'-25"W. Furthermore, the vortices have a cold core at 300 hPa and have an average westward speed of about 4-6 m s-1. They exhibit a pronounced southeast-northrvest tilt with latitude. The wavelength associated rvith the initial stage of cyclonic vortex is around 3500 km (Kayano et al. 1997; Kousky, and Gan 1981). The convective activity is observed mainly away from the vortgx center and particularly ahead of it, that is, ro its rvest. Mishra et al. (2001, hereafter MRG) studied the evolution of large-scale florv and an embedded cyclonic vortex at 200 hPa. They noted the follorving: (a) the development of a strong shear zone before vortex formation; (b) a strong barotropic interaction betrveen vortex and largc-scale flol; and (c) the zonal and meÌ\tISHRA ET AL. IntroducÍionDuring the summer season of the Southern Hemisphere (Dece...

show abstract

“…In addition, precipitation over some parts of the Amazon can be influenced by the North Atlantic High and the Tropical Atlantic sea-surface temperature (Costa & Foley 1999). The precipitation regime over the Amazon is mainly modulated by the Inter-Tropical Convergence Zone (ITCZ), the South Atlantic Convergence Zone (SACZ) and the Bolivian High (Kodama 1992, Nobre & Shukla 1996, Kayano et al 1997.…”

Section: Introductionmentioning

confidence: 99%

Diurnal cycle of rainfall over the Brazilian Amazon

Angelis¹,

McGregor

Kidd

2004

Clim. Res.

View full text Add to dashboard Cite

The rainfall characteristics over the Brazilian Amazon were analysed using 3 yr of 3 h data from 24 rain gauges. During this period, areas in the eastern sector experienced up to 22% of rainy hours, while those in the southern sector recorded up to 7%. In the northern Amazon, rain tends to occur during the night, while in southern, central and central-western Amazon it occurs mainly in the afternoon. In contrast, over the eastern Amazon, rain occurs late at night and early in the morning. Harmonic analysis revealed an increase in the phase of the first harmonic phase from eastern towards central Amazon, suggesting that the rain propagates in that direction. The amplitude of the first and second harmonics revealed the existence of a relatively dry area inland about 500 km from the Atlantic coast. This area seems to be the limit for the inland penetration of systems originating at the coast. The phase of the first harmonic revealed small differences between the diurnal cycles of rainfall during the wet and dry seasons, suggesting that there is no difference between low-level circulations in either season. KEY WORDS: Amazon · Diurnal cycle · Rainfall · Precipitation · Rain gauge Resale or republication not permitted without written consent of the publisherClim Res 26: [139][140][141][142][143][144][145][146][147][148][149] 2004 noon, from about 15:00 to 19:00 h LST (Dai 2001). The phase of convective activity over land in the South and Central Americas, South and Central Africa, India and Borneo is generally from late afternoon to evening (Houze et al. 1981, Hendon & Woodberry 1993, Yang & Slingo 2001. Specifically over the eastern coast of the Amazon, it has been found that peaks of rainfall tend to occur at 05:00 h LST in Marajó Island and at 17:00 h LST in Belém (Kousky 1980). In the central Amazon, near the convergence between the Amazonas and Negro rivers and over the Reserva Florestal Ducke, located at 25 km from Manaus, peaks of precipitation occur at 12:00 and 15:00 h LST, respectively (Lloyd 1990, Cutrim et al. 2000.Despite the low rain-gauge density over the Amazon Basin, the pluviometers in that area are sufficient to allow evaluation of some rainfall characteristics and also to be very useful as ground truth for satellite applications. The main purpose of the present study is to analyse 3 yr of previously unavailable rain-gauge data over the Brazilian Amazon so as to increase knowledge of the diurnal variations of rainfall over this area. DATA AND ANALYSIS METHODThe nature of the diurnal rainfall cycle was established using harmonic analysis, which yields information about the amplitude and phase (timing) of the peak in a time series. The methodology followed is that outlined by Wilks (1995). Accordingly, rainfall is modelled at time t in a series y by the harmonic function:where y is the mean of the series, n is the period, C is the amplitude, φ is the phase and k is the harmonic number. The amplitude C is estimated by:(2) where A 1 = 2/n × Σy t cos(2πt/n) (3)The phase can then be derived...

show abstract

Summer circulation patterns related to the upper tropospheric vortices over the Tropical South Atlantic

Cited by 10 publications

References 17 publications

Structure and Evolution of the Large-Scale Flow and an Embedded Upper-Tropospheric Cyclonic Vortex over Northeast Brazil

Structure and Evolution of the Large-Scale Flow and an Embedded Upper-Tropospheric Cyclonic Vortex over Northeast Brazil

Genesis of the Northeast Brazil Upper-Tropospheric Cyclonic Vortex: A Primitive Equation Barotropic Instability Study

Diurnal cycle of rainfall over the Brazilian Amazon

Contact Info

Product

Resources

About