Energetics of southeastern Pacific cut-off lows

Quart J Royal Meteoro Soc

et al. 2021

Cut‐Off Lows (COLs) in the Southern Hemisphere and the mechanisms involved in their development are investigated in detail using the eddy kinetic energy (EKE) budget applied to data from the ERA‐Interim reanalysis. This approach considers the most important processes that are typical for the evolution of midlatitude disturbances such as the baroclinic (BRC) and barotropic (BRT) conversions, and the ageostrophic flux convergence (AFC), known as downstream development. Composites of the volume‐integrated EKE and its components are evaluated based on the 200 most intense SH COLs (>98th percentile) observed in a 36‐year period. Results show that the AFC together with the BRC conversion are the most important contributors to the EKE growth for the COLs, characterizing the downstream baroclinic development. The AFC plays an important role in genesis and intensification phases of the COLs, while the BRC conversion is important for the system maintenance. The dissipation of the COLs occurs due to dispersive fluxes (ageostrophic flux divergence) together with other processes not directly computed in the EKE equation, such as friction and latent heat release which are problematic in reanalysis datasets. The BRT conversion contributes negatively to the COL development by transferring EKE to the zonal flow kinetic energy, though this is not enough to dampen the intensification. Regional differences were found in the energetics, indicating that COLs originating upstream of the continents are clearly dominated by ageostrophic fluxes, while the systems over the Australian region are mostly driven by baroclinic processes.

Section: Introductionsupporting

confidence: 58%

Section: Introductionmentioning

confidence: 98%

Contributions of downstream baroclinic development to strong Southern Hemisphere cut‐off lows

Pinheiro

Hodges

Quart J Royal Meteoro Soc

et al. 2021

“…(, ), we prefer the energetics analysis that was recently applied by Müller et al . () for tropical frost events over South America and Gan and Piva (, ) for cut‐off lows, because this equation separates the energy transport and leaves a transport term that can be directly associated with downstream development (DSD) proposed by Orlanski and Katzfey ()

\begin{matrix} \frac{\partial EKE}{\partial t} = - \nabla . \overset{true\to}{V} EKE - \nabla . \overset{true\to}{V_{a}^{'}} ϕ^{'} - ω^{'} α^{'} \\ - \overset{true\to}{V^{'}} . (\overset{true\to}{V_{3}^{'}} . \nabla_{3}) \overset{true¯}{\overset{V}{true}} + \overset{true\to}{V^{'}} . \overset{true¯}{(\overset{true\to}{V_{3}^{'}} . \nabla_{3}) \overset{true\to}{V^{'}}} \\ - \frac{\partial}{\partial p} ω EKE - \frac{\partial}{\partial p} ω^{'} ϕ^{'} + RES \end{matrix}

…”

Section: Event Selection Criteria Data and Methodologymentioning

confidence: 99%

Energetics of wave propagation leading to frost events in South America: extratropical latitudes

Müller

Atmospheric Science Letters

Piva

2017

Self Cite

The dynamics of wave propagation and energy associated with frosts in extratropical versus tropical South American latitudes is studied. A double wave train propagates through the southern hemisphere following the polar and subtropical jets. If, in the previous day, both trains coincide in phase over the southeast Pacific (southwest Atlantic) Oceans, it will contribute to generate generalized frosts (strong frosts) at extratropical (tropical) latitudes, not affecting tropical (extratropical) latitudes given the wave train zonal propagation. The vertically averaged eddy kinetic energy composites show three maxima associated with those trains over the South Pacific Ocean and South American region.

“…A energética desses casos foi obtida através da equação de K do distúrbio (K' À Eq. (1)) desenvolvida por Orlanski e Katzfey (1991) e modificada por Chang (2000), a qual tem sido utilizada em vários estudos (Gan e Piva, 2013, 2016Müller et al 2015Müller et al , 2017 na América do Sul.…”

Section: Dados E Metodologiaunclassified

“…A energética pode ser obtida por diferentes formulações como a de Lorenz (1967) e a Orlanski e Katzfey (1991). Os estudos de Gan e Rao (1999), Pezza et al (2010Pezza et al ( , 2014, Dias Pinto e da Rocha (2011), Dias Pinto et al (2013) e Rosa et al (2013) são exemplos da utilização da formulação de Lorenz (1967) em sistemas que atuam na América do Sul, enquanto os estudos de Gan e Piva (2013, 2016, para vórtices ciclônicos em altos níveis sobre o oceano Pacífico Sul, e de Müller el al. (2015Müller el al.…”

Section: Introductionunclassified

Ciclones em Superfície nas Latitudes Austrais. Parte III: Energética

Ferreira

Costa

et al. 2020

Rev. bras. meteorol.

Self Cite

Resumo Esse estudo tem como objetivo apresentar a análise da energética de quatro casos de ciclones em latitudes austrais, sendo dois extratropicais (um do tipo Bjerknes e Solberg e o outro do tipo Shapiro e Keyser), um tropical e um subtropical, a fim de complementar o trabalho “Ciclones em Superfície nas Latitudes Austrais: Parte II Estudo de Casos”. Para tanto, utilizou-se a equação da energia cinética do distúrbio desenvolvida por Orlanski e Katzfey, pois ela contempla os principais mecanismos para a formação e dissipação dos sistemas transientes, isto é, as instabilidades baroclínica e a barotrópica, além do desenvolvimento corrente abaixo. A análise da energética mostra que o termo de conversão baroclínica foi o mais importante durante o ciclo de vida dos quatro ciclones estudados, já o termo barotrópico foi pequeno. Por outro lado, o termo de desenvolvimento corrente abaixo, conhecido como convergência do fluxo ageostrófico, atuou negativamente em todos os casos, exportando energia cinética para fora da região do ciclone.