Convection and Dynamo in Newly Born Neutron Stars

To study properties of magnetohydrodynamic (MHD) convection and resultant dynamo activities in proto-neutron stars (PNSs), we construct a “PNS in a box” simulation model and solve the compressible MHD equation coupled with a nuclear equation of state (EOS) and simplified leptonic transport. As a demonstration, we apply it to two types of PNS model with different internal structures: a fully convective model and a spherical-shell convection model. By varying the spin rate of the models, the rotational dependence of convection and the dynamo that operate inside the PNS is investigated. We find that, as a consequence of turbulent transport by rotating stratified convection, large-scale structures of flow and thermodynamic fields are developed in all models. Depending on the spin rate and the depth of the convection zone, various profiles of the large-scale structures are obtained, which can be physically understood as steady-state solutions to the “mean-field” equation of motion. Additionally to those hydrodynamic structures, a large-scale magnetic component of  ( 10 15 ) G is also spontaneously organized in disordered tangled magnetic fields in all models. The higher the spin rate, the stronger the large-scale magnetic component grows. Intriguingly, as an overall trend, the fully convective models have a stronger large-scale magnetic component than that in the spherical-shell convection models. The deeper the convection zone extends, the larger the size of the convective eddies becomes. As a result, rotationally constrained convection seems to be more easily achieved in the fully convective model, resulting in a higher efficiency of the large-scale dynamo there. To gain a better understanding of the origin of the diversity of a neutron star’s magnetic field, we need to study the PNS dynamo in a wider parameter range.

Comments on “Global and Regional Entropy Production by Radiation Estimated from Satellite Observations”

A recent paper by Kato and Rose reports a negative correlation between the annual mean entropy production rate of the climate and the absorption of solar radiation in the CERES SYN1deg dataset, using the simplifying assumption that the system is steady in time. It is shown here, however, that when the nonsteady interannual storage of entropy is accounted for, the dataset instead implies a positive correlation; that is, global entropy production rates increase with solar absorption. Furthermore, this increase is consistent with the response demonstrated by an energy balance model and a radiative–convective model. To motivate this updated analysis, a detailed discussion of the conceptual relationship between entropy production, entropy storage, and entropy flows is provided. The storage-corrected estimate for the mean global rate of entropy production in the CERES dataset from all irreversible transfer processes is 81.9 mW m−2 K−1 and from only nonradiative processes is 55.2 mW m−2 K−1 (observations from March 2000 to February 2018).

A new convective model for the Maud Rise Polynya

<p>The Maud Rise Polynya, a large hole in the Antarctic sea-ice, was first observed in the 1970s and reappeared again in 2017. The general paradigm is that the polynya formed due to deep convection caused by static instability of the water column. There is, however, no consensus on the processes responsible for the initialisation of deep convection. Both atmospheric and oceanic processes have been suggested by observational and model studies. Deep convection is viewed as an irregular event caused by densification of the surface layer. Heat accumulation in the subsurface layer is also considered to be vital for the formation of the polynya. This study investigates the initiation of deep convection using a simple 1D convective model introduced by Martinson et al. (1981) which is further extended with a dynamical subsurface layer. This extended version of the model allows us to study the contribution of both surface- and subsurface forcing on the initiation of deep convection. Two model set-ups with different subsurface characteristics have been used: (1) with a constant subsurface layer; (2) with periodic subsurface accumulation of heat and/or salt. Model set-up 1 results in either one or no polynya events. This does not agree with observations, since multiple polynya events have been observed. Model set-up 2 results in in periodically returning polynyas with the same period as the subsurface accumulation. Therefore, model set-up 2 is able to again multiple events as observed. Adding noise to the simulations does not change the conclusions for both model set-ups. The results suggest that subsurface forcing is a dominant process in Maud Rise Polynya formation. Our results indicate that densification of the surface layer plays a much smaller role than previously assumed by various literature. Based on these results and previous studies, we suggest that subsurface processes govern both the initial formation and reccurrence of the Maud Rise Polynya.</p>

Avaliação de Parametrizações de Camada Limite Planetária do Modelo WRF na Costa Norte do Nordeste do Brasil

Resumo Este trabalho tem como objetivo avaliar duas simulações do modelo WRF que diferem em sua parametrização da Camada Limite Planetária (CLP). Foram utilizados dados de 72 radiossondas lançadas em Fortaleza (CE) entre 5 e 25 de Abril de 2011 nos horários sinóticos. A altura da CLP foi a variável avaliada e os valores observados, calculados pelo método do gradiente vertical da temperatura potencial, foram de 245±28 m para o período noturno e de 925±63 m para o período diurno. As parametrizações de CLP avaliadas foram Asymmetric Convective Model V2 e Mellor Yamada Nakanish and Niino 2.5. O desempenho destas foi avaliado por comparação estatística com dados observados, utilizando-se o Erro Médio Absoluto (EMA) e o índice refinado de concordância de Willmott (dr). Para a ACM2 obtiveram-se valores de EMA iguais a 282 m e 519 m e dr de 0,53 e 0,37, respectivamente, para os períodos noturno e diurno. Com MYNN2,5, foram encontrados valores de EMA entre 312 m e 266 m, com dr entre 0,59 e 0,56 para os períodos noturno ediurno, respectivamente. A parametrização MYNN2,5 mostrou-se mais eficiente, considerando ambas as métricas. No entanto, somente para 00UTC, a ACM2 apresentou melhor desempenho.

Impact of middle range energy electron precipitations on polar winter ozone losses

In this paper we present the study of polar winter atmospheric response to middle range energy electron precipitations. We analse the variability of the odd nitrogen group NOx, hydrogen group HOx in the polar wonter atmosphere and estimate the ozone (O3) depletion caused by the middle range energy electron precipitations. For the study we exploit 1-D radiative-convective model with interactive neutral and ion chemistry. Ionization rates induced by middle-energy electrons were taken from the CMIP6 (Coupled Model Intercomparison Project Phase 6) solar forcing dataset. The atmospheric response to ionization rates induced by middleenergy electrons during polar night consists of increase of mesospheric HOx by 0.1-0.4 ppbv and NOx by 10-90 ppbv driving ozone losses up to 5% over zonal band of about 750 NH.