ALBERT

Description: We use the evolutionary population synthesis method to investigate the statistical properties of the wind-fed neutron-star (NS) compact ( P orb 〈 10 d) high-mass X-ray binaries (HMXBs) in our Galaxy, based on different spin-down models. Model 1 assumes that the surrounding material is treated as forming a quasi-static atmosphere. Model 2 assumes that the characteristic velocity of matter and the typical Alfvén velocity of material in the magnetospheric boundary layer are comparable to the sound speed in the external medium. We find that the spin-down rate in the supersonic propeller phase in either model 1 or model 2 is too low to produce the observed number of compact HMXBs. Model 3 assumes that the infalling material is ejected with the corotation velocity at the magnetospheric radius when the magnetospheric radius is larger than the corotation radius. Model 4 uses simple integration of the magnetic torque over the magnetosphere. Both models 3 and 4 have a larger spin down rate than that given by model 1 or 2. We also find that models 3 and 4 can predict a reasonable number of observed wind-fed NS compact HMXBs. By comparing our calculated results with the observed particular distributions of wind-fed NS compact HMXBs in a P s versus P orb diagram, we find that the subsonic propeller phase may not exist at all. However, the spin-down rates in models 3 and 4 both seem reasonable to produce the observed distribution of wind-fed NS compact HMXBs in the P s versus P orb diagram. We cannot find which spin-down rate seems more reasonable from our calculations.

Description: Whole Atmosphere Community Climate Model (WACCM) simulations are used to investigate solar and lunar tide changes in the mesosphere and lower thermosphere (MLT) that occur in response to sudden stratosphere warmings (SSWs). The average tidal response is demonstrated based on 23 moderate to strong Northern Hemisphere SSWs. The migrating semidiurnal lunar tide is enhanced globally during SSWs, with the largest enhancements (∼60–70%) occurring at mid to high latitudes in the Northern Hemisphere. Enhancements in the migrating solar semidiurnal tide (SW2) also occur up to an altitude of 120 km. Above this altitude, the SW2 decreases in response to SSWs. The SW2 enhancements are 40–50%, making them smaller in a relative sense than the enhancements in the migrating semidiurnal lunar tide. Changes in nonmigrating solar tides are, on average, generally small and the only nonmigrating tides that exhibit changes greater than 20% are the diurnal tide with zonal wave number 0 (D0) and the westward propagating semidiurnal tide with zonal wave number 1 (SW1). D0 is decreased by ∼20–30% at low latitudes, while SW1 exhibits a similar magnitude enhancement at mid to high latitudes in both hemispheres. The tidal changes are attributed to a combination of changes in the zonal mean zonal winds, changes in ozone forcing of the SW2, and nonlinear planetary wave-tide interactions. We further investigate the influence of the lunar tide enhancements on generating perturbations in the low latitude ionosphere during SSWs by using the WACCM-X thermosphere to drive an ionosphere-electrodynamics model. For both solar maximum and solar minimum simulations, the changes in the equatorial vertical plasma drift velocity are similar to observations when the lunar tide is included in the simulations. However, when the lunar tide is removed from the simulations, the low latitude ionosphere response to SSWs is unclear and the characteristic behavior of the low latitude ionosphere perturbations that is seen in observations is no longer apparent. Our results thus indicate the importance of variability in the lunar tide during SSWs, especially for the coupling between SSWs and perturbations in the low latitude ionosphere.

Description: Author(s): Y.-C. Wen, K.-J. Wang, H.-H. Chang, J.-Y. Luo, C.-C. Shen, H.-L. Liu, C.-K. Sun, M.-J. Wang, and M.-K. Wu [Phys. Rev. Lett. 109, 089902] Published Tue Aug 21, 2012

Description: Author(s): H. L. Liu, F. R. Xu, and P. M. Walker Total Routhian surface calculations have been performed to investigate rapidly rotating transfermium nuclei, the heaviest nuclei accessible by detailed spectroscopy experiments. The observed fast alignment in 252 No and slow alignment in 254 No are well reproduced by the calculations incorporating hig... [Phys. Rev. C 86, 011301] Published Fri Jul 06, 2012

Description: The atmospheric semidiurnal lunar tide is added to the Whole Atmosphere Community Climate Model (WACCM) through inclusion of an additional forcing mechanism. The simulated climatology of the semidiurnal lunar tide in surface pressure and zonal and meridional winds in the mesosphere and lower thermosphere (MLT) is presented. Prior observations and modeling results demonstrate characteristic seasonal and latitudinal variability of the semidiurnal lunar tide in surface pressure, and the WACCM reproduces these features. In the MLT, the WACCM simulations reveal a primarily semiannual variation with maxima near December and June solstice. The peak amplitudes in the MLT zonal and meridional winds are ∼5–10 ms−1, and occur at mid to high latitudes in the summer hemisphere. We have further compared the WACCM simulation results in the MLT with those from the Global Scale Wave Model (GSWM). The overall latitude and seasonal variations are consistent between these two models. However, the GSWM peak amplitudes are ∼2–3 times larger than those in the WACCM. This is thought to be related to deficiencies in the GSWM and not the WACCM simulations. With the exception of smaller amplitudes during Northern Hemisphere summer months, the WACCM simulations of the semidiurnal lunar tide in the MLT are also shown to be generally consistent with prior observations and modeling results. The reduced amplitudes in the WACCM simulations during Northern Hemisphere summer months are thought to be related to the influence of the cold-pole bias in WACCM on the propagation of the lunar tide during these months.

Description: To investigate day-to-day variability in the mesosphere and lower thermosphere (MLT), an idealized simulation of a six-day westward propagating zonal wave number-1 planetary wave is performed using the National Center for Atmospheric Research (NCAR) Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM). The six-day planetary wave introduces a six-day periodicity in the zonal mean atmosphere, migrating and nonmigrating tides, as well as in secondary waves that are produced by nonlinear planetary wave-tide interactions. We have further used the linear Global Scale Wave Model (GSWM) to isolate the effect of how the day-to-day changes in zonal mean zonal winds may influence tides in the MLT. The most significant changes are observed in the migrating diurnal tide (DW1), eastward propagating nonmigrating tides with zonal wave numbers-2 and -3 (DE2 and DE3), and a 20 hr eastward propagating wave with zonal wave number-2 (20E2). Because we have included the lower atmospheric source of nonmigrating tides, DE2 and DE3 are present with relatively large amplitudes in the MLT, even in the absence of planetary wave forcing. The 20E2 wave is produced by the nonlinear interaction between the DE3 and the six-day planetary wave, and its large amplitude indicates the importance of including the realistic spectra of nonmigrating tides in numerical simulations of planetary waves. The GSWM simulations reveal that the DW1 is not significantly influenced by the changes in the zonal mean winds. We thus conclude that the DW1 changes are driven by a combination of changes due to nonlinear interaction with the six-day planetary wave as well as changes due to zonal asymmetries that result from the six-day planetary wave. The six-day planetary wave induced changes in zonal mean zonal winds lead to a general reduction in the amplitude of DE2 and DE3, and introduce a slight periodic behavior in these tides. The effect of changing zonal mean zonal winds appears to be the primary driver of the changes in the DE2. However, for DE3, although the changes that can be attributed to zonal mean zonal wind variability are not insignificant, the primary driver of the DE3 perturbations appears to be the nonlinear interaction with the six-day planetary wave. Last, we demonstrate that the day-to-day changes in the DE3 introduce similar day-to-day changes in the daytime wave number-4 longitude structure in the low-latitude ionosphere. These results indicate that short-term variability in the low-latitude ionosphere is likely to be driven by similar short-term variability in nonmigrating tides in the MLT.

Description: It is very important to predict the shock arrival times (SATs) at Earth for space weather practice. In this paper we use the energy of soft X-ray during solar flare events to help predict the SATs at Earth. We combine the soft X-ray energy and SAT prediction models previously developed by researchers to obtain two new methods. By testing the methods with the total of 585 solar flare events following the generation of a metric type II radio burst during the Solar Cycle 23 from September 1997 to December 2006, we find that the predictions of SATs at Earth could be improved by significantly increasing PODn, the proportion of events without shock detection that were correctly forecast. PODn represents a method's ability in forecasting the solar flare events without shocks arriving at the Earth, which is important for operational predictions.

Description: Author(s): H. L. Liu, F. R. Xu, P. M. Walker, and C. A. Bertulani Using, for the first time, configuration-constrained potential-energy-surface calculations with the inclusion of β_{6} deformation, we find remarkable effects of the high-order deformation on the high-K isomers in ^{254} No, the focus of recent spectroscopy experiments on superheavy nuclei. For sha... [Phys. Rev. C 83, 011303] Published Mon Jan 24, 2011

Description: Author(s): C. Xu, H. Hua, X. Q. Li, J. Meng, Z. H. Li, F. R. Xu, Y. Shi, H. L. Liu, S. Q. Zhang, Z. Y. Li, L. H. Zhu, X. G. Wu, G. S. Li, C. Y. He, S. G. Zhou, S. Y. Wang, Y. L. Ye, D. X. Jiang, T. Zheng, J. L. Lou, L. Y. Ma, E. H. Wang, Y. Y. Cheng, and C. He High-spin states in ^{157} Yb have been populated in the ^{144} Sm( ^{16} O,3n) ^{157} Yb fusion-evaporation reaction at a beam energy of 85 MeV. Two rotational bands built on the νf_{7/2} and νh_{9/2} intrinsic states, respectively, have been established for the first time. The newly observed νf... [Phys. Rev. C 83, 014318] Published Fri Jan 28, 2011

Description: Abstract The mesopause, a boundary between mesosphere and thermosphere with the coldest atmospheric temperature, is formed mainly by the combining effects of radiative cooling of CO2, and the vertical adiabatic flow in the upper atmosphere. A continuous multidecade (1990‐2018) nocturnal temperature data base of an advanced Na lidar, obtained at Fort Collins, CO (41°N, 105°W), and at Logan, UT (42°N, 112°W), provides an unprecedented opportunity to study the long‐term variations of this important atmospheric boundary. In this study, we categorize the lidar‐observed mesopause into two categories: the “high mesopause” (HM) above 97 km during nonsummer months, mainly formed through the radiative cooling, and the “low mesopause” (LM) below 92 km during nonwinter months, generated mostly by the adiabatic cooling. These lidar observations reveal a cooling trend of more than 2 K/decade in absolute mesopause temperature since 1990, along with a decreasing trend in mesopause height: The HM is moving downward at a speed of ~ 450 ± 90 m/decade, while the LM has a slower downward trend of ~ 130 ± 160 m/decade. However, since 2000, while the height trend (‐ 470 ± 160 m/decade for the HM and 150 ± 290 m/decade for the LM) is consistent, the temperature trend becomes statistically insignificant (‐ 0.2 ± 0.7 K/decade and ‐1 ± 0.9 K/decade for the HM and the LM, respectively). A long‐term study by Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM‐X) also indicated the similar mesopause changes, mostly caused by stratosphere‐lower mesosphere cooling and contraction.