Longitude

About: Longitude is a research topic. Over the lifetime, 2260 publications have been published within this topic receiving 54988 citations. The topic is also known as: angle of longitude.

Sudden stratospheric warming event signatures in daytime ExB drift velocities in the Peruvian and Philippine longitude sectors for January 2003 and 2004

Abstract: [1] This paper first describes the technique that has been developed to obtain realistic, daytime, vertical ExB drift velocities in the equatorial ionosphere using two ground-based magnetometers, one on the magnetic equator and the other located ±6°–9° away in latitude. This technique is then employed to study the unique ExB drift signatures associated with sudden stratospheric warming events (SSW) in both the Peruvian and Philippine longitude sectors, occurring in January 2003 and January 2004. It is found that the semidiurnal shaped signature first appears in the Peruvian sector and 3 days later appears in the Philippine sector. In both sectors, the ExB drift signature lasts for approximately 5 days.

On the Decades-Long Stability of the Interstellar Wind through the Solar System

Abstract: We have revisited the series of observations recently used to infer a temporal variation in the interstellar helium flow over the past forty years. Concerning the recent IBEX-Lo direct detection of helium neutrals, there are two types of precise and unambiguous measurements that do not rely on the exact response of the instrument: the count rate maxima as a function of the spin angle, which determines the ecliptic latitude of the flow, and the count rate maxima as a function of IBEX longitude, which determines a tight relationship between the ecliptic longitude of the flow and its velocity far from the Sun. These measurements provide parameters (and couples of parameters in the second case) that are remarkably similar to the canonical, old values. In contrast, the preferred choice of a lower velocity and higher longitude reported before from IBEX data is only based on the count rate variation (at each spin phase maximum) as a function of the satellite longitude, when drifting across the region of high fluxes. We have examined the consequences of dead-time counting effects and conclude that including them at a realistic level is sufficient to reconcile the data with the old parameters, calling for further investigations. We discuss the analyses of the STEREO pickup ion data and argue that the statistical method that has been preferred to infer the neutral flow longitude (instead of the more direct method based on the pickup ion maximum flux directions) is not appropriate. Moreover, transport effects may have been significant at the very weak solar activity level of 2007−2009, in which case the longitudes of the pickup ion maxima are only upper limits on the flow longitude. Finally, we found that using some flow longitude determinations based on UV glow data is not adequate. Based on this global study, and at variance with recent conclusions, we find no evidence for a temporal variability of the interstellar helium flow. This has implications for inner and outer heliosphere studies.

East-west differences in F-region electron density at midlatitude: Evidence from the Far East region

Abstract: The global configuration of the geomagnetic field shows that the maximum east-west difference in geomagnetic declination of northern middle latitude lies in the US region (similar to 32 degrees), which produces the significant ionospheric east-west coast difference in terms of total electron content first revealed by Zhang et al. (2011). For verification, it is valuable to investigate this feature over the Far East area, which also shows significant geomagnetic declination east-west gradient but smaller (similar to 15 degrees) than that of the US. The current study provides evidence of the longitudinal change supporting the thermospheric zonal wind mechanism by examining the climatology of peak electron density (NmF2), electron density (Ne) of different altitudes in the Far East regions with a longitude separation of up to 40-60 degrees based on ground ionosonde and space-based measurements. Although the east-west difference (R-ew) over the Far East area displays a clear diurnal variation similar to the US feature, that is negative R-ew (West Ne > East Ne) in the noon and positive at evening-night, the observational results reveal more differences including: (1) The noontime negative R-ew is most pronounced in April-June while in the US during February-March. Thus, for the late spring and summer period negative R-ew over the Far East region is more significant than that of the US. (2) The positive R-ew at night is much less evident than in the US, especially without winter enhancement. (3) The magnitude of negative R-ew tends to enhance toward solar maximum while in the US showing anticorrelation with the solar activity. The altitude distribution of pronounced negative difference (300-400 km) moves upward as the solar flux increases and hence produces the different solar activity dependence at different altitude. The result in the paper is not simply a comparison corresponding to the US results but raises some new features that are worth further studying and improve our current understanding of ionospheric longitude difference at midlatitude. Citation: Zhao, B., M. Wang, Y. Wang, Z. Ren, X. Yue, J. Zhu, W. Wan, B. Ning, J. Liu, and B. Xiong (2013), East-west differences in F-region electron density at midlatitude: Evidence from the Far East region, J. Geophys. Res. Space Physics, 118, 542-553, doi:10.1029/2012JA018235.