The dawn−dusk asymmetry in mesosphere and lower thermosphere temperature disturbances during geomagnetic storms at high latitude

Utilizing observations by the Sounding of the Atmosphere using Broadband Emission Radiometry(SABER)instrument,we quantitatively assessed the dawn-dusk asymmetry in temperature disturbances within the high-latitude mesosphere and lower thermosphere(MLT)during the main phase of geomagnetic storms in this study.An analysis of five geomagnetic superstorm events indicated that during the main phase,negative temperature disturbances were more prevalent on the dawn side than on the dusk side in the high-latitude MLT region.Results of a statistical analysis of 54 geomagnetic storm events also revealed a notable disparity in temperature disturbances between the dawn and dusk sides.At high latitudes,38.2%of the observational points on the dawn side exhibited negative temperature disturbances(less than−5 K),whereas on the dusk side,this percentage was only 29.5%.In contrast,at mid-latitudes,these proportions were 34.1%and 36.5%,respectively,showing no significant difference.We also conducted a statistical analysis of temperature disturbances at different altitudes,which revealed an increase in the proportion of warming disturbances with altitude.Conversely,the proportion of cooling disturbances initially rose with altitude,reaching a peak around 105 km,and subsequently decreased.These temperature disturbance differences could be explained by the day-night asymmetry in vertical wind disturbances during storm conditions.

Acoustic Purcell effect induced by quasibound state in the continuum

We study theoretically and experimentally the acoustic Purcell effect induced by quasi-bound states in the continuum(quasiBICs).A theoretical framework describing the acoustic Purcell effect of a resonant system is developed based on the system’s radiative and dissipative factors,which reveals the critical emission condition for achieving optimum Purcell factors.We show that the quasiBICs contribute to highly confined acoustic field and bring about greatly enhanced acoustic emission,leading to strong Purcell effect.Our concept is demonstrated via two coupled resonators supporting a Friedrich-Wintgen quasiBIC,and the theoretical results are validated by the experiments observing emission enhancement of the sound source by nearly two orders of magnitude.Our work bridges the gap between the acoustic Purcell effect and acoustic BICs essential for enhanced wave-matter interaction and acoustic emission,which may contribute to the research of high-intensity sound sources,high-quality-factor acoustic devices and nonlinear acoustics.

Emissions and noise mitigation through use of electric motorcycles

Gasoline-powered motorcycles contribute disproportionately to traffic noise and emissions,so motorcycle electrification merits investigation.Recent advances in battery efficiency allow electric motorcycles(EMCs)to join electric cars and bicycles as a viable consumer option.This study quantifies noise and emissions using both simulations and experimental data,examines the factors that make motorcycles big offender and uses popular EMC makes and models to estimate the costs and benefits of electrification in the USA.Motorcycles produce more CO,CH4,NOx,HC and particulate matter per vehicle-mile travelled than passenger vehicles.Due to limited regulation of motorcycles and weak enforcement,the perceived noise level of motorcycles exceeds that of most other vehicles,being roughly double those of automobiles at speeds of over 30 mph and surpassing even those of medium trucks and buses at speeds of over 50 mph,at which point motorcycles exceeds the 80 dBA US standard limit.Electrification can resolve such issues,although range limitations and high prices are presently a barrier to widespread adoption.In order to realize these environmental benefits,it is important that electrification occurs with a corresponding shift away from coal as an energy source.Stricter emission regulations and stronger enforcement of existing prohibitions on certain forms of customization could also reduce the outlier status of gasoline-powered motorcycles.