查看更多>>摘要：Electron density enhancement caused by electromagnetic radiation emitted during a solar X-ray flare has the potential to increase high frequency (HF; 3-30 MHz) absorption in the dayside D-region ionosphere, impacting shortwave radio signals by reducing the signal strength, a phenomenon commonly referred to as shortwave fadeout. Data-based optimization of a simple absorption model is performed incorporating solar X-ray flux data and 30 MHz riometer data from stations distributed across Canada. In a single event study the data-based optimization model is shown to overestimate absorption by 1% for the duration of an X2.1 solar X-ray flare. This corrects an underestimation by the NOAA D-region Absorption Prediction (D-RAP) model. In a statistical study, based on 87 events, data-based optimization performed on an event-by-event basis showed excellent overall agreement between measured and modelled data: the Pearson correlation coefficient was R = 0.88, and the slope of the best-fit line to the data was m = 0.91. A generalized model was developed using data from all 87 events collectively. Although good agreement was found between the measured and modelled data sets, correlation and slope were slightly reduced to R = 0.75 and m = 0.80. Model accuracy is characterized by prediction efficiency (PE) which peaked at PE = 0.78 for the event-by-event evaluation and PE = 0.48 for the collective data set. The results of this study highlight the advantages of data-based optimization in modelling absorption due to shortwave fadeout.
查看更多>>摘要：An extreme rainstorm event (1056.7 mm/day) along the South China coast in summer 2018 is investigated using WRF model. We focused on the effects of single-moment WSM6/7 and double-moment WDM6/7 microphysics schemes on the extreme precipitation. (1) The precipitation area, rain band movements and changes in hourly rainfall intensity could be robustly simulated in the 4 experiments. The performance of each scheme varied across different grades of precipitation. WDM7 scheme simulated precipitation extremes and hourly rain intensity that were closest to observations and produced relatively higher scores for light rain; WSM6 scheme had relatively higher scores for moderate rain; and WSM7 scheme showed higher scores for heavy rain and rainstorm. (2) Compared with the single-moment scheme, the double-moment scheme showed higher cloud water and hail mixing ratios. There was no significant difference in cloud water and snow mixing ratios. (3) Schemes incorporating the hail particles showed a larger cloud water mixing ratio but a smaller graupel mixing ratio. Incorporating hail particles caused an increase in simulated precipitation intensity and smaller simulation errors. (4) The increase in graupel mixing ratios was correspondent to the three precipitation peaks. The temporal evolutions of graupel, hail and snow mixing ratios are similar to that of precipitation, with the peak of cloud water mixing ratio appearing earlier than that of precipitation and the peak of ice mixing ratio appearing later than that of precipitation.
查看更多>>摘要：We present a formulation for calculating the electric field from the ground to the lower boundary of the ionosphere that is based on an analytical solution to Poisson's equation in three dimensions, combined with a numerical solution to the equation of charge continuity/conservation. This formulation allows one to follow the spatial and temporal evolution of the distribution of free charges and the electric field in the atmosphere and thus predict areas of possible sprite inception in the mesosphere in a quasi-electrostatic fashion for any thundercloud charge distribution. The main advantages of this formulation are: (1) for a given spatial resolution, the analytical solution to Poisson's equation is more numerically stable and accurate than a numerical solution to Poisson's equation that includes finite differencing in space; (2) unlike a numerical solution to Poisson's equation that includes finite differencing in space, the numerical stability is insensitive to the choice of spatial resolution; (3) no artificial side boundary condition need be applied; (4) no symmetry, cylindrical or otherwise, of the charge distributions nor the electric field distributions need be prescribed; and (5) the computation is readily parallelizable on multiple processors. The main limitation of the present formulation is that the electric field based on the electrostatic potential with upper and lower boundary conditions needs to be calculated for each charge in the domain, such that the larger the number of charges, the slower the computation. We explore the sensitivity of the formulation to its parameters, in order to elucidate its feasibility for performing simulations for a variety of thunderstorm charge distributions in 3D, and we demonstrate its utility in investigating the evolution of the area of possible sprite inception in cases of consecutive lightning discharges that are separated from one another in space as well as in time. In all of the simulations in the present study, the ambient electrical conductivity varies in space but is independent of time. However, as we discuss, our formulation can also accommodate a time dependent conductivity profile.
Matsumoto, HarukaSvensmark, HenrikEnghoff, Martin Bodker
13页
查看更多>>摘要：This study examines the relationship between cosmic rays and clouds during Forbush decreases (FDs) to understand the cause-effect relationships between cloud microphysics, cloud condensation nuclei (CCN), and ionisation in the atmosphere. The results of a Monte Carlo analysis of cloud parameters during FDs, which were obtained using newly calibrated satellite data (Pathfinder Atmospheres Extended (PATMOS-x)) from 1978 to 2018, show the connections between some cloud parameters and FDs. For context, FD is the event where the number of cosmic rays arriving in the atmosphere decreases and recovers over several days. Other studies have shown that FDs impacted the cloud fraction, aerosol optical depth, CCN, water content, and cloud effective radius (r(eff)) in the atmosphere. Using the Monte Carlo analysis, nine atmospheric parameters from the dataset were evaluated and exhibited a significant response to FDs. Each added FD event (after the first event) reduces the noise, but only the strongest events add a significant signal (exceptionally when the 2nd and 5th rank FD data are added, the signal/noise ration dropped due to a change in the satellite version). We found that cloud fraction shows statistically significant signals following FDs at an achieved significance level of 0.33%. Cloud emissivity also showed highly significant signals from the analysis; however, these cannot be classified as physical causes of FDs since the response starts a week before the FDs. In contrast, the cloud optical depth, integrated total cloud water over the entire column, and r(eff) did not show any significant signals in the frameworks of the applied methods. The top of the atmosphere brightness temperatures (TABTs) at nominal wavelengths of 3.75, 11.0, and 12.0 mu m were analysed again along with surface BTs and showed significant signals. The estimated changes in the BT were determined using a radiative transfer model (Fu-Liou model) and showed consistent results with the observed changes in cloud parameters during FD events. Among the analysed several atmospheric/cloud/aerosol parameters, cloud fraction and TABT at nominal wavelengths of 3.75, 11.0, and 12.0 mu m are the only parameters depicting a statistically significant and correct-phase response to FDs.
查看更多>>摘要：Based on the high-frequency measurement data of three-dimensional wind speed and temperature during the haze period, the turbulent motion and its influence on the heat transport process were revealed. Our results show that the results of the initial and decay stages of the haze event are qualitatively consistent with the results during the sunny days, and are close quantitatively. The difference of turbulence between haze events and sunny days is mainly reflected in the development stage of haze events. For fluctuations with a period greater than 1 h, with the development of the haze event, the large-scale fluctuation value of vertical wind speed increases, which can reach 0.65 m/s; the peak value of temperature fluctuation decreases; turbulence intensity of vertical wind speed, shear stress and vertical heat flux increase; the outward interaction events dominates the turbulent motion and the upward transportation of hot air. For fluctuations with a period of less than 1 h, as the PM10 concentration increases, the vertical heat flux gradually decreases; the diurnal changes of the shear stress will change qualitatively, that is, the shear stress first increases and then decreases; on the whole, the number of outward interaction events and inward interaction events in the development stage of haze events is greater than the number of ejection events and sweeps events; quantitatively, the flux peaks of events corresponds to upward transportation of high-speed hot air, upward transports of high-speed cold air, downward transport of high-speed hot air and downward transports of high-speed cold air decrease with the development of haze events. Therefore, the turbulent motion of different scales needs to be considered in the study of the haze events.
查看更多>>摘要：The study of the properties and variations of planetary boundaries such as magnetosheaths and bow shocks is an important subject for magnetospheric dynamics and interaction with solar wind. The identification of these boundaries is important for those studies. Thus, the Haar wavelet decomposition technique is used to detect the planetary magnetosphere boundaries and discontinuities. We use the magnetometer data from the CASSINI and MESSENGER spacecraft to identify the abrupt changes in the magnetic field when the spacecraft crossed the magnetospheric bow shocks and magnetopauses of Saturn and Mercury, respectively. The methodology based on variance obtained by scale and edge identifications was shown to be a simple tool to perform this task. The results confirm that the Haar transform can efficiently identify the planetary magnetosphere boundaries char-acterized by the abrupt magnetic field changes. Due to this wavelet function to be a discrete function it promotes the abrupt and sharp identification of the boundaries. It is suggested that this technique can be applied to detect the planetary boundaries as well as the discontinuities such as the shock waves in the interplanetary space.
NSTL
Elsevier