查看更多>>摘要：Rapid changes in the tropospheric circulation features associated with the overhead passage of the Gaja cyclonic system over the 205 MHz Stratosphere Troposphere wind profiler radar observations at Kochi (10.03? N, 76.33 E), India, have been studied. The severe cyclonic system formed in the southeast Indian Peninsular region weakened into a depression after landfall near the Tamil Nadu coast. On 16th November 2018, the cyclonic system crossed the Western Ghats and travelled westward at 33 knots over the ST radar site at Kochi in the evening. Later it reached the Arabian Sea and intensified again into a severe cyclone. Continuous observations of the vertical structure of the wind pattern at 4-min intervals from the wind profiler radar have been examined. The impact of the transit of the cyclonic system extends up to a height of 13 km in the atmosphere. The vertical distribution of turbulent kinetic energy in the atmosphere indicates a sudden disruption in the tropospheric levels at the time of storm passage. The cyclonic system traversed over the Western Ghats positioned at an altitude of 2500 m. It crossed the radar site at the mean sea level after passing a horizontal distance of 100 km. The abrupt changes in the topographical conditions generate atmospheric gravity waves in the leeward side of the Western Ghats, as observed from the ST radar, are presented. During the period, changes in surface parameters were evaluated using co-located automatic weather station (AWS) data. Satellite information and Doppler weather radar observations from Kochi have also supplemented the investigation.
查看更多>>摘要：The electromagnetic field generated by lightning is measured at extremely low frequencies (< 100 Hz) in many places on Earth. These measurements are called Schumann resonance (SR) measurements. From SR measurements the location and intensity of global lightning activity can be estimated by applying an inversion algorithm. In this paper, we present an inversion approach based on singular value decomposition (SVD) for this problem and we describe some quality features of the applied inversion technique. The inversion algorithm is tested on synthetic data and the reliability of the obtained results is examined based on the described quality features. Our synthetic tests confirm that the described quality features are very useful in determining the reliability of inversion results. An important conclusion from the synthetic tests is that the quality of the inversion is not adversely affected by incorrect assumptions about the location of the lightning sources.
查看更多>>摘要：To obtain information about Earth disturbances to the ionosphere of the atmosphere, a Software Defined Radio (SDR) Earth Imager was constructed at the Dominion Radio Astrophysical Observatory (DRAO). This imager used radio waves reflected from the Earth's ionization layer to phase image waves on/in the ionosphere. Two sets of waves were found, one having a constant frequency and another having a large spike. The constant frequency waves represent a continuously active ionospheric disturbance such as a power generating station. The large spike waves were randomly occurring outliers. Candidates for the spike waves are lightning strikes and/or earthquakes. Having the capability to detect these waves opens up the possibility of measuring the power, energy and location of their disturbance.
查看更多>>摘要：The atmospheric turbulence characteristics such as energy dissipation rate (epsilon), eddy diffusivity (K), and refractive index structure parameter (Cn2), which are inevitable to understand the vertical mixing and transport of pollutants, momentum, and energy, are least explored over the Himalayan region owing to the unavailability of observations. Here, we investigate the characteristics of turbulence in the troposphere (TS) and lower stratosphere (LS) using Thorpe's method for intense radiosonde measurements made during July 2011 to March 2012, from a central Himalayan site Manora Peak (79.5 degrees E, 29.4 degrees N, and 1936 m AMSL). Findings reveal that the energy dissipation rate (log epsilon), and eddy diffusivity (log K), are right-skewed with central mean values about -3.90 (-3.30) m2s- 3 and -0.19 (-0.24) m2s- 1, in the TS (LS) region. However, Cn2 follows the right (left) -skewed distribution with the mean value of -16.9 (-19) m- 2/3, in the TS (LS). The mean values of inner scale (lo) and buoyancy scale (LB) are 0.051 (0.104) m and 84.62 (8.34) m in the TS (LS). The monthly and seasonal variations of these parameters were also examined and presented. The mean profiles of log epsilon show the lowest dissipation rate (-4.5 m2s-3) during the post-monsoon season and constant dissipation rate (--4 m2s-3) below 5 km in winter, however, mixing coefficient log K shows a constant variation (--0.01 m2s-1) above 8 km. Larger buoyancy scales (>100 m) are observed in the altitude range of 8-14 km during moist and lighter monsoon circulations. This study extricates the effect of orography-induced local circulations that controls turbulence intensity in the lower troposphere, especially in the weak mean flow conditions. This study essentially provides the quantified vertical distribution of the atmospheric parameters associated with turbulence and to be utilized for understanding the related physical processes.
查看更多>>摘要：We present a modified spectrographic global survey method to split the cosmic ray variations into components of the interplanetary, geomagnetospheric, and atmospheric origin from ground-based observations of the cosmic ray intensity. We show a possibility to use all the available suite of ground-based instrumentation recording cosmic rays (global network of the neutron monitors located at different locations and altitudes, ground-and underground-based muon telescopes, etc.) for such studies without involving the data from aerologic atmospheric sounding. As a demonstration of the method functionality, we provide the calculation results for the variations in the isotropic flux, pitch angle anisotropy of primary cosmic rays in the interplanetary space, changes in the planetary system of geomagnetic cutoff rigidities for every observational hour, as well as the atmosphere temperature above the point of observation of cosmic ray charged components for selected time intervals.
查看更多>>摘要：The daily values of the E-KL field and indices of magnetic activity PC, AL and Dst were used to verify stability of relationships between these parameters in course of 23rd and 24th solar cycles. The results of analysis demonstrate that the mean level of correlation between the E-KL field and PC index remains in range R = 0.85-0.90 over 24 years. During the solar maximum epochs (2008, 2015) the correlation between E-KL and PC reduced down to R = 0.75, the decrease being related to solar protons events (SPE), which strongly affect the ionospheric conductivity in polar caps. In the course of both cycles the daily AL index well correlated with PC index (R = 0.93) and with E-KL field (R = 0.83); correlation of daily Dst index with PC and EKL values was much worse (R = 0.72 and 0.64, correspondingly), the correlation being independent of solar activity epochs and cycles. The PC indices in northern (PCN) and southern (PCS) indices hemispheres demonstrate the evident seasonal variation; the PCsummer index is commonly larger than the PCwinter index, but PCwinter index better correlates with E-KL field. The conclusion is made that relationships between the E-KL field, PC index, and the magnetic disturbance indices AL and Dst remained valid in course of 23rd and 24th solar cycles and, therefore, the calibrating coefficients, determining these relationships, are not affected by solar activity.
Guo, Z. -X.Yang, J. -Y.Dunlop, M. W.Cao, J. -B....
9页
查看更多>>摘要：Convolutional neural networks (CNNs) in deep learning enable the extraction of features in image data. Through the multi-layer superposition of a convolutional neural network, we can better capture the essential characteristics of different auroral subclasses and further classify auroral images in detail. Because the auroral morphological features often present abstract characteristics, our study compares different CNN architectures and different layering in order to test the best neural network model for mesoscale aurora classification. Although the classification models and subclasses used by us are both more complex, the highest F1 score of aurora classification of the test set reaches 99.6% (ResNet-50), which performs best comparing with previous works. Our classification models work also quite well when applied to an independent auroral image sequence, declaring our approach can automatically select images of various mesoscale auroral forms using CNNs, and allow the time sequence of auroral evolution to be seen automatically through the mesoscale auroral feature recognitions.
查看更多>>摘要：Sea-effect snowfall is a special form of snow in the coastal areas of the Bohai Sea in China. However, a quantitative understanding of its water vapor and cloud microphysical mechanisms is still lacking. In this study, the Weather Research and Forecasting model version 4.0 with three microphysics schemes was employed to investigate a sea-effect snowstorm that occurred in the north of Shandong Peninsula on 9-10 January 2018. The simulated snowfall amount, temperature and humidity profiles, and radar reflectivity were in general agreement with the observations. The moisture budget revealed that the water vapor came completely from evaporation of the surface of Bohai Sea. The largest water vapor sink term was the moisture advection, followed by the deposition and condensation (accounting for only 15% of the sea surface evaporation). This phenomenon is analogous to heating water in a kettle and then the water vapor drifting away with the wind. In the main snowfall area, the total water vapor transport was positive (i.e., inflow) below the height of 1.5 km, and was almost zero above 3.0 km. The period of maximum moisture inflow in the low layer was about 30 min ahead of the maximum surface snowfall. In addition, the hydrometeor distributions in this sea-effect snowstorm were relatively simple compared to those in non-sea-effect snowstorm; the snow content was the most (0.09 g kg(-1)), followed by the supercooled cloud water (0.01 g kg(-1)), owing to the weak convection in it. Snow growth was dominated by the vapor deposition, and the process of rimming accounted for only 1/4 of the vapor deposition. The evidently weaker vapor condensation than vapor deposition is quite different from that in summertime heavy rainfall.
Moro, J.Silva, R. P.Nogueira, P. A. B.Chen, S. S....
9页
查看更多>>摘要：In this work, we observe for the first time the unusual pre-sunrise Equatorial Plasma Bubbles (EPBs) during a moderate geomagnetic storm recovery phase caused by the High-Speed Solar Wind Stream (HSS) on February 17, 2015, over the Brazilian sector. Therefore, this study aims to explain the generation mechanism of this uncommon event, which started at 08:00 UT on February 18, 2015. We used Multiple Global Navigation Satellite Systems (Multi-GNSS, GPS, and GLONASS) data to produce two-dimensional maps of the Rate Of TEC index (ROTI) that show EPB features elongated in magnetic meridians. Also, Digisonde data from Sa similar to o Luis (2.53 degrees S, 44.30 degrees W, dip angle: 8.57 degrees), Boa Vista (12.81 degrees N, 60.67 degrees W, dip angle: 33.71 degrees), and Campo Grande (20.44 degrees S, 54.64 degrees W, dip angle: 25.98 degrees), and magnetometer data at Sa similar to o Luis and Euse ' bio (3.89 degrees S, 38.45 degrees W, dip angle: 17.96 degrees). Our analysis shows that the unusual pre-sunrise plasma bubbles lasted longer after sunrise, around 1 h. Finally, we showed that these EPBs are likely driven by a disturbance wind dynamo effect, which helps to understand the role of the external factors in EPBs development.
Belov, A. A.Klimov, P. A.Kozelov, B. V.Barrillon, P....
8页
查看更多>>摘要：A new telescope-spectrometer was installed at Verkhnetulomsky observatory (68?36'N, 31?47'E) to supplement the data from all-sky cameras with measurements of the fine space-time structure of the auroral luminescence. The telescope uses 5 cm ultraviolet (UV) transparent lens as an optical system and a matrix of multi-anode photomultiplier tubes as a photo detector. The angular resolution of the telescope is 1.2? and the temporal resolution is 0.3 ms. The telescope observes a central part (20?) of the all-sky camera field of view (FOV). Description of both optical instruments and results of the first joint measurements are presented.
NSTL
Elsevier