In this paper, we obtain a CR version Li–Yau type gradient estimate for positive solutions of the CR heat equation on closed Sasakian manifolds. As its applications, we derive the Harnack inequality ...and upper bound estimate for the heat kernel. Finally, we obtain Perelman-type entropy formula for closed Sasakian manifolds.
Previous works have shown that coseismic ionospheric disturbances (CIDs) after the tsunamigenic 2011 Tohoku earthquake (Tohoku EQ, Mw9.1) covered a vast area and were observed thousands of kilometers ...away from the epicenter. For the purpose of making a comprehensive comparison between powerful oceanic and inland EQs, we conduct a retrospective investigation of CIDs and geomagnetic responses to the 2008 Wenchuan EQ (Mw7.9) using a combination of techniques, total electron content, HF Doppler, and ground magnetometer. It is the very first study to present CIDs recorded by different techniques at co‐located sites and profiled with regard to changes of both ionospheric plasma and current (geomagnetic field) simultaneously. The integrated observation also shows that (1) in the Wenchuan case, most of the ionospheric and geomagnetic disturbances were observed within 1000 km distance which is far less than the Tohoku case; (2) two groups of CIDs were found with maximum amplitudes in the direction of azimuth 150° and 135°, respectively; and (3) the geomagnetic changes were only registered by three magnetometers located to the east and southeast of the epicenter. All the facts indicate that the main directional lobe of Wenchuan EQ energy propagation is to southeast and perpendicular to the direction of the fault rupture, but this kind of directivity is not that distinct in the Tohoku case. We suggest that the different fault slip (inland or submarine) affecting the way of couplings of lithosphere with atmosphere may contribute to the discrepancies between the two events.
Key Points
Ionospheric and geomagnetic changes caused by a major inland earthquake
Strong directivity of CID distribution related to fault rupture direction
Different features in CIDs of inland case compared with oceanic case
The 2015 St. Patrick's Day geomagnetic storm with SYM‐H value of −233 nT is an extreme space weather event in the current 24th solar cycle. In this work, we investigated the main mechanisms of the ...profound ionospheric disturbances over equatorial and low latitudes in the Asian‐Australian sector and the American sector during this super storm event. The results reveal that the disturbed electric fields, which comprise penetration electric fields (PEFs) and disturbance dynamo electric fields (DDEFs), play a decisive role in the ionospheric storm effects in low latitude and equatorial regions. PEFs occur on 17 March in both the American sector and the Asian‐Australian sector. The effects of DDEFs are also remarkable in the two longitudinal sectors. Both the DDEFs and PEFs show the notable local time dependence, which causes the sector differences in the characteristics of the disturbed electric fields. This differences would further lead to the sector differences in the low‐latitude ionospheric response during this storm. The negative storm effects caused by the long‐duration DDEFs are intense over the Asian‐Australian sector, while the repeated elevations of hmF2 and the equatorial ionization anomaly intensifications caused by the multiple strong PEFs are more distinctive over the American sector. Especially, the storm time F3 layer features are caught on 17 March in the American equatorial region, proving the effects of the multiple strong eastward PEFs.
Key Points
The disturbed electric fields play a decisive role in the ionospheric responses in low latitude and equatorial regions during the storm
Penetration electric fields and disturbance dynamo electric fields occur in both the Asian‐Australian sector and the American sector
The salient storm time F3 layer is observed in the American equatorial region but not in the East Asian sector
On 12 May 2008 at 0628 UT a major earthquake Ms = 8.0 struck Wenchuan County (31.0°N, 103.4°E) in southwest China. The maximum ionospheric electron density at F2 peak (NmF2) recorded an unusual large ...enhancement during the afternoon‐sunset sector by the Chinese ionosondes over Wuhan (30.5°N, 114.4°E) and Xiamen (24.4°N, 123.9°E), which are close to the earthquake epicenter. An averaged increase at these two stations is about 2 times on a geomagnetic quiet day, 9 May (Kp ≤ 2), 3 days prior to the earthquake, relative to the median value of 1–12 May, whereas the increase was much less significant over Yamagawa (31.2°N, 130.6°E) and Okinawa (26.7°N, 128.2°E) in Japan. Combining the data from the network of 58 global positioning system receivers around China and the global ionospheric map, the variations of the total electron content reveal the region where enhancement persisted for a long period to be within longitudes 90°–130°E. Our results suggest that this abnormal enhancement is most possibly a seismo‐ionospheric signature.
Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) electron density profiles are used to investigate the nighttime midlatitude ionospheric trough (MIT). We find that at ...midnight the longitudinally deepest MIT occurs to the west of the geomagnetic pole in both the Northern and Southern Hemispheres during the equinox seasons and local summer. The deepest MIT could be ascribable to the enhanced depletion caused by horizontal neutral wind. In the early evening, the eastward neutral wind prevails in the midlatitude F region, which blows the plasma downward where the declination is eastward in the Northern Hemisphere but westward in the Southern Hemisphere, both lying to the west of the geomagnetic pole. The downward drift would enhance the plasma depletion for more molecular composition at lower altitude. In addition, we find for the first time that the location of nighttime MIT minimum oscillated with a periodicity of 9 days and an amplitude of about 1°–1.5° geomagnetic latitude during 2007–2008, associated with the recurrent high‐speed solar wind. Our results shed new light on the empirical description and numerical simulation of MIT.
Key Points
Deepest MIT occurs to the west of the geomagnetic pole in the N and S Hemispheres
The deepest MIT could be ascribed to the enhanced depletion by horizontal wind
MIT is found to oscillate periodically at 9 days about 2 to 3 deg from peak to peak
In the development of Sanya Incoherent Scatter Radar (SYISR), which is a major scientific instrument project founded by the National Natural Science Foundation of China (NSFC), we established a ...prototype system of 8 subarrays (named SYISR-8 hereafter), including 256 transceiver modules totally, beginning in July 2018 to verify the functions of the radar. Based on SYISR-8, we configured the system to detect the meteor echo with high range resolution. During a continuous observation interval of 16 h, 55 meteor echo events were found. Among these events, 34 cases were head echoes, 18 cases were specular trail echoes, and 3 cases were head echo and nonspecular trail echo concurrent events. We have observed 2 potential direct meteoroid fragmentation cases of all 55 meteor events. It demonstrates that potential direct observation of meteoroid fragmentation could be observed by a relatively small aperture and power using pulse compression processing. However, the occurrence ratio of meteoroid fragmentation in our experiment is approximately 6%, which is considerably lower than that observed in previous studies, which needs further investigation.
•Meteor echoes observation results by SYISR-8 are demonstrated in a high range resolution mode.•The SYISR-8 was configured to detect meteoroid with 37.5m resolution through pulse compression technique.•Two potential direct meteoroid fragmentation cases were observed for the first time to our knowledge using the SYISR-8.•Typical meteor echoes could be observed by a high range resolution radar with relatively small aperture and power.
The plasma lines observed by Sanya incoherent scatter radar (SYISR) are dependent on the enhancement of Langmuir waves due to superthermal photoelectrons generated by solar EUV radiation. The plasma ...line power spectrum can be obtained using long-pulse and alternating-code transmission signals during the period from sunrise to noon almost every day. For the power spectrum of the long pulse, the CLEAN algorithm that has been applied in this field is used to verify the feasibility of this method for SYISR in only a few cases. However, it is difficult to deal with alternating code with such a low SNR using the general deconvolution method. The irreversible-migration filtering (IMF) method has been developed to separate signal noise from the measurements of the alternating code. Some experimental results from the SYISR measurements validate the excellent performance of the IMF method for alternating code. Additionally, an example observation of the electron density with a high time and range resolution is derived. The results show that plasma line detection can be a powerful new observational capability for SYISR as an ionospheric experimental mode for ionospheric calibration, when possible, which can be simultaneously measured with the ion line for constant radar calibration in the standard fitting of the ion line.
Using TIME3D-IGGCAS model, we simulated the east–west differences in F-region peak electron density (NmF2) in the Far East mid-latitude region near the longitudinal sectors with very clear zonal ...variations of geomagnetic declination, and mainly analyzed the influence of the geomagnetic field configuration on the east–west differences. We found that, after removing the longitudinal variations of neutral parameters, TIME3D-IGGCAS can better represent the observed relative east–west difference (
R
ew
) features.
R
ew
is mainly negative (West NmF2 > East NmF2) at noon and positive (East NmF2 > West NmF2) at evening–night. The magnitude of daytime negative
R
ew
is weaker in winter and stronger in summer, and the daytime
R
ew
shows two negative peaks around two equinoxes. With the increasing solar flux level, the magnitude of
R
ew
mainly becomes larger, and the two daytime negative peaks slightly shift to June Solstice. With the decreasing geographical latitude,
R
ew
mainly becomes positive, and the two daytime negative peaks slightly shift to June Solstice. Our simulation also suggested that the thermospheric zonal wind plays an important role in the formation of the ionospheric east–west differences in the Far East mid-latitude region. The observed solar activity dependency of the ionospheric EW differences may be driven primarily by corresponding zonal wind changes with solar activity, whereas the observed latitudinal dependency of the differences is associated with primarily zonal wind and secondarily meridional wind latitudinal variations.
Sudden stratospheric warming (SSW) events in Northern Hemisphere winter atmosphere play a significant effect on large ionospheric disturbances. Nevertheless, the SSW effects on small‐scale structure ...in ionosphere, that is, the ionospheric F layer irregularities, are generally lack of understanding. This work carefully studied the equatorial F layer scintillation during the SSW event extending from 4 January to 5 February in 2013 by using the data of COSMIC/FORMOSAT‐3 (a Constellation Observing System for Meteorology, Ionosphere, and Climate mission). The occurrence rate of ionospheric F layer scintillation was found to be apparently decreased by about 30% during the SSW period. This phenomenon was obviously seen in American sector (90°W–0°) and African sector (0°–90°E). Another prominent feature was the ~0.5 local time hour delay of maximum scintillation occurrence rate associated with the suppression of equatorial F layer irregularities in the first 2 hr after the sunset during the SSW event in January 2013.
Key Points
It is the first time to study the response of small scale structure in ionosphere during SSW by COSMIC data sets
The occurrence rate of ionospheric F‐layer scintillation weakened by about 30% during the January 2013 SSW event
The weakening is obvious in American and African sectors, not obvious in other sectors, which are attributed to low scintillation in winter
In this paper, an ionospheric electron density reanalysis algorithm was used to generate global optimized electron density during the 17–18 March 2013 geomagnetic storm by assimilating ~10 low Earth ...orbit satellites based and ~450 ground global navigation satellite system receiver‐based total electron content into a background ionospheric model. The reanalyzed electron density could identify the large‐scale ionospheric features quite well during storm time, including the storm‐enhanced density, the positive ionospheric storm effect during the initial and main phases, and the negative ionospheric storm effect during the recovery phase. The simulations from the Thermosphere Ionosphere Electrodynamics General Circulation Model can reproduce similar large‐scale ionospheric disturbances as seen in the reanalysis results. Both the reanalysis and simulations show long‐lasting (>17 h) daytime negative storm effect over the Asia sector as well as hemispheric asymmetry during the recovery phase. Detailed analysis of the Global Ultraviolet Imager‐derived O/N2 ratio and model simulations indicate that the polar ward meridional wind disturbance, the downward E × B drift disturbance and O/N2 depletion might be responsible for the negative storm effect. The hemispheric asymmetry is mainly caused by the geomagnetic field line configuration, which could cause hemispheric asymmetry in the O/N2 depletion.
Key Points
Global ionospheric storm effects during 17 March 2013 geomagnetic storm were studied based on the data assimilation and TIEGCM simulation
Both the reanalysis and simulations show long‐lasting and hemispheric asymmetry negative storm effect during the recovery phase
The wind, E x B drift disturbance, and hemispheric asymmetry O/N2 depletion might be responsible for the negative storm effect
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