The explosive eruption of the Hunga‐Tonga volcano in the southwest Pacific at 0415UT on 15 January 2022 triggered gigantic atmospheric disturbances with surface air pressure waves propagating around the globe in Lamb mode. In space, concentric traveling ionosphere disturbances (CTIDs) are also observed as a manifestation of air pressure waves in New Zealand ∼0500UT and Australia ∼0630UT. As soon as the air pressure waves reached central Australia ∼0800UT, conjugate CTIDs appeared almost simultaneously in the northern hemispheres through interhemispheric coupling, much earlier than the arrival of the surface air pressure waves to Japan after 1100UT. Combining observations over Australia and Japan between 0800 and 1000UT, both direct and conjugate CTIDs show similar horizontal phase velocities of 320–390 m/s, matching with the dispersion relation of Lamb mode. The arrival of atmospheric Lamb wave to Japan later created in situ CTIDs showing the same Lamb mode characteristics as the earlier conjugate CTIDs.

[1] The ionosphere responses to a solar flare observed by using ground-based receivers of the global positioning system (GPS) are investigated in this paper. Two quantities, the total electron content (TEC) and its time rate of change (rTEC), can be derived from the receivers. The theoretical studies show that the rTEC is related to the frequency deviation of the GPS signals. Meanwhile, worldwide ground-based GPS receivers are employed to derive the TEC and associated rTEC to monitor the ionospheric solar flare effect on 14 July (Bastille Day) 2000. It is found that ionospheric solar flare effects can be observed from predawn to postdusk regions, and the most pronounced signatures appear in the midday area. The agreement between theoretical predications and observations demonstrates that the TEC is suitable to monitor the overall variations of flare radiations while the rTEC is capable to detect sudden changes in the flare radiations.

[1] At 17:47 UT on 20 September 1999, a large earthquake of magnitude M w 7.6 struck the central Taiwan near a small town of Chi-Chi. The ground-based receivers of the global positioning system (GPS) in the Taiwan area detected coseismic ionospheric disturbances (CIDs) in the total electron content (TEC) triggered by the Chi-Chi earthquake. When the CIDs travel away from the origin on the Earth surface and then propagate into the ionosphere, their amplitudes and periods generally become smaller and longer, respectively. Moreover, two global grid searches, adapting the ray-tracing and the beam-forming techniques, have been used to analyze the observed GPS TEC. We have not only estimated the average speed of the CIDs propagating in the atmosphere and ionosphere but also determined the location of CID origin on the Earth surface by using the two techniques. The results show that the observed CIDs result from shock-acoustic waves triggered by sudden and large vertical motions of the Chi-Chi earthquake.

Structure and propagation of equatorial Kelvin waves during May 2001 and December 2002 are observed from the temperature profiles in the upper troposphere and the lower stratosphere using CHAMP and SAC-C GPS radio occultation data. Kelvin waves derived from temperature fluctuations characterize eastward phase propagation in time-longitude section and eastward phase tilts with height in altitude-longitude section between 10 and 30 km. The phase progression spans the range indicating the continuity of Kelvin waves from the upper troposphere to the lower stratosphere. Results show that near the tropopause, Kelvin waves fluctuate temperature by 2 K in general, with wave periods of 12.5-14 days for zonal wave number 1 and 9.3-11.0 days for wave number 2, and vertical wavelengths of 7.6-8.5 km in 2001 and of 4.4-5.8 km in 2002.

It has been predicted that the Moon's shadow, the cooling region, sweeping over the Earth's atmosphere with a supersonic speed could trigger bow waves since 1970. The longest total solar eclipse within next hundred years occurring on 22 July 2009 sweeps over the Eastern Asia region during the noontime period. An analysis of the Hilbert‐Huang transform (HHT) is applied to study ionospheric TEC (total electron content) derived from ground‐based GPS receivers in Taiwan and Japan. We not only find the feature of the predicted bow wave but also the stern wave on the equator side of the eclipse path, as well as the stern wake right behind the Moon's shadow boat. The bow and stern waves are formed by acoustic gravity waves of periods about 3 and/or 5 minutes traveling equatorward with a phase speed of about 100 m/s in the ionosphere.

Propagation of the initial ionospheric total electron content (TEC) disturbances generated by the 2011 off the Pacific coast of Tohoku Earthquake at 05:46:23 UT on March 11, 2011, was investigated with ground-based Global Positioning System (GPS) receivers in the east-Asian region. It was found that the initial ionospheric disturbance formed a zonal wave front after the earthquake occurrence. Four zonal wave fronts of this initial ionospheric disturbance were observed to travel southward from Japan to Taiwan with a velocity of about 1,000-1,700 m/s. This study further found that the direction of the wave vector rotated from the south-southwest to the south-southeast as it traveled from Japan to Taiwan. The meridional propagation of the coseismic ionospheric disturbances is consistent with those observed after previous intense earthquakes. The temporal evolutions of initial ionospheric disturbances, after the earthquake, near the epicenter was observed in two-dimensions. The directivity of the disturbances was caused by a geomagnetic field effect.

[1] For the past decade, the paucity of ionospheric observations has made it almost impossible to reconstruct the three-dimensional structures of global ionospheric electron density. The Formosa Satellite-3/Constellation Observing System for Meteorology, Ionosphere and Climate (FORMOSAT-3/COSMIC, F3/C) constellation has provided ionospheric electron density profiles with high vertical resolution through radio occultation measurements. Slated for deployment starting in 2016, the FORMOSAT-7/COSMIC-2 (F7/ C2) constellation will further provide more than 4 times the number of the F3/C occultation soundings. An observing system simulation experiment is conducted to determine the impact of F7/C2 on ionospheric weather monitoring. The results first show that the F7/C2 observations can reconstruct 3-D ionospheric structure with a data accumulation period of 1 h, which can advance studies of small spatial/temporal scale variation/signatures in the ionosphere. Comparing to assimilation results of F3/C, the assimilation system significantly reduces the error arising in the models and observations after assimilating synthetic observations of F7/C2. During this observing system simulation experiment period, the averaged root-mean-square error percentage for the results of F7/C2 is about 4.4%, lower than that of F3/C 7.3%. Furthermore, even with an assimilation window of less than 60 min, the F7/C2 RMS errors still yield reliable values compared to the F3/C results. This paper represents a major advance in ionospheric weather monitoring for the future mission.

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