On the basis of the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC)‐measured fluctuations in the signal‐to‐noise ratio and excess phase of the GPS signal piercing through ionospheric sporadic E (Es) layers, the general morphologies of these layers are presented for the period from July 2006 to May 2011. It is found that the latitudinal variation in the Es layer occurrence is substantially geomagnetically controlled, most frequent in the summer hemisphere within the geomagnetic latitude region between 10° and 70° and very rare in the geomagnetic equatorial zone. Model simulations show that the summer maximum (winter minimum) in the Es layer occurrence is very likely attributed to the convergence of the Fe⁺ concentration flux driven by the neutral wind. In addition to seasonal and spatial distributions, the height‐time variations in the Es layer occurrence in the midlatitude (>30°) region in summer and spring are primarily dominated by the semidiurnal tides, which start to appear at local time around 6 and 18 h in the height range 110–120 km and gradually descend at a rate of about 0.9–1.6 km/h. In the low‐latitude (<30°) region, the diurnal tide dominates. The Horizontal Wind Model (HWM07) indicates that the height‐time distribution of Es layers at middle latitude (30°–60°) is highly coincident with the zonal neutral wind shear. However, Es layer occurrences in low‐latitude and equatorial regions do not correlate well with the zonal wind shear.

The gamma drop size distribution (DSD) has been widely used in the meteorological community for years to model observed DSD. It has been found that the relation between the slope (Λ) and shape (μ) parameters of the gamma DSD can be empirically described by a polynomial of second degree. In this article, on the basis of disdrometer-measured DSDs from seven independent precipitation events associated with different weather systems, an empirical μ–Λ relation that is slightly different from those reported by other scientists is obtained by best fitting a quadratic polynomial to observed data. In addition to the empirical relation, a μ–Λ relation is derived based on theoretical relations between gamma DSD moments and Λ and μ. It is shown that the derived μ–Λ relation is independent of the order of the moment of the gamma DSD. The key factor dominating the μ–Λ relation is the ratio of the number density parameter N(Dm) to total number density of the raindrop M0, where Dm is the mean diameter of the DSD. It is further shown that the skewness and the variance of the DSD determine the magnitude of the ratio N(Dm)/M0 that governs the slope of the μ–Λ relation. A comparison between the derived and the empirical μ–Λ relations shows that their behaviors are very similar, especially for large rainfall rates characterized by smaller Λ and μ values. Moreover, the ratio N(Dm)/M0 bears a weak relation to the rainfall rate R. Nevertheless, the square of the ratio M0/N(Dm) is closely related to the ratio R/M0 and their relation can also be described by a second-degree polynomial. Considering this property, the authors examine the validity of the various μ–Λ relations by simulating the relations between R/M0 and [M0/N(Dm)]2. A comparison between observed and simulated results shows that the relation generated from the derived μ–Λ relation bears the best resemblance to the observed one in both magnitude and shape.

An annular solar eclipse swept over Taiwan in the early morning on 21 May 2012. This provides an excellent opportunity to study ionospheric response to the solar eclipse mainly due to photochemical effects. Local ground‐based Global Positioning System receivers, an ionosonde, high frequency‐continue wave Doppler sounding systems, and very low frequency receivers are used to observe ionospheric eclipse signatures. These multiinstrument observations show that the extreme total electron content (TEC) depression lags the maximum obscuration by about 5–20 min, while the Doppler frequency shift decreases and increases (i.e., the ionosphere ascends and descends) during first contact‐maximum obscuration and maximum obscuration‐last contact, respectively. The ionosonde data well agree with the TEC and Doppler frequency shift observations. The results show that the extreme TEC depression lag (i.e., delay time) being inversely proportional to the associated maximum obscuration confirms that the photochemical process is essential in Taiwan during the 21 May 2012 annular solar eclipse. A theoretical derivation is proposed for the first time to explain the delay time due to pure photochemical process during solar eclipses.

[1] With interferometry measurements made with Chung‐Li 52 MHz VHF radar, characteristics of layer‐type and clump‐type plasma structures of 3‐m field‐aligned irregularities are investigated for the first time. Long‐term statistics show that the thickness and the zonal extent of the layer‐type plasma structures are in the ranges of approximately 0.1–4 km and 5–28 km, respectively. However, the vertical and zonal extents of the clump‐type plasma structure are comparable with each other, ranging from 2 to 12 km. These features clearly imply that the cross sections of the layer‐type and clump‐type plasma structures intercepted by a fan‐like effective radar beam are, respectively, in highly elongated and nearly circular shapes. The mean height of the clump‐type plasma structures is slightly higher than that of the layer‐type plasma structures by about 5 km. From interferometry‐measured echo distributions about the perpendicularity to the local magnetic field line, it is found that the mean aspect angle of the 3‐m field‐aligned irregularities for the layer‐type plasma structures is about 0.05° smaller than that for the clump‐type plasma structures. In addition, the height dependence of the aspect angle of the layer‐type plasma structures is different from that of the clump‐type plasma structures. The former tends to increase with height, while the later decreases with altitude. The zonal trace velocities of the layer‐type and clump‐type plasma structures estimated from their temporal displacements in the horizontal plane are, respectively, in ranges of −150–100 m/s and −180–80 m/s, in which negative (positive) values indicate eastward (westward) drift. The characteristics of the Doppler spectra of the echoes from the layer‐type and clump‐type plasma structures are also analyzed and the relations between the spectral parameters and the aspect angles are also discussed in this article.