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.

(2010), Reply to comment by Lei et al. on "A new aspect of ionospheric E region electron density morphology," J. Geophys. Res., 115, A07314, doi:10.1029 [1] Since the FORMOSAT-3/COSMIC satellites were launched in April 2006, ionospheric electron density profiles have been retrieved from the excess phase of the GPS signal by using the radio occultation technique and can be accessed from the Web site http://www.cosmic.ucar.edu/. On the basis of these electron density profiles and the use of data quality control criteria developed by Yang et al. [2009], Chu et al.[2009] investigated E region electron density morphology and showed that the general properties of the COSMICretrieved E region electron density are in good agreement with the predictions of the Chapman layer theory that was developed in accordance with photochemical process and controlled by solar zenith angle. Nevertheless, Chu et al.[2009] found existences of salient enhancements in the noontime E region electron density not only at the geomagnetic equator but also in the geomagnetic latitude regions ±15°−35°, which cannot be explained by the Chapman layer theory. In addition, they also provided compelling evidence to show the presence of longitudinal wave number 3 and 4 structures of the equatorial electron density in a height range of 100-200 km, which is in excellent agreement with longitudinal structures of equatorial electrojet intensity derived from equatorial magnetic field data obtained by the Ørsted, CHAMP, and SAC-C satellites during the years 1999-2006.[2] On the basis of the simulation result obtained by Yue et al. [2010], Lei et al. [2010] question the validity of the E region electron density retrieved by the GPS radio occultation technique. They argue that because of the presence of the ionospheric electron density gradient in the horizontal direction that violates the spherical symmetry assumption of the Abel transform for inverting ionospheric electron density profile from calibrated total electron content along the GPS raypath, the COSMIC-measured E region electron density enhancements in midlatitude regions were caused by the retrieval error of the GPS radio occultation process. From Figure 1 of Lei et al. [2010] were true and able to be representative of the general GPS occultation-retrieved results, the morphologies of the COSMIC-measured E region electron density should be in accord with those of the simulation results. Namely, the E region electron density retrieved by COSMIC satellites should be much greater (smaller) than true measurement made by the ground-based ionosonde in geomagnetic latitude regions ±30°-50°(±10°-30°). In order to validate the simulation-retrieved results, we compare peak values of E layer electron density N m E between COSMIC retrieval and global ionosonde measurement in the different latitudinal regions for July 2006 to July 2009. The COSMIC data were selected for comparison if the separation between COSMIC occultation point and ionosonde station is 10 min in time and 2.5°in space. As shown in Figure 1, ...

In this ar ti cle, we an a lyze the prop er ties of ion o spheric elec tron den sity pro fil ing re trieved from FORMOSAT-3/COS MIC ra dio occultation mea sure ments. Two pa ram e ters, namely, the gra di ent and fluc tu a tion of the top side elec tron den sity pro file, serve as in di ca tors to quan ti ta tively de scribe the data qual ity of the re trieved elec tron den sity pro file. On the ba sis of 8 month data (June 2006 -Jan u ary 2007), we find that on av er age 93% of the elec tron den sity pro files have up per elec tron den sity gra di ents and elec tron den sity fluc tu a tions smaller than -0.02 #/m 3 /m and 0.2, re spec tively, which can be treated as good data for fur ther anal y sis. The same re sults are also achieved for the peak height of the elec tron den sity. Af ter re mov ing the ques tion able data, we com pare the gen eral be hav iors of the elec tron den sity be tween FORMOSAT-3 and the IRI model. It is found that the global dis tri bu tions of the peak height and the peak elec tron den sity for the FORMOSAT-3/COS MIC data are gen er ally con sis tent with those for the IRI model. How ever, a sig nif i cant dif fer ence be tween their scale heights of the top side elec tron den sity pro files is found. It sug gests that the shape of the top side elec tron den sity pro file in the IRI model should be revised accordingly such that it more closely resembles the real situation. Ocean. Sci., 20, 193-206, doi: 10.3319/TAO.2007.10.05.01(F3C) IN TRO DUC TIONRa dio occultation tech nique is an old, but very so phis ticated, method for the re trieval ter res trial at mo sphere parameters (Fjeldbo et al. 1971). The core of this tech nique is (under a num ber of as sump tions) to trans form the bend ing an gle of the ra dio ray path to the at mo spheric re frac tive index, which is trans mit ted from a very sta ble source sit u ated on one side of the Earth and re ceived by a re ceiver lo cated on the op po site side of the Earth (Rocken et al. 1997;Hajj et al. 2000). Once the at mo spheric re frac tive in dex is re trieved, the lower at mo spheric tem per a ture, hu mid ity and ion ospheric elec tron den sity at the tan gent point of the ray path pierc ing through the at mo sphere can be es ti mated in ac cordance with the re la tion be tween the re frac tive in dex n and the pa ram e ters given be low:( 1) where P is pres sure (hpa), T is tem per a ture (k), e is wa ter va por pres sure (hpa), f is ra dio wave fre quency (Hz), and n e is elec tron den sity (#/m 3 ). In the ion o sphere (higher than an al ti tude of about 100 km), the con tri bu tion of T, P and e to the at mo spheric re frac tive in dex is neg li gi ble com pared to the elec tron den sity con tri bu tion. As a re sult, n e can be directly es ti mated from n for given f. Ex cept for the at mospheric re frac tive in dex, un der the straight line as sump tion of the ra dio ray path, the height vari a tion of the ion o spheric elec tron den sity can also be re trieved from cal i brated to tal elec tron con tent (TEC) in ac cor...

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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 (⌳) and shape () 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 -⌳ 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 -⌳ relation is derived based on theoretical relations between gamma DSD moments and ⌳ and . It is shown that the derived -⌳ relation is independent of the order of the moment of the gamma DSD.The key factor dominating the -⌳ relation is the ratio of the number density parameter N(D m ) to total number density of the raindrop M 0 , where D m 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(D m )/M 0 that governs the slope of the -⌳ relation. A comparison between the derived and the empirical -⌳ relations shows that their behaviors are very similar, especially for large rainfall rates characterized by smaller ⌳ and values. Moreover, the ratio N(D m )/M 0 bears a weak relation to the rainfall rate R. Nevertheless, the square of the ratio M 0 /N(D m ) is closely related to the ratio R/M 0 and their relation can also be described by a seconddegree polynomial. Considering this property, the authors examine the validity of the various -⌳ relations by simulating the relations between R/M 0 and [M 0 /N(D m )] 2 . A comparison between observed and simulated results shows that the relation generated from the derived -⌳ relation bears the best resemblance to the observed one in both magnitude and shape.