Abstract. By using the interferometry technique implemented at the Chung-Li VHF radar, the striated echoes with quasi-periodic characteristics in the range-time-intensity plot generated from the electron density irregularities associated with sporadic E layer are investigated. It is shown that the Es irregularities above 110 km drifting mostly westward along a stationary path of a few kilometer's width are responsible for the striated echoes. Considering the field-aligned property of the Es irregularities and the geometry of the echoing region over the Chung-Li radar site, it indicates that this stationary path is the cross section of a tilted layer which has a sharp electron density gradient in the direction across the layer parallel to the magnetic field line in the E region and orients geographically 72øNW. The observations also demonstrate that the echoing regions of the Es irregularities over the Chung-Li radar station are confined on the right side of a tilted thin plane with the thickness of a few kilometers at the elevation angle of 52 ø in the radar viewing region. These characteristics can be explained by using the radar backscatter from field-aligned targets in the field-perpendicular direction. The behavior of the sporadic E layer in the equatorial anomalous region is also investigated and discussed, and a descending sporadic E layer modulated by the gravity waves is observed. The descent rate of the layer is about 3.6 m/s, considerably larger than that reported by other investigators. The primary gravity wave modulating the sporadic E layer has a period of 12-15 min and propagates upward in phase with a vertical wavelength of about 50 km. Moreover, a positive correlation between the peak intensity of radar returns from Es irregularities below 110 km and the vertical shear of their horizontal drift velocity is seen. This feature, combined with the positive correlation between radar backscatter and the Doppler spectral width, strongly suggests that the crucial role the neutral wind plays in the excitation of the Es irregularities below 110 km cannot be ignored.

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...

No abstract

[1] Although the plausible mechanisms involved in the generation of midlatitude type 1 sporadic E (Es) irregularities have been suggested, rare observational evidence is provided to validate the proposed plasma structure associated with the midlatitude type 1 Es irregularities. In this article, the type 1 echoes observed by the Chung-Li VHF radar located in the equatorial anomalous region are interferometrically analyzed and the corresponding plasma structure of the type 1 irregularities is reconstructed. We find that the plasma structure has sharp lateral and top and bottom boundaries with thickness of about 1-2 km and horizontal extent of about 3-5 km in E-W direction. Its dimension in N-S direction cannot be resolved by using interferometry technique because of considerably narrow width of expected echoing region in elevation. The observed Doppler velocity of the type 1 echoes can be as low as 220 m/s, substantially smaller than nominal ion acoustic wave speed (about 360 m/s) in Es region. The spatial structure of the concurrent type 2 irregularities is also reconstructed. The result strongly suggests that it be a well-defined thin layer with thickness of 1-2 km and horizontal extent of 9-17 km in E-W direction, very different from that of the type 1 irregularities. The whole structure of type 1 irregularities moves bodily toward east at speed of about 31 m/s, and no vertical displacement of the structure is observed. Although the movement of the layer structure of the type 2 irregularities in E-W direction is indistinct, it descends remarkably at a rate of 10.3 m/s. These features imply that for the present case the factors governing the dynamic behavior of the type 1 and type 2 irregularities are different and independent, irrespective of the fact that the clump of the type 1 irregularities separates from that of concurrent type 2 irregularities only by about 4 km in distance.

No abstract