Simultaneous occurrence of ionization ledge and counterelectrojet in the equatorial ionosphere: observational evidence and its implications

In this paper we present observational evidence for the simultaneous occurrence of an ionization ledge in the topside and a counterelectrojet in the E-region altitudes of the equatorial ionosphere. The following morphological features of the ionization ledge are found to be the same as those of the counterelectrojet phenomenon: namely, occurrence on a sequence of days in succession, preferential occurrence during a solar minimum period as compared with a solar maximum period, occurrence in a limited longitudinal belt, and lunar control of the occurrence as revealed by our data.There is also a high degree of correlation on both magnetically quiet and magnetically disturbed days between the ionization ledge and the counterelectrojet. Our study brings out a close coupling in the occurrence and morphological features of the two low-latitude phenomena, even though they are widely separated in altitude. The implications of such a correlation, with special reference to the understanding of the dynamical coupling of the E and F regions in the equatorial ionosphere, are briefly discussed.We also report a hitherto unreported feature of the ionization anomaly, viz., its occurrence on certain days in a narrow (~30°) longitude belt. The observational evidence presented in this paper may lead to new insights into the understanding of the interrelationships between the three phenomena, the ionization ledge, the ionization anomaly, and the counterelectrojet, in the equatorial ionosphere.

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A review of Cryphocricos Signoret, 1850 (Naucoridae: Cryphocricinae) with descriptions of three new species

Zootaxa ◽

10.11646/zootaxa.4958.1.7 ◽

2021 ◽

Vol 4958 (1) ◽

pp. 72-94

Author(s):

ROBERT W. SITES

Keyword(s):

New Species ◽

Molecular Phylogeny ◽

Intraspecific Variation ◽

New World ◽

Morphological Features ◽

Type Specimens ◽

Three New Species ◽

Aquatic Bugs ◽

High Degree

The genus Cryphocricos Signoret, 1850 was recently determined in a molecular phylogeny to be distantly related to other taxa of the subfamily Cryphocricinae to the extent that it is now once again the sole member of the subfamily. This exclusively New World group of aquatic bugs lives in fast and usually turbulent current and respires by means of a plastron. Efforts to identify morphological features to distinguish among the species have largely fallen short, and some species have been established based on features that exhibit a high degree of intraspecific variation overlapping those of other species. Presented here is a review of the 13 described species with discussions of their features and photos of type specimens, and three new species from Venezuela and Colombia are described. Also presented is a diagnostic attribute unique to the enigmatic Cryphocricos barozzii Signoret, 1850.

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Effects of solar eclipse on the electrodynamical processes of the equatorial ionosphere: a case study during 11 August 1999 dusk time total solar eclipse over India

Annales Geophysicae ◽

10.5194/angeo-20-1977-2002 ◽

2002 ◽

Vol 20 (12) ◽

pp. 1977-1985 ◽

Cited By ~ 26

Author(s):

R. Sridharan ◽

C. V. Devasia ◽

N. Jyoti ◽

Diwakar Tiwari ◽

K. S. Viswanathan ◽

...

Keyword(s):

Electric Fields ◽

Solar Eclipse ◽

Equatorial Ionosphere ◽

Hf Radar ◽

F Region ◽

Large Enhancement ◽

Temporal Structures ◽

E Region ◽

Field Lines ◽

Electric Fields And Currents

Abstract. The effects on the electrodynamics of the equatorial E- and F-regions of the ionosphere, due to the occurrence of the solar eclipse during sunset hours on 11 August 1999, were investigated in a unique observational campaign involving ground based ionosondes, VHF and HF radars from the equatorial location of Trivandrum (8.5° N; 77° E; dip lat. 0.5° N), India. The study revealed the nature of changes brought about by the eclipse in the evening time E- and F-regions in terms of (i) the sudden intensification of a weak blanketing ES-layer and the associated large enhancement of the VHF backscattered returns, (ii) significant increase in h' F immediately following the eclipse and (iii) distinctly different spatial and temporal structures in the spread-F irregularity drift velocities as observed by the HF radar. The significantly large enhancement of the backscattered returns from the E-region coincident with the onset of the eclipse is attributed to the generation of steep electron density gradients associated with the blanketing ES , possibly triggered by the eclipse phenomena. The increase in F-region base height immediately after the eclipse is explained as due to the reduction in the conductivity of the conjugate E-region in the path of totality connected to the F-region over the equator along the magnetic field lines, and this, with the peculiar local and regional conditions, seems to have reduced the E-region loading of the F-region dynamo, resulting in a larger post sunset F-region height (h' F) rise. These aspects of E-and F-region behaviour on the eclipse day are discussed in relation to those observed on the control day.Key words. Ionosphere (electric fields and currents; equatorial ionosphere; ionospheric irregularities)

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Lectotypification of names of three species of Poa (Poaceae) and their morphological affinities

Phytotaxa ◽

10.11646/phytotaxa.525.2.5 ◽

2021 ◽

Vol 525 (2) ◽

pp. 147-155

Author(s):

RUMA BHADRA ◽

P. V. PRASANNA ◽

SAIKAT NASKAR

Keyword(s):

Morphological Features ◽

Plant Parts ◽

Voucher Specimens ◽

High Degree

Poa aitchisonii, P. falconeri and P. wardiana are lectotypified with nomenclatural notes. In absence of proper icons with analysis, worked out plant parts of two species from voucher specimens are provided as photoplates. Due to high degree of variability and in absence of concrete morphological features to distinguish species, morphological affinities of the three species with that of other close species are provided.

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Simultaneous VHF radar backscatter and ionosonde observations of low-latitude E region

Annales Geophysicae ◽

10.5194/angeo-23-773-2005 ◽

2005 ◽

Vol 23 (3) ◽

pp. 773-779 ◽

Cited By ~ 8

Author(s):

A. K. Patra ◽

S. Sripathi ◽

P. B. Rao ◽

K. S. V. Subbarao

Keyword(s):

Low Latitude ◽

Vhf Radar ◽

Radar Echoes ◽

First Results ◽

E Region ◽

Gradient Drift ◽

Drift Instability ◽

Relationship Of ◽

The Relationship ◽

Field Aligned Irregularities

Abstract. The first results of simultaneous observations made on the low-latitude field-aligned irregularities (FAI) using the MST radar located at Gadanki (13.5° N, 79.2° E, dip 12.5°) and the Es parameters using an ionosonde at a nearby station Sriharikota (13.7° N, 80.1° E, dip 12.6°) are presented. The observations show that while the height of the most intense radar echoes is below the virtual height of Es (h'Es) during daytime, it is found to be either below or above during nighttime. The strength of the FAI is better correlated with the top penetration frequency (ftEs) and the blanketing frequency (fbEs) during the night (r=0.4 in both cases) as compared to the day (r=0.35 and -0.04, respectively). Furthermore, the signal strength of FAI is reasonably correlated with (ftEs-fbEs) during daytime (r=0.59) while very poorly correlated during nighttime (r=0.18). While the radar observations in general appear to have characteristics close to that of mid-latitudes, the relationship of these with the Es parameters are poorer than that of mid-latitudes. The observations reported here, nevertheless, are quite consistent with the expectations based on the gradient drift instability mechanism.

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Morphological study of the field-aligned E-layer irregularities observed by the Gadanki VHF radar

Annales Geophysicae ◽

10.5194/angeo-22-3799-2004 ◽

2004 ◽

Vol 22 (11) ◽

pp. 3799-3804 ◽

Cited By ~ 1

Author(s):

C. J. Pan ◽

P. B. Rao

Keyword(s):

Geomagnetic Latitude ◽

Spectral Width ◽

Statistical Characteristics ◽

Low Latitude ◽

Vhf Radar ◽

Lower Altitude ◽

Radar Echoes ◽

E Region ◽

Sporadic E ◽

Total Observation

Abstract. We report on the field-aligned irregularities observed in the low-latitude sporadic E-layer (Es) with the Gadanki (13.5° N, 79.2° E; geomagnetic latitude 6.3° N) VHF radar. The radar was operated intermittently for 15 days during the summer months in 1998 and 1999, for both daytime and nighttime observation. The total observation periods are 161h for the nighttime and 68h for the daytime. The observations were used to study the percentage of occurrence of the E-region echoes for both daytime and nighttime. The statistical characteristics of the mean radial velocity and spectral width are presented for three cases based on the echo occurrence characteristics and the altitude of observations (from 90 to 140km ranges), namely, the lower E-region daytime (90-110km), the lower E-region nighttime (90-105km) and the upper E-region nighttime (105-140km) echoes. The results are compared with that of Piura, a low-latitude station located at about the same geomagnetic latitude, but to the south of the equator. By comparing the behaviors of the lower E-region radar echoes of the summer months between Gadanki and Piura, we find that the lower altitude echoes below about 100km are rarely reported in Piura but commonly seen in Gadanki. Features of the nighttime echoes observed by these two radars are quite similar but daytime FAI echoes are again seldom detected by Piura.

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Some important factors that affect the Doppler properties of vertical m-size echoes in the low latitude E region

10.1190/sbgf2005-399 ◽

2005 ◽

Author(s):

J.-P. St.-Maurice* ◽

R. K. Choudhary

Keyword(s):

Low Latitude ◽

E Region

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A comparison of velocity measurements from the CUTLASS Finland radar and the EISCAT UHF system

Annales Geophysicae ◽

10.1007/s00585-999-0892-9 ◽

1999 ◽

Vol 17 (7) ◽

pp. 892-902 ◽

Cited By ~ 24

Author(s):

J. A. Davies ◽

M. Lester ◽

S. E. Milan ◽

T. K. Yeoman

Keyword(s):

Total Duration ◽

Field Of View ◽

Simultaneous Occurrence ◽

Plasma Convection ◽

Contributing Factors ◽

Plasma Irregularities ◽

Incoherent Scatter ◽

F Region ◽

Initial Comparison ◽

E Region

Abstract. The CUTLASS Finland radar, which comprises an integral part of the SuperDARN system of HF coherent radars, provides near continuous observations of high-latitude plasma irregularities within a field-of-view which extends over some four million square kilometres. Within the Finland radar field-of-view lie both the EISCAT mainland and EISCAT Svalbard incoherent scatter radar facilities. Since the CUTLASS Finland radar commenced operation, in February 1995, the mainland EISCAT UHF radar has been run in common programme 1 and 2 modes for a total duration exceeding 1000 h. Simultaneous and spatially coincident returns from these two radars over this period provide the basis for a comparison of irregularity drift velocity and F-region ion velocity. Initial comparison is limited to velocities from four intervals of simultaneous radar returns; intervals are selected such that they exhibit a variety of velocity signatures including that characteristic of the convection reversal and a rapidly fluctuating velocity feature. Subsequent comparison is on a statistical basis. The velocities measured by the two systems demonstrate reasonable correspondence over the velocity regime encountered during the simultaneous occurrence of coherent and incoherent scatter; differences between the EISCAT UHF measurements of F-region ion drift and the irregularity drift velocities from the Finland radar are explained in terms of a number of contributing factors including contamination of the latter by E-region echoes, a factor which is investigated further, and the potentially deleterious effect of discrepant volume and time sampling intervals.Key words. Ionosphere (ionospheric irregularities; plasma convection)

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