scholarly journals A comparative study of night-time enhancement of TEC at a low latitude station on storm and quiet nights including the local time, seasonal and solar activity dependence

2002 ◽  
Vol 20 (11) ◽  
pp. 1843-1850 ◽  
Author(s):  
K. Unnikrishnan ◽  
R. Balachandran Nair ◽  
C. Venugopal
Keyword(s):  
Solar Activity ◽  
Mean Amplitude ◽  
Occurrence Frequency ◽  
Plasma Convection ◽  
Night Time ◽  
Low Latitude ◽  
Latitude Station ◽  
Different Seasons ◽  
The Mean ◽  
Activity Dependence

Abstract. The main characteristics of night-time enhancements in TEC during magnetic storms are compared with those during quiet nights for different seasons and solar activity conditions at Palehua, a low latitude station during the period 1980–1989. We find that the mean amplitude has both a seasonal and solar activity dependence: in winter, the values are higher for weak storms as compared to those during quiet nights and increase with an increase in solar activity. In summer, the mean amplitude values during weak storms and quiet nights are almost equal. But during equinox, the mean amplitude values for quiet nights are greater than those during weak storms. The mean half-amplitude duration is higher during weak storms as compared to that during quiet nights in summer. However, during winter and equinox, the durations are almost equal for both quiet and weak storm nights. For the mean half-amplitude duration, the quiet night values for all the seasons and equinoctial weak storm values increase with an increase in solar activity. The occurrence frequency (in percent) of TEC enhancement during weak storms is greater than during quiet nights for all seasons. The mean amplitude, the mean half-amplitude duration and the occurrence frequency (in percent) of TEC enhancement values are higher during major storms as compared to those during quiet nights. The above parameters have their highest values during pre-midnight hours. From the data analysed, this behaviour is true in the case of major storms also.Key words. Ionosphere (ionospheric disturbances; plasma convection) Magnetospheric physics (storms and substorms)

scholarly journals Characteristics of VHF radiowave scintillations over a solar cycle (1983−1993) at a low-latitude station: Waltair (17.7°N, 83.3°E)

1997 ◽  
Vol 15 (6) ◽  
pp. 729-733 ◽  
Author(s):  
P. V. S. Rama Rao ◽  
P. T. Jayachandran ◽  
P. Sri Ram ◽  
B. V. Ramana Rao ◽  
D. S. V. V. D. Prasad ◽  
...  
Keyword(s):  
Solar Activity ◽  
Solar Cycle ◽  
High Solar Activity ◽  
Night Time ◽  
Low Latitude ◽  
Latitude Station ◽  
Maximum Occurrence

Abstract. The characteristics of VHF radiowave scintillations at 244 MHz (FLEETSAT) during a complete solar cycle (1983–93) at a low-latitude station, Waltair (17.7°N, 83.3°E), are presented. The occurrence of night-time scintillations shows equinoctial maxima and summer minima in all the epochs of solar activity, and follows the solar activity. The daytime scintillation occurrence is negatively correlated with the solar activity and shows maximum occurrence during the summer months in a period of low solar activity. The occurrence of night-time scintillations is inhibited during disturbed days of high solar activity and enhanced during low solar activity.

Vertical TEC variations and model during low solar activity at a low latitude station, Xiamen

2012 ◽  
Vol 49 (3) ◽  
pp. 530-538 ◽  
Author(s):  
Guoqi Liu ◽  
Wengeng Huang ◽  
Hua Shen ◽  
Jiancun Gong
Keyword(s):  
Solar Activity ◽  
Low Latitude ◽  
Latitude Station

scholarly journals HF Doppler radar observations of sporadic E at an Indian low latitude station, Visakhapatnam

2009 ◽  
Vol 27 (2) ◽  
pp. 537-545 ◽  
Author(s):  
M. S. S. R. K. N Sarma ◽  
C. Raghava Reddy ◽  
K. Niranjan
Keyword(s):  
Doppler Radar ◽  
Doppler Velocity ◽  
Night Time ◽  
Low Latitude ◽  
Radar Observations ◽  
Latitude Station ◽  
Velocity Variations ◽  
Sporadic E ◽  
Gradient Drift ◽  
Drift Instability

Abstract. 5.5 MHz HF Doppler radar observations of Sporadic E over an Indian low latitude station, Visakhapatnam (17.7° N, 83.3° E and Dip 20°) with 10 s resolution showed quasi-periodic variations of the echo strength and Doppler velocity variations with periods of a few minutes to a few tens of minutes. The echo strength and Doppler velocity variations with time in different range bins of the ES echo showed variations which are some times similar and some times significantly different in successive range bins at intervals of 7.5 km. The ES echo occurs with the height of maximum echo strength in the range of 100 km to 120 km and some times at 130 km. The altitude variation of the average Doppler velocity is highly variable and the height of maximum echo strength is not the same as the height of maximum Doppler velocity. Observations of ES echoes at different times of the day are presented to bring out the differences between the day and night time ES echoes. The relationship between Radar and ES parameters derived from Ionograms is poorer than that of mid latitudes which is quite consistent with the expectations based on gradient drift instability.

scholarly journals Can irregularities of solar proxies help understand quasi-biennial solar variations?

2014 ◽  
Vol 21 (4) ◽  
pp. 797-813 ◽  
Author(s):  
A. Shapoval ◽  
J. L. Le Mouël ◽  
M. Shnirman ◽  
V. Courtillot
Keyword(s):  
Solar Activity ◽  
Solar Cycle ◽  
Mean Amplitude ◽  
Embedding Dimension ◽  
Sliding Windows ◽  
Irregularity Index ◽  
Daily Series ◽  
Poissonian Noise ◽  
The Mean ◽  
R Value

Abstract. We define, calculate and analyze irregularity indices λISSN of daily series of the International Sunspot Number ISSN as a function of increasing smoothing from N = 162 to 648 days. The irregularity indices λ are computed within 4-year sliding windows, with embedding dimensions m = 1 and 2. λISSN displays Schwabe cycles with ~5.5-year variations ("half Schwabe variations" HSV). The mean of λISSN undergoes a downward step and the amplitude of its variations strongly decreases around 1930. We observe changes in the ratio R of the mean amplitude of λ peaks at solar cycle minima with respect to peaks at solar maxima as a function of date, embedding dimension and, importantly, smoothing parameter N. We identify two distinct regimes, called Q1 and Q2, defined mainly by the evolution of R as a function of N: Q1, with increasing HSV behavior and R value as N is increased, occurs before 1915–1930; and Q2, with decreasing HSV behavior and R value as N is increased, occurs after ~1975. We attempt to account for these observations with an autoregressive (order 1) model with Poissonian noise and a mean modulated by two sine waves of periods T1 and T2 (T1 = 11 years, and intermediate T2 is tuned to mimic quasi-biennial oscillations QBO). The model can generate both Q1 and Q2 regimes. When m = 1, HSV appears in the absence of T2 variations. When m = 2, Q1 occurs when T2 variations are present, whereas Q2 occurs when T2 variations are suppressed. We propose that the HSV behavior of the irregularity index of ISSN may be linked to the presence of strong QBO before 1915–1930, a transition and their disappearance around 1975, corresponding to a change in regime of solar activity.

scholarly journals A new method for retrieval of the extinction coefficient of water clouds by using the tail of the CALIOP signal

2010 ◽  
Vol 10 (11) ◽  
pp. 28151-28181 ◽  
Author(s):  
J. Li ◽  
Y. Hu ◽  
J. Huang ◽  
K. Stamnes ◽  
Y. Yi
Keyword(s):  
Extinction Coefficient ◽  
New Method ◽  
Lidar Signal ◽  
Night Time ◽  
Extinction Coefficients ◽  
Low Level ◽  
Different Seasons ◽  
Water Cloud ◽  
The Mean ◽  
Global Mean

Abstract. A method is developed based on Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) level 1 attenuated backscatter profile data for deriving the mean extinction coefficient of water droplets close to cloud top. The method is applicable to low level (cloud top < 2 km), opaque water clouds in which the lidar signal is completely attenuated beyond about 100 m of penetration into the cloud. The photo multiplier tubes (PMTs) of 532 nm detectors (parallel and perpendicular polarizations) of Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) both exhibit a non-ideal recovery of the lidar signal after striking a strongly backscattering target (such as water cloud or surface). Therefore, the effects of any transient responses of CALIOP on the attenuated backscatter profile of the water cloud must first be removed in order to obtain a reliable (validated) attenuated backscatter profile. Then, the slope of the exponential decay of the validated water cloud attenuated backscatter profile, and the multiple scattering factor are used for deriving the mean extinction coefficient of low-level water cloud droplets close to cloud top. This novel method was evaluated and compared with the previous method by combining the cloud effective radius (3.7 μm) reported by MODIS with the lidar depolarization ratios measured by CALIPSO to estimate the mean extinction coefficient. Statistical results show that the extinction coefficients derived by the new method based on CALIOP alone agree reasonably well with those obtained in the previous study using combined CALIOP and MODIS data. Their mean absolute relative difference in extinction coefficient is about 13.4%. An important advantage of the new method is that it can be used to derive the extinction coefficient also during night time, and it is also applicable when multi-layered clouds are present. Overall, the global mean cloud water extinction coefficients during different seasons range from 26.17 to 29.46 km−1, and the differences between day and night time all are small (about 1 km−1). However, the global mean layer-integrated depolarization ratios of water cloud during different seasons range from 0.2 to 0.23, and the differences between day and night also are small, about 0.01.

scholarly journals The occurrence altitudes of middle atmospheric temperature inversions and mesopause over low-latitude Indian sector

2014 ◽  
Vol 32 (8) ◽  
pp. 967-974 ◽  
Author(s):  
M. Sivakandan ◽  
D. Kapasi ◽  
A. Taori
Keyword(s):  
Solar Activity ◽  
Atmospheric Temperature ◽  
Occurrence Rate ◽  
High Solar Activity ◽  
Night Time ◽  
Low Latitude ◽  
Small Peak ◽  
Occurrence Characteristics ◽  
Temperature Inversions ◽  
Indian Sector

Abstract. We study the occurrence characteristics of mesospheric inversion layers (MILs) in the 60–105 km altitude region over the low-latitude Indian sector. We note that lower inversions in the mesospheric temperatures occur in the 70–75 km altitude regions while the upper inversions occur in 90–95 km altitude regions. The mesopause altitude is mostly noted to be ~ 98 km with the night-time mesopause (particularly in the year 2002) showing a small peak in the mesopause occurrence at ~ 75 km altitude. We note higher occurrence rate of MILs during high solar activity year compared to low solar activity year. It is also observed that night time MILs show a systematic seasonal variability, with higher occurrence of single and double temperature inversions during equinoxes.

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