Observations of substorm associated absorption events on a 3200 km high latitude HF propagation path

1994 ◽  
Author(s):  
S.E. Milan
Keyword(s):  
High Latitude ◽  
Propagation Path ◽  
Hf Propagation

scholarly journals Geomechanical key parameters of the process of hydraulic fracturing propagation in fractured medium

2019 ◽  
Vol 74 ◽  
pp. 58 ◽  
Author(s):  
Rouhollah Basirat ◽  
Kamran Goshtasbi ◽  
Morteza Ahmadi
Keyword(s):  
Hydraulic Fracturing ◽  
Numerical Models ◽  
Fractured Reservoirs ◽  
Natural Fracture ◽  
Propagation Path ◽  
Fracture Density ◽  
Strength Parameters ◽  
Propagation Process ◽  
Fractured Medium ◽  
Hf Propagation

Hydraulic Fracturing (HF) is a well-stimulation technique that creates fractures in rock formations through the injection of hydraulically pressurized fluid. Because of the interaction between HF and Natural Fractures (NFs), this process in fractured reservoirs is different from conventional reservoirs. This paper focuses mainly on three effects including anisotropy in the reservoir, strength parameters of discontinuities, and fracture density on HF propagation process using a numerical simulation of Discrete Element Method (DEM). To achieve this aim, a comprehensive study was performed with considering different situations of in situ stress, the presence of a joint set, and different fracture network density in numerical models. The analysis results showed that these factors play a crucial role in HF propagation process. It also was indicated that HF propagation path is not always along the maximum principal stress direction. The results of the numerical models displayed that the affected area under HF treatment is decreased with increasing the strength parameters of natural fracture and decreasing fracture intensity.

scholarly journals Substorm correlated absorption on a 3200 km trans-auroral HF propagation path

1996 ◽  
Vol 14 (2) ◽  
pp. 182-190 ◽  
Author(s):  
S. E. Milan ◽  
T. B. Jones ◽  
M. Lester ◽  
E. M. Warrington ◽  
G. D. Reeves
Keyword(s):  
High Energy ◽  
Electron Precipitation ◽  
Propagation Path ◽  
Expansion Phase ◽  
Experimental Campaign ◽  
High Energy Electrons ◽  
Hf Propagation ◽  
Median Level ◽  
D Region ◽  
Asymmetric Behaviour

Abstract. A high-frequency transmitter located at Clyde River, NWT, Canada, and a receiver located near Boston, USA, provide a 3200 km trans-auroral, near-meridional propagation path over which the propagation characteristics have been measured. Out of the fourteen frequencies in the HF band sampled every hour for the duration of the experimental campaign (16 January–8 February 1989), the signal level measurements of 6.800 MHz transmissions were selected in order to determine the extent and occurrence of auroral absorption. The median level of auroral absorption along the path is found to increase with geomagnetic activity, quantified by the index Kp, with the increase being greater in the post-midnight sector than in the pre-midnight sector. This asymmetric behaviour is attributed to the precipitation of high energy electrons into the midnight and morning sector auroral D region. The measured diurnal variation in the median level of absorption is consistent with previous models describing the extent and magnitude of auroral absorption and electron precipitation. Individual substorms, identified from geosynchronous satellite data, are found to cause short-lived absorption events in the HF signal level of ~30 dB at 6.800 MHz. The occurrence of substorm correlated auroral absorption events is confined to the midnight and morning sectors, consistent with the location of the electron precipitation. The magnitude of absorption is related to the magnetotail stress during the substorm growth phase and the magnetotail relaxation during the substorm expansion phase onset. The absorption magnitude and the occurrence of substorms during the period of the campaign increase at times of high Kp , leading to an increase in median auroral absorption during disturbed periods.

Instantaneous maps of the European middle and high-latitude ionosphere for HF propagation assessments

1998 ◽  
Vol 22 (6) ◽  
pp. 861-864 ◽  
Author(s):  
P.A. Bradley ◽  
G. Juchnikowski ◽  
H. Rothkaehl ◽  
I. Stanislawska
Keyword(s):  
High Latitude ◽  
Hf Propagation ◽  
High Latitude Ionosphere
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