Toward Scatter Classification at Middle Latitudes

Transcription

1 Toward Scatter Classification at Middle Latitudes E. S. Miller and E. R. Talaat Geospace and Earth Science Group Johns Hopkins University Applied Physics Laboratory 31 May 2011

2 SuperDARN Network

3 SuperDARN Network

4 SuperDARN Network

5 Mid-Latitude SuperDARN Installed to observe expansion of convection pattern equatorward of traditional SuperDARN boundaries. This happens with some regularity, but quiet conditions prevail. What is observed during quiet time? Signal to one is noise to another. scatter {ionospheric, ground} does not describe mid-latitude variability accurately. scatter {ionospheric, ground} algorithm does not describe mid-latitude physics accurately. Consider first climatological behavior.

6 Wallops Island Climatology 2009 Wallops Island SuperDARN beam #7 backscatter power > 10 db Climatology Virtual Range [km] khz khz Universal Time [hrs] Occurrence [pct]

7 Wallops Island Climatology Virtual Range [km] Wallops Island SuperDARN beam #7 backscatter power > 10 db Climatology khz khz Universal Time [hrs] Sub-Auroral Trough Irregularities in the sub-auroral trough produce significant backscatter on many nights. (See Talaat, et al, poster.) Meteor Echoes Ablating meteors deposit trails of metallic ions in the E region. Sporadic-E layers also contribute to this prevalence Occurrence [pct] Ground Scatter Echoes returned off of the land or sea.

8 Propagation Mechanisms Refraction

9 Propagation Mechanisms Refraction B k Field-Aligned Irregularities (FAI)

10 Propagation Mechanisms Refraction B k Field-Aligned Irregularities (FAI) Specular Reflection k Density Structure

11 Meteor Scatter Essentially all SuperDARN meteor scatter is specular. FAI typically observed by powerful IS-class radars. Meteor trails have short lifetimes ( 100 ms). Individual trails usually only appear in one range gate in space and time. Ensemble of many trails yields cloud of scatter at close ranges.

12 Sporadic-E Thin, dense, turbulent layer of metallic ions at E-region altitudes. Specular echoes, FAI, ground scatter, all possibilities. Separating specular echoes from FAI? Sporadic-E over Arecibo. After Swartz, et al, 2002.

13 Raytracing Need not be complicated to be informative. Parabolic or Chapman profiles driven by standard URSI coefficients. Or interpolate other datasets, use IRI (called directly from MATLAB). Geomagnetic field (IGRF is easy in MATLAB). Basic Appleton-Hartree magneto-ionic effects. Loosely based on Jones-Stephenson code, but only for 2.5D. Find ground scatter location. Find k B possible FAI location.

14 Wallops Predictions Wallops Island SuperDARN beam # khz O-mode 500 Wallops Island Millstone Hill Altitude [km] k B East Geographic Longitude [deg] North Geographic Latitude [deg] 65 Drive with Millstone Hill Digisonde. Wallops beam #7 passes directly over Millstone.

15 Wallops Predictions Virtual Range [km] σ 3000 GS 2000 FAI mean σ Universal Time [hr]

16 Scatter Geolocation Tool Altitude [km] Wallops Island 70 Wallops Island SuperDARN beam # khz O-mode 65 Millstone Hill East Geographic Longitude [deg] 60 k 55 B North Geographic Latitude [deg] Convert pretty (but useless) 3D plot to Virtual Range vs altitude. 65 Virtual Range [km] Virtual Range [km] SuperDARN Wallops Island beam #7 fof2 = 4 MHz, frad = 10.5 MHz 2500 O-mode GS-F FAI-E FAI-F Altitude [km] fof2 = 5 MHz, frad = 10.5 MHz 2500 O-mode GS-F FAI-E FAI-F Altitude [km]

17 Scatter Geolocation Tool Triple-hop sporadic-e (G-E s ) ground scatter UT. Field-aligned irregularity (FAI) scatter from locations where k B. Differentiate between FAI-F and G-E s using Doppler velocity. Virtual Range [km] F ground scatter Es ground scatter F FAI scatter May Wallops Island SuperDARN beam # MHz G-Es FAI-F 200 E FAI scatter 200 FAI-Es Universal Time [hrs] Altitude [km]

18 Discussion Mid-latitudes exhibit new and subtle sources of SuperDARN scatter. Non-auroral FAI. Sporadic-E. Raytracing and phenomenology provide some guidance. Not operational, but good for case studies. Interferometer elevation can also help (not active at Wallops presently). Raytracing in inhomogeneous ionosphere for irregularity studies.