Accurately measuring the location and motion of the polar cap boundary (PCB) in the high-latitude ionosphere can be crucial for studies concerned with the dynamics of the polar cap, e.g. the measurement of reconnection rates. The Doppler spectral width characteristics of backscatter received by the SuperDARN HF radars have been previously used for locating and tracking the PCB in the cusp region. The boundary is generally observed in meridional beams of the SuperDARN radars and appears as a distinct change between low spectral width values observed equatorward of the cusp region, and high, but variable spectral width values observed within the cusp region. To identify the spectral width boundary (SWB) between these two regions, a simple algorithm employing a spectral width threshold has often been applied to the data. However, there is not, as yet, a standard algorithm, or spectral width threshold, which is universally applied. Nor has there been any rigorous assessment of the accuracy of this method of boundary determination. This study applies a series of threshold algorithms to a simulated cusp-region spectral width data set, to assess the accuracy of different algorithms. This shows that simple threshold algorithms correctly identify the boundary location in, at the most, 50% of the cases and that the average boundary error is at least similar to1-2 range gates (similar to1degrees latitude). It transpires that spatial and temporal smoothing of the spectral width data (e.g. by median filtering), before application of a threshold algorithm can increase the boundary determination accuracy to over 95% and the average boundary error to much less than a range gate. However, this is sometimes at the cost of temporal resolution in the motion of the boundary location. The algorithms are also applied to a year’s worth of spectral width data from the cusp ionosphere, measured by the Halley SuperDARN radar in Antarctica. This analysis highlights the increased accuracy of the enhanced boundary determination algorithm in the cusp region. Away from the cusp, the resulting SWB locations are often dependent on the choice of threshold. This suggests that there is not a sharp latitudinal SWB in regions of the dayside ionosphere away from the cusp, but that there is a shallower latitudinal gradient in spectral width near the boundary location.
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Mahendra Singh Dhoni is maintaining a “good habit” Virat Kohli had demanded after the first match of the one day international series in Sri Lanka. Dhoni once again produced a solid performance with the bat and ensured India win the third ODI to capture the five-match series 3-0.Dhoni joined Rohit Sharma in the middle after India were reduced to 61/4 in 15.1 overs in their chase of 218. However, Dhoni looked to be the man on a mission as he slowly but steadily kept the scoreboard ticking along with opener Rohit, who went on to score his 12th ODI hundred.Dhoni played a calm knock, scored in singles and twos and allowed Rohit to take the attack back to the Sri Lankan bowlers.This helped India nullify the threat of Akila Dananjaya who once again rocked India with a couple of wickets with his off-break bowling. Dananjaya had picked up his career-best 6/54 in the second ODI and once again looked to put India in trouble. But Dhoni, who stood between Dananjaya and Sri Lanka’s victory in the second game, was once again the man India pinned their hopes on.Special night with the special man. Great way to win the series. #WeMarchOn #IceMan&Hitman pic.twitter.com/qad1WfGaR8- Rohit Sharma (@ImRo45) August 28, 2017In the second ODI, India were staring at defeat at 131/7 chasing 231 when Dhoni and unlikely hero Bhuvneshwar Kumar stitched together an unbroken century partnership to give India a three-wicket win for 2-0 series lead.India were once again put in a kind of similar situation, tottering at 61/4 with Shikhar Dhawan (5), Virat Kohli (3), KL Rahul (17) and Kedar Jadhav (0) all back in the hut cheaply.advertisementBut Dhoni and Rohit forged a 157-run unbeaten partnership for the fifth wicket to guide India to their fifth successive ODI series triumph. The victory also helped India clinch their seventh consecutive ODI series against Sri Lanka.The former skipper was calm and cool as usual at the other end even as Rohit struck his maiden century in Sri Lanka, studded with 16 fours and a couple of big hits.Keep Calm and Carry On – @ImRo45 & @msdhoni #TeamIndia #SLvIND pic.twitter.com/tVSfYOl4RP- BCCI (@BCCI) August 27, 2017While Dhoni’s previous knock of 45 not out in the second game involved only one four, he belted a six and four fours in his unbeaten 68 off 86 deliveries in his 299th match.The 36-year-old also surpassed Mohammad Azharuddin’s tally of 9378 to become India’s fourth-highest run-getter in the 50-overs format behind Sachin Tendulkat, Sourav Ganguly and Rahul Dravid. Dhoni now has 9434 runs from 296 ODIs for India. He has also played three ODIs for Asia XI to take his aggregate score to 9608 runs.Dhoni loves batting against Sri Lanka and the stats don’t lie. In 61 ODIs, the wicketkeeper-batsman has scored 2261 runs at 64.60 with the help of two centuries and 18 fifties. His career-best of 183 not out also came against the island nation.Yet another match winning knock by Rohit and Mahi Bhai. Very well played. #IndianCricket #Cricket @ImRo45 @msdhoni #INDvSLPic: HT pic.twitter.com/qn1UjVW6kV- Ishant Sharma (@ImIshant) August 27, 2017Dhoni’s form and future has been under the scanner since his Test retirement in December 2014. He stepped down from limited-overs captaincy in January and handed over the reins to Virat Kohli in all the three formats.Since relinquishing captaincy, Dhoni has batted in 16 innings to score 498 runs at an average of 83 with the help of a century and four fifties.Yet another match winning knock by Rohit and Mahi Bhai. Very well played. #IndianCricket #Cricket @ImRo45 @msdhoni #INDvSLPic: HT pic.twitter.com/qn1UjVW6kV- Ishant Sharma (@ImIshant) August 27, 2017Enjoyed the way @ImRo45 batted tonight???Loved his positivity & maturity???One more crucial knock from @msdhoni ??? @BCCI- VVS Laxman (@VVSLaxman281) August 27, 2017