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In this paper; dete~lination of the welding process parameters for obtaining an optimal weld bead geomet~ in gas tungsten arc welding is presented. The Taguchi method is used to formulate the experimental layout, to analyse the effect of each welding process parameter on the weld bead geometry, and to predict the optimal setting for each welding process parameter. Experimental results are presented to explain the proposed approach.

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Abstract. Empirical models of Total Electron Content (TEC) based on functional fitting over Taiwan (120 • E, 24 • N) have been constructed using data of the Global Positioning System (GPS) from 1998 to 2007 during geomagnetically quiet condition (D st >−30 nT). The models provide TEC as functions of local time (LT), day of year (DOY) and the solar activity (F), which are represented by 1-162 days mean of F10.7 and EUV. Other models based on median values have been also constructed and compared with the models based on the functional fitting. Under same values of F parameter, the models based on the functional fitting show better accuracy than those based on the median values in all cases. The functional fitting model using daily EUV is the most accurate with 9.2 TECu of root mean square error (RMS) than the 15-days running median with 10.4 TECu RMS and the model of International Reference Ionosphere 2007 (IRI2007) with 14.7 TECu RMS. IRI2007 overestimates TEC when the solar activity is low, and underestimates TEC when the solar activity is high. Though average of 81 days centered running mean of F10.7 and daily F10.7 is often used as indicator of EUV, our result suggests that average of F10.7 mean from 1 to 54 day prior and current day is better than the average of 81 days centered running mean for reproduction of TEC. This paper is for the first time comparing the median based model with the functional fitting model. Results indicate the functional fitting model yielding a better performance than the median based one. Meanwhile we find that the EUV radiation is essential to derive an optimal TEC.

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Positive and negative signatures of the ionospheric storms caused by the penetration electric field, disturbance dynamo, neutral wind, neutral composition, etc., have been reported. In this paper, the ionospheric total electron content (TEC) derived from the records of a network of ground‐based GPS receivers in Taiwan is used to statistically study the characteristics such as local time of appearance and duration of the storm signatures of various casuals in the equatorial ionization anomaly (EIA) region during 1994–2003. A bias‐corrected accelerated bootstrap method and a z test are employed for the first time to detect each event, and the overall storm signatures and characteristics, respectively. It is found that the positive signatures that appeared minutes to hours after the geomagnetic storm onset are pronounced on the storm day and the next day, while the negative signatures that started hours after the geomagnetic storm onset can last for as long as the next 4 days. The positive signature is statistically significant and most pronounced, when the intense geomagnetic storm onset occurs during local afternoon, which suggests that the signature may result from a combination of the prompt penetration electric field effect and mechanical effects of equatorward neutral wind. Additionally, the negative signature that is statistically significant and most pronounced in the local afternoon of the storm‐onset day and/or the next day may be produced by the disturbance dynamo or overshielding effects. The long‐lasting negative signature occurred in local midnight‐noon period on days 2–4 after the storm onset may result from the neutral composition disturbances.