The occurrence of post-sunset equatorial spread-F (ESF) could have detrimental effects on trans-ionospheric radio wave propagation used in modern communications systems. This problem calls for a simple but robust model that accurately predicts the occurrence of post-sunset ESF. Logistic regression was implemented to model the daily occurrence of post-sunset ESF as a function of the evening upward plasma drift (v). The use of logistic regression is formalized by $\widehat{y}=1/\left[1+\exp \left(-z\right)\right]$, where $\widehat{y}$ represents the probability of post-sunset ESF occurrence, and $z$ is a linear function containing $v$. The value of $v$ is derived from the vertical motion of the bottom side of the F-region in the evening equatorial ionosphere, which is observed by the ionosondes in Southeast Asia. Data points (938) of v and post-sunset ESF occurrence were collected in the equinox seasons from 2003 to 2016. The training set used 70% of the dataset to derive $z$ and $\widehat{y}$ and the remaining 30% was used to test the performance of $\widehat{y}$. The expression $z=-2.25+0.14v$ was obtained from the training set, and $\widehat{y}\ge 0.5$ (v ≥ ~16.1 m/s) and $\widehat{y}<0.5$ (v < ~16.1 m/s) represented the occurrence and non-occurrence of ESF, respectively, with an accuracy of ~0.8 and a true skill score (TSS) of ~0.6. Similarly, in the testing set, $\widehat{y}$ shows an accuracy of ~0.8 and a TSS of ~0.6. Further analysis suggested that the performance of the z-function can be reliable in the daily F_10.7 levels ranging from 60 to 140 solar flux units. The z-function implemented in the logistic regression ($\widehat{y}$) found in this study is a novel technique to predict the post-sunset ESF occurrence. The performance consistency between the training set and the testing set concludes that the z-function and the $\widehat{y}$ values of the proposed model could be a simple and robust mathematical model for daily nowcasting the occurrence or non-occurrence of post-sunset ESFs.

Sejak tahun 1980 diyakini bahwa atmosfer penting tidak saja pada lapisan troposfer (proses cuaca) dan lapisan ionosfer (komunikasi radio), tetapi juga lapisan diantaranya. Hal itu didukung dengan pengembangan peralatan remote sensing seperti radar yang membantu menjelaskan proses-proses dinamis yang terjadi pada lapisan atmosfer dan ionosfer. Berbagai gelombang yang terjadi akibat proses-proses cuaca di lapisan troposfer berperan dalam menjalarkan momentum dan energi global dari troposfer ke lapisan atmosfer lebih atas. Gelombang gravitasi dan pasut berperan penting dalam proses tersebut. Sebagai wilayah kontinen-maritim, tempat dimana energi raksasa dilepaskan melalui konveksi oleh laut, Indonesia mempunyai peranan yang penting dalam penelitian dinamika atmosfer dan ionosfer. Penelitian dinamika atmosfer dan ionosfer melalui proses kopling telah dilakukan di LAPAN dengan memanfaatkan radar MF. Beberapa metode dan analisis hasil penelitian radar MF akan dipaparkan dalam makalah ini dalam mendukung penelitian dinamika atmosfer dan ionosfer

This paper presents a statistical analysis to investigate the day-to-day variability of field-aligned irregularities (FAI) occurrence in nighttime F-region ionosphere over the Equatorial Atmosphere Radar (EAR), West Sumatra, Indonesia. FAI echoes were identified based on signal intensity of backscatter radar observations. We analyzed nighttime F-region FAI during 3 years starting in January 2011 to December 2013. For the first time, a combinatorics analysis was applied to examine the statistical likelihood of various day-to-day FAI occurrence patterns. The empirical day-to-day combinatorics analysis was performed based on binary classification of EAR observation data into either FAI occurrence (+) or absence (-) for each calendar date. Permutations of various day-to-day occurrence patterns, from 1-day to 6-day patterns, were sorted into histograms. The combinatorics analysis was performed in 4 separate time intervals to account for seasonal variation: two equinoxes (March and September) and two solstices (June and December). EAR data show that FAI occurrence probability is maximum for the two equinoxes, and that it is minimum for the two solstices. Our analysis shows that certain day-to-day patterns are more likely to occur than others, and such “combinatorics fingerprints” depend on season. During the solstices, persistent absence of FAI over several consecutive days far outweighed persistent FAI occurrence over an equivalent grouping of days with the same length. Meanwhile, during the equinoxes, we found a generally more equitable distribution between persistent day-to-day FAI occurrence and persistent day-to-day FAI absence. These findings may open new ways to help forecast FAI occurrence on a regional basis.

Perturbations of the ionosphere related to geomagnetic storms have been an object of a close attention of ionospheric researchers for several decades and therefore are relatively well known. Effects of geomagnetic storms to atmospheric parameter have been studied. Mustel et al.,(1977) summarized a decrease of pressure after strong sporadic geomagnetic storms, while Pudovkin and Veretenko (1992) summarized changes of the meridional profile of the zonal atmospheric pressure during geomagnetic strom. Recently, Gustavo A. Mansilla (2011) obtain that atmospheric parameters such as wind speed and temperature could be affected by geomagnetic storms. In this paper we examine the possible connection between neutral wind speed from Meteor Wind Radar Kototabang and intense geomagnetic storms occured in 2003 and 2004. By statistical method we compare storm time value of neutral wind speed over Kototabang with their standard deviation obtained from quiet time value. The results shows that geomagnetic storms influence neutral wind speed over Kototabang.

Salah satu teori tentang ketidakstabilan plasma lapisan E ionosfer dikaitkan dengan adanya ion-ion logam yang terakumulasi dalam suatu windshear vertikal dari angin netral ketika angin dalam arah zonal bernilai nol. Kajian mengenai mekanisme pembentukan ion-ion di lapisan E yang dikaitkan dengan windshear dari angin netral di atas Kototabang dan Pameungpeuk sangat menarik. Hal ini mengingat, selain pentingnya analisis dari densitas elektron sebagai indikator dinamika plasma, yang tidak kalah penting adalah memahami variasi kecepatan angin netral sebagai salah satu komponen yang berperan dalam dinamika plasma lapisan E tersebut. Pada penelitian sebelumnya, dinamika plasma di lapisan E diketahui dari data frekuensi kejadian E sporadis setiap bulan selama tahun 2009. Kemudian variasi angin netral diketahui dengan cara menentukan fluks momentum kecepatan angin netral menggunakan perhitungan statistik root mean square dari data kecepatan angin netral rata-rata 3 jam-an setiap bulan selama tahun 2009. Untuk pengolahhan data stasiun Kototabang, hasilnya menunjukkan bahwa proses-proses cuaca permukaan lebih dominan berperan dalam pembentukan lapisan E. sporadis dibandingkan windshear insitu. Penelitian lebih lanjut untuk melihat keterkaitan antara variasi angin netral dengan frekuensi kejadian E sporadis di atas Pameungpeuk menunjukkan hasil yang berbeda dengan hasil analisis data Kototabang, karena ternyata variasi kecepatan angin bersesuaian dengan frekuensi kejadian E sporadis selama tahun 2009, sehingga kemungkinan windshear insitu lebih banyak berperan dalam pembentukan E sporadis pada lapisan ionosfer di atas Pameungpeuk