The ionospheric condition and GPS positioning performance during the 2013 tropical cyclone Usagi event in the Hong Kong region

Detecting Ionospheric Irregularity Based on ROT Variation Using Android Devices Cloud System

Global navigation satellite system (GNSS) precise positioning performance will be strongly affected under severe ionospheric anomaly conditions. The combination of multi‐GNSS can increase the available observations and improve the geometry of continuously tracked satellites. This paper focuses on assessing the positioning performance with the combination of Global Positioning System (GPS), Global'naya Navigatsionnaya Sputnikova Sistema (GLONASS), and BeiDou System (BDS) around the St. Patrick's Day geomagnetic storm (9–18 March) in 2015 in Hong Kong. The rate of total electron content (TEC) index (ROTI) indicates severe ionospheric anomalies before the superstorm, while it was absent during the main phase of the storm in Hong Kong. Furthermore, strong scintillation events on signal‐to‐noise ratio (SNR) and multipath (MP) observables are observed during ionospheric anomalies period. Then the performance of single‐point positioning (SPP) and precise point positioning (PPP) with multi‐GNSS is shown. The ionospheric scintillation events may reduce pseudorange accuracy but affect SPP performance a little in this study, while the PPP accuracy is vastly decreased due to the subsequent reconvergence caused by frequent cycle slip (CS). Compared to PPP solutions with GPS only, the accuracy is improved significantly with the combination of multi‐GNSS.

Adaptability of GPS/BDS broadcast ionospheric models to solar activities

This study investigates the performance of three different signal combinations (L1-L2, L1-L5, and L2-L5) for estimating ionospheric total electron content (TEC) and the rate of TEC (ROT) using Quasi-Zenith Satellite System (QZSS) observations over the Korean Peninsula. GNSS data collected from nine stations across the Korean Peninsula were analyzed for the period from Day of Year (DOY) 1 to 182 in 2024. Differential Code Bias (DCB) was estimated for QZSS satellites, showing high temporal stability with daily variations within ±0.3 ns. The TEC values derived from three different signal combinations were compared with the CODE Global Ionospheric Map (GIM). Compared to other combinations, the L1-L5 pair shows the closest agreement with the CODE GIM, yielding a mean bias of +0.25 TEC units (TECU) with a root mean square (RMS) of 3.59 TECU. In addition, the ROT analysis over the consecutive six days revealed that the L1-L5 combination consistently exhibited the lowest RMS values of about 0.027 TECU compared to other signal pairs. As a result, we suggest that the L1-L5 combination can provide better performance for QZSS-based ionospheric monitoring and TEC studies.

This paper presents a new cycle slip detection and repair method using Total Electron Content Rate (TECR) information derived from individual satellite dual-frequency data of a single Global Positioning System (GPS) receiver while pseudorange measurements are subject to arbitrarily large range errors. Sudden Increase of Pseudorange Error (SIPE), similar to cycle slips in nature, is quite common in various data acquisition scenarios. The basic principle of this method is to take advantage of the fact that the ionospheric TECR does not exceed certain threshold, which is set as 0.35 TECU/s in this study. Analytic expressions to evaluate the effect of SIPE on cycle slip detections have been developed. The search spaces for cycle slip candidate pairs are defined, given a predefined (sufficiently large) SIPE value. Two cycle slip validation rules are proposed to validate the cycle slip candidates. Over 99.9% of candidates can be rejected with the application of two validation rules. The theoretically maximal number of remaining cycle slip candidate pairs (NRCP) can be exactly calculated based on the magnitude of SIPE, TECR threshold, and the data sampling interval. After applying validation rules, the correct cycle slip pairs can be identified using a modified low-order polynomial fitting method. This method is tested on 13 high rate (1-Hz) dual-frequency datasets recorded by both ground-based static and satellite-borne high dynamic GPS receivers under various levels of ionospheric activities. Simulated cycle slips in 12 different possible cases and varying SIPE magnitudes are introduced into the data sets. In each test scheme, averagely 600–750 pairs of cycle slips are simulated. The SIPE magnitudes are set to vary from 50.0 m to 1000.0 m. Test results show that all the cycle slips in all the test schemes and all the datasets have been successfully detected and fixed even with a maximum SIPE of 1000.0 m in pseudoranges. A distinct advantage of this method is that it works in real-time with individual satellite’s data from a single dual-frequency receiver, even if the carrier phases have virtually any size of cycle slips and the pseudoranges have virtually arbitrarily large errors.

Major Tropical Cyclone (TC) events cause extensive damage in coastal regions of the western North Atlantic Basin. The short instrumental record leaves significant gaps in understanding long‐term trends in TC recurrence and intensity, creating uncertainty about future storm trends. Analysis of an ∼520‐year core record from Harvey Lake, located >80 km from the Atlantic coast in southwestern New Brunswick, Canada was carried out using: (a) end‐member mixing analysis (EMMA) of lake sediment grain size data to identify storm‐linked sedimentological processes; and (2) ITRAX X‐ray fluorescence (XRF) derived element/ratios (Fe, Ti, Ca/Sr, Zr/Rb, K/Rb, and Br + Cl/Al) associated with precipitation, weathering, catchment runoff, and air masses. Three derived end members were correlated to heavy rainfall events (EM01), spring freshet (EM02), and TCs (EM03). CONISS analysis of the EMMA and XRF core data resulted in recognition of four unique climatic zones distinguished by distinct distributions of TC and rainfall/weathering/runoff/and air masses. Numerous, major (EM01) rainfall events and (EM03) TC events characterized the basal core record during the early Little Ice Age (LIAa; Zone 1) phase, terminating at ∼1645. A near cessation of heavy rainfall and TC events differentiated the subsequent colder LIAb (∼1645–1825; Zone 2) and subsequent Little Ice Age Transition (∼1825–1895; Zone 3). A resurgence of major rainfall and TC events occurred during recovery from the LIA starting in ∼1895 (Zone 4). EMMA provides a robust tool for recognition of TC and major rainfall events, and greatly expands the potential for paleo‐storm activity research well inland from coastal regions.

Earth’s atmospheric layers are subjected to continuous changes in near-earth space. Hence, the space weather needs to be investigated, and the most reliable method is using satellite system. Widely used technique is Global Positioning System (GPS) which is primarily designed for tracking and navigation. Ionosphere, one of the earth’s atmospheric layers which contains free electrons, is highly affected by space weather like solar flares, geomagnetic storms and seasons. Since the GPS satellite signal travels through the ionosphere, its propagation is affected, and signal gets delayed by plasma of free electron known as total electron content (TEC). TEC not only depends on space weather but also on geographic location, specially the low latitude region (23° above and below the equator). Indian subcontinent falls under this low latitude region, and hence, satellite system applications like precise positioning, navigation, tracking and satellite communication are affected. Hence to correct the GPS delay, accurate estimation of TEC is necessary. In this paper, TEC and rate of TEC (ROT) are calculated, and the variation of the TEC is analyzed. The ionospheric delay, TEC and ROT are calculated for GPS data received on March 10, 2013, from the dual-frequency GPS receiver of NovAtel make located in K L University, Guntur, India (Lat: 16.44° N/Long: 80.62° E). The analysis presented in this paper will help in precise estimation of composition of ionosphere which will improve navigational accuracy.

In precise point positioning (PPP), the ionospheric delay is corrected in a first-order approximation from GPS dual-frequency observations, which should eliminate almost completely the ionosphere as a source of error. However, sudden plasma density variations can adversely affect the GPS signal, degrading accuracy and reliability of positioning techniques. The occurrence of plasma density irregularities is frequent at equatorial latitudes and is reflected in large total electron content (TEC) variations. We study the relation between large changes in the rate of TEC (ROT) and positioning errors in single-epoch PPP. At equatorial latitudes and during post-sunset hours, the estimated altitudes contain errors of several meters for a single-epoch position determination, and latitude and longitude estimates are also degraded. These results have been corroborated by the online CSRS-PPP (NRCan) program. Moreover, abrupt changes in the satellite geometry have been discarded as possible cause of such errors, suggesting an apparent relation between the occurrence of large ROT and degraded position estimates.

This study cross-validates the radar reflectivity Z, the rainfall drop size distribution parameter (median volume diameter, Do ) and the rainfall rate R estimated from the Tropical Rainfall Measuring Mission (TRMM) satellite Precipitation Radar (PR), a combined PR and TRMM Microwave Imager (TMI) algorithm (COM) and a C-band dual-polarised ground-radar (GR) for TRMM overpasses during the passage of tropical cyclone (TC) and non-TC events over Darwin, Australia. Two overpass events during the passage of TC Carlos and eleven non-TC overpass events are used in this study and the GR is taken as the reference. It is shown that the correspondence is dependent on the precipitation type whereby events with more (less) stratiform rainfall usually have a positive (negative) bias in the reflectivity and the rainfall rate whereas in the Do the bias is generally positive but small (large). The COM reflectivity estimates are similar to the PR but it has a smaller bias in the Do for most of the greater stratiform events. This suggests that combining the TMI with the PR adjusts the Do towards the "correct" direction if the GR is taken as the reference. Moreover, the association between the TRMM estimates and the GR for the two TC events, which are highly stratiform in nature, is similar to that observed for the highly stratiform non-TC events (there is no significant difference) but it differs largely from that observed for the majority of the highly convective non-TC events.

The results of raw GNSS data recorded using a Xiaomi Mi 8 android smartphone equipped with a dual-frequency GNSS module BCM47755 capable of receiving and processing signals from the GPS, Galileo, QZSS systems in the L1 and L5 frequency sub-bands are presented in the paper. The indices of ionospheric activity that as variations in the relative slant total electron content, the rate of total electron content, the rate of total electron content index, root-mean-square deviation of relative slant total electron content on the base of raw GNSS data are calculated. A comparison study of the data obtained with the data from the KZN2 station of the International GNSS Service network, equipped with a professional GNSS receiver of a geodetic class is carried out. It is shown that the median value of signal strength at frequencies L1 and L5 for the data obtained from the satellites G08, G10, G27, G32, E09 on the Xiaomi Mi 8 smartphone is ≈ 5-25% lower than data from the KZN2 station. The indices of ionospheric activity registered by the Xiaomi Mi 8 smartphone have a higher signal-to-noise ratio in comparison with the data of the KZN2 station. Median levels of variations of the relative slant TEC, ROT, ROTI, and RMSTEC obtained by the Trimble Alloy receiver at KZN2 station were 45÷70% lower than that for the Xiaomi Mi 8 smartphone. Nonetheless, the possibility of registering the indices of ionospheric activity such as relative slant total electron content and others based on dual-frequency raw GNSS measurements (primarily carrier-phase and pseudorange) of GNSS signals received by smartphones opens up prospects for attracting as wide a community as possible for collecting GNSS data and monitoring the ionosphere.

A fast algorithm for automatic detection of ionospheric disturbances: DROT

An experimental Warn-on-Forecast System (WoFS) ensemble data assimilation (DA) and prediction system at 1-km grid spacing is developed and tested using two landfalling tropical cyclone (TC) events, one springtime severe thunderstorm event, and one summertime flash flood event. To evaluate the impact of DA at 1-km grid spacing, two experiments are conducted. One experiment, namely, the WoFS-1km, generates 3-h ensemble forecasts from the 1-km WoFS analyses while another experiment, namely, the Downscaled-1km, generates 3-h ensemble forecasts from downscaled 3-km analyses. With 1-km DA, the two landfalling TC events and the summertime event show some improvement in predicting high reflectivity, while the springtime event performs worse. Meanwhile, WoFS-1km is slightly better at predicting heavier precipitation (>20 mm h−1) with lower bias. However, heavy precipitation spatial placement error is only mitigated in one TC event and the summertime event with 1-km DA but is neutral or worse in the other two events. Object-based verification for rotation objects indicates that WoFS-1km performs better in one of the TC events, but worse in the springtime event with lower probability of detection and higher false alarm ratio due to fewer strong rotation objects being generated. The forecast skill of WoFS-1km for the springtime event is degraded mainly because the convective cores do not sufficiently develop as the forecast advances. The conditional benefits from 1-km DA in this study highlights the need for evaluation of a larger sample of convective storm cases and further development of the system.

Ninety five tropical cyclonic events (tropical storms, depressions and cyclones) between 2001 and 2010 were studied to determine their impact on dust outbreaks and long-range transport over the northern Indian Ocean and south Asia. In addition to the winter and summer Shamal Winds, tropical cyclones are an important mechanism of dust entrainment and transport of dust in this region. Elevated dust levels were observed in the northern Arabian Sea during most tropical cyclone events. During the study period, fifteen tropical cyclones migrated close to the dust source areas leading to major dust storms. Anti-clockwise winds associated with these storms were observed to entrain dust and transport it mostly towards the west or south-westerly direction. Tropical cyclones and storms, located further away from dust source areas, significantly alter the dispersal pathways of dust plumes raised by other mechanisms. The Northern Bay of Bengal cyclone events are shown to aid advection of dust plumes from southwest Asia and Thar Desert over highly populated regions of the Indian Subcontinent. Tropical cyclones also play an important role in dispersal of fine-mode aerosols over South Asia and formation of complex aerosol-dust mixtures.

The global ionospheric storm in March 2015 was investigated by using data from over 3000 GPS stations worldwide. In this study, total electron content (TEC), rate of TEC (ROT), and ROT's standard deviation rate of the TEC index, as well as the second‐order difference operator TECT, were considered as main characteristic methods to distinguish ionosphereic disturbances. The results show that (1) based on the multiple methods above, we all observed that for the first time, there were three equatorward traveling ionospheric disturbances (TIDs) in the main phase of this storm. In North America, the disturbance zone expanded to ~40°N; the disturbance periods and AE peak stages were roughly synchronous. We suggest that these three TIDs were induced by the propagation of atmospheric gravity waves to low latitudes under the action of AE. (2) The most intense positive storm occurred over South America and the South Atlantic (over 300% enhancement; 00:00–05:00 UT on 18 March), whereas a negative storm was observed in the corresponding region of the Northern Hemisphere. Such inverse hemispheric asymmetry in intensity and structure can be explained by the variations of the thermospheric composition, the IMF By component, and the geomagnetic intensity. (3) On 18 March, a negative storm dominated globally (except at certain low latitudes), and tended to propagate equatorward and decay with time, which could be largely attributed to the storm circulation theory. And the evolution of the negative storm was further characterized by the foF2 variations of ionosondes.

Pulsars’ signals reaching the atmosphere can be considered being stable under certain assumptions. In such a case the ionosphere remains the main factor distorting signal from the extraterrestrial sources, particularly if we observe them at long radio waves. In this article we present the results of the analysis of relative peak flux changes for two selected pulsars: PSR J0332+5434 (B0329+54) and PSR J1509+5531 (B1508+55), observed with the long radio wave sensor (The PL612 Low Frequency Array (LOFAR) station in Bałdy), together with the analysis of Rate of TEC (ROT) parameter changes measured with the Global Navigation Satellite Systems (GNSS) sensor (IGS LAMA station (IGS: International GSSN Service)). The main objective of the work is to find if the rapid plasma density (observed with the Rate of Total Electron Content (TEC)) has a counterpart in the pulsar observation characteristics. This focuses the attention on ionosphere influence during pulsar investigations at low radio frequencies. Additionally, what was the aim of this work, our results give reasons for using pulsar signals from LOFAR together with GNSS data as multi instrumental ionosphere state probes. Our results show a clear anti-correlation between the ROT and the pulsar profile’s peak flux trends.