High-resolution fire danger forecast for Poland based on the Weather Research and Forecasting Model

Due to climate change and associated longer and more frequent droughts, the risk of forest fires increases. To address this, the Institute of Meteorology and Water Management implemented a system for forecasting fire weather in Poland. The Fire Weather Index (FWI) system, developed in Canada, has been adapted to work with meteorological fields derived from the high-resolution (2.5 km) Weather Research and Forecasting (WRF) model. Forecasts are made with 24- and 48-h lead times. The purpose of this work is to present the validation of the implemented system. First, the results of the WRF model were validated using in situ observations from ∼70 synoptic stations. Second, we used the correlation method and Eastaugh\u27s percentile analysis to assess the quality of the FWI index. The data covered the 2019 fire season and were analysed for the whole forest area in Poland. Based on the presented results, it can be concluded that the FWI index (calculated based on the WRF model) has a very high predictive ability of fire risk. However, the results vary by region, distance from human habitats, and size of fire

Ionospheric indices GIX and SIDX as proxies to characterize spatial and temporal ionospheric perturbations degree

Severe space weather events cause perturbations of the ionospheric plasma that, consequently, strongly affect the availability, continuity and accuracy of Global Navigation Satellite Systems (GNSS) signals and their application in telecommunication and navigation systems. With the purpose of assuring reliable information on space weather conditions and, in particular, on the perturbation degree of the ionosphere, the German Aerospace Center has developed the Gradient Ionospheric indeX (GIX) and the Sudden Ionospheric Disturbance indeX (SIDX) as proxies capable of estimating spatial and temporal perturbations degree of the ionosphere without the necessity to include historical data in the analysis.With our work, we present an overview about the performance of GIX and SIDX for characterizing spatial and temporal ionospheric perturbations in the framework of the Coordinated Ionospheric Study of Scales and Indices (CISSI) initiative, within the scientific activities of the Committee on Space Research (COSPAR). Namely, we report on the outcomes achieved with these approaches when applying them to GNSS datasets acquired over Europe and South America during selected periods of stormy and quiet geomagnetic conditions. Moreover, we examine the scientific potential of these ionospheric perturbation indices and discuss their applicability in space weather services

Ionospheric indices GIX and SIDX for the regional characterization of ionospheric perturbations degree

The total electron content (TEC) measured along different satellite-receiver links is strongly sensitive to severe spatial gradients and rapid changes in the ionosphere. Therefore, key information on space weather conditions and, in particular, on the perturbation degree of the ionosphere is crucial to assure stable and reliable services using Global Navigation Satellite Systems (GNSS) signals. By using dual-frequency GNSS measurements, the German Aerospace Center has developed the Gradient Ionospheric indeX (GIX) and the Sudden Ionospheric Disturbance indeX (SIDX) as proxies capable of estimating spatial and temporal perturbations degree of the ionosphere instantaneously, without the necessity to include historical data in the analysis. We present our advances for characterizing spatial and temporal ionospheric perturbations by utilizing GIX and SIDX in the framework of the Coordinated Ionospheric Study of Scales and Indices (CISSI) initiative, within the scientific activities of the Committee on Space Research (COSPAR). Namely, we report on the outcomes achieved with these approaches when applying them to GNSS datasets acquired over Europe and South America during a stormy and a quiet period of geomagnetic activity in 2015 (Day of Year 75-78 and 142-145, respectively). Moreover, we examine the scientific potential of these ionospheric perturbation indices at different GNSS configurations, latitudinal zones and distance ranges, and discuss their applicability in space weather services

Improved Empirical Coefficients for Estimating Water Vapor Weighted Mean Temperature over Europe for GNSS Applications

Development of the so-called global navigation satellite system (GNSS) meteorology is based on the possibility of determining a precipitable water vapor (PWV) from a GNSS zenith wet delay (ZWD). Conversion of ZWD to the PWV requires application of water vapor weighted mean temperature ( T m ) measurements, which can be done using a surface temperature ( T s ) and its linear dependency to the T m . In this study we analyzed up to 24 years (1994–2018) of data from 49 radio-sounding (RS) stations over Europe to determine reliable coefficients of the T m − T s relationship. Their accuracy was verified using 109 RS stations. The analysis showed that for most of the stations, there are visible differences between coefficients estimated for the time of day and night. Consequently, the ETm4 model containing coefficients determined four times a day is presented. For hours other than the primary synoptic hours, linear interpolation was used. However, since this approach was not enough in some cases, we applied the dependence of T m − T s coefficients on the time of day using a polynomial (ETmPoly model). This resulted in accuracy at the level of 2.8 ± 0.3 K. We also conducted an analysis of the impact of this model on the PWV GNSS. Analysis showed that differences in PWV reached 0.8 mm compared to other commonly used models

Spatio-Temporal Validation of GNSS-Derived Global Ionosphere Maps Using 16 Years of Jason Satellites Observations

Existing ionospheric models perform very well in mapping the calm state of the ionosphere. However, the problem is accurately determining the total electron content (TEC) for disturbed days. Knowledge of the exact electron density is essential for single−frequency receivers, which cannot eliminate the ionospheric delay. This study aims to investigate temporal and spatial variability in the distribution of TEC based on differences between maps of individual Ionospheric Associated Analysis Centers (IAACs) of the International GNSS Service (IGS) and aligned altimetry−TEC from 2005–2021. Based on the temporal distribution, we have observed a significant effect of solar activity on the mean and standard deviation behavior of the differences between global ionospheric maps (GIMs) and Jason−derived TEC. We determined the biases for the entire calculation period, through which it can be concluded that the upcg-Jason and igsg-Jason differences have the lowest standard deviation (±1.81 TECU). In addition, the temporal analysis made it possible to detect annual, semi−annual, and 117-day oscillations occurring in the Jason−TEC data, as well as 121-day oscillations in the GIMs. It also allowed us to analyze the potential sources of these cyclicities, solar and geomagnetic activity, in the case of the annual and semi−annual periodicities. When considering spatial variations, we have observed that the most significant average differences are in the intertropical areas. In contrast, the smallest differences were recorded in the southern hemisphere, below the Tropic of Capricorn (23.5°S). However, the slightest variations were noted for the northern hemisphere above the Tropic of Cancer (23.5°N). Our research presented in this paper allows a better understanding of how different methods of GNSS TEC approximation affect the model’s accuracy

Assessment of the Impact of GNSS Processing Strategies on the Long-Term Parameters of 20 Years IWV Time Series

Advanced processing of collected global navigation satellite systems (GNSS) observations allows for the estimation of zenith tropospheric delay (ZTD), which in turn can be converted to the integrated water vapour (IWV). The proper estimation of GNSS IWV can be affected by the adopted GNSS processing strategy. To verify which of its elements cause deterioration and which improve the estimated GNSS IWV, we conducted eight reprocessings of 20 years of GPS observations (01.1996–12.2015). In each of them, we applied a different mapping function, the zenith hydrostatic delay (ZHD) a priori value, the cut-off angle, software, and the positioning method. Obtained in such a way, the ZTD time series were converted to the IWV using the meteorological parameters sourced from the ERA-Interim. Then, based on them, the long-term parameters were estimated and compared to those obtained from the IWV derived from the radio sounding (RS) observations. In this paper, we analyzed long-term parameters such as IWV mean values, linear trends, and amplitudes of annual and semiannual oscillations. A comparative analysis showed, inter alia, that in terms of the investigation of the IWV linear trend the precise point positioning (PPP) method is characterized by higher accuracy than the differential one. It was also found that using the GPT2 model and the higher elevation mask brings benefits to the GNSS IWV linear trend estimation

A new index for statistical analyses and prediction of travelling ionospheric disturbances

Travelling Ionospheric Disturbances (TIDs) are signatures of atmospheric gravity waves (AGWs) observed in changes in the electron density. The analysis of TIDs is relevant for studying coupling processes in the thermosphere–ionosphere system. A new TID index ATID is introduced, which is based on an easy extension of the commonly used approach for TID detection. This TID activity index, which can be applied for individual Global Navigation Satellite Systems (GNSS) stations and also for mapping TID activity, is capable to study both Large Scale TIDs (LSTIDs) and Medium Scale TIDs (MSTIDs). ATID is well applicable for statistical analyses and investigations of the source mechanisms of TIDs. Correlation studies presented here reveal that LSTID magnitudes at mid-latitudes are well correlated with solar wind derived parameters, like the Kan-Lee merging electric field (EKL), the intermediate function (EWAV) and the modified version of the Akasufo ϵ parameter (ϵ3). Thus, the magnitude of the global solar-wind energy input into the Earth’s magnetosphere–ionosphere–thermosphere system is most relevant for the LSTID generation. The correlation with common geomagnetic activity indices shows that also sudden changes in the magnetosphere–ionosphere–thermosphere system are relevant. Good correlation results are limited to mid-latitudes. High-latitude regions are impacted by auroral processes and low-latitude regions by coupling from below and other instabilities. ATID can be used for the modelling and prediction as demonstrated with a prediction model for storm induced LSTIDs, based on solar wind observations only. Very good performance of this LSTIDs prediction model in mid-latitudes has been proven

Efficient Usage of Dense GNSS Networks in Central Europe for the Visualization and Investigation of Ionospheric TEC Variations

The technique of the orthogonal projection of ionosphere electronic content variations for mapping total electron content (TEC) allows us to visualize ionospheric irregularities. For the reconstruction of global ionospheric characteristics, numerous global navigation satellite system (GNSS) receivers located in different regions of the Earth are used as sensors. We used dense GNSS networks in central Europe to detect and investigate a special type of plasma inhomogeneities, called travelling ionospheric disturbances (TID). Such use of GNSS sensors allows us to reconstruct the main TID parameters, such as spatial dimensions, velocities, and directions of their movement. The paper gives examples of the restoration of dynamic characteristics of ionospheric irregularities for quiet and disturbed geophysical conditions. Special attention is paid to the dynamics of ionospheric disturbances stimulated by the magnetic storms of two St. Patrick’s Days (17 March 2013 and 2015). Additional opportunities for the remote sensing of the ionosphere with the use of dense regional networks of GNSS receiving sensors have been noted too

Regional characterization of ionospheric perturbations degree with GIX and SIDX

Ionospheric perturbations deteriorate the accuracy, integrity, availability and continuity of precise and safety-of-life Global Navigation Satellite Systems (GNSS) applications. Therefore, a reliable characterization of the spatial gradients and rapid changes in the total electron content (TEC) is crucial in order to mitigate their impact. With this aim, we present here the results achieved by using dual-frequency GNSS measurements for estimating the Gradient Ionospheric indeX (GIX) and the Sudden Ionospheric Disturbance indeX (SIDX) over Europe and South America. The advantage of these two index approaches is their capability to estimate the spatial and temporal perturbation degree of the ionosphere instantaneously without statistical analyses of historical data. Our dataset covers two periods of 2015 with contrasting geomagnetic activity selected in the framework of the Coordinated Ionospheric Study of Scales and Indices (CISSI) initiation within the COSPAR-related International Space Weather Action Team (ISWAT) G2B-04. The first period covers the St. Patrick Day storm (DoY 75-78) and the second period covers a period of geomagnetically quiet conditions (DoY 142-145). Our estimate of GIX for the quiet days shows a regular pattern of diurnal variation with values of less than 10 milliTECU/km. On the contrary, the gradient values during the perturbed period are enhanced by several times, reaching values of more than 30 milliTECU/km over stormy conditions. By computing GIX at different horizontal scales, we find that the higher values of gradients are obtained for the shorter ranges (e.g. 30-250 km) rather than for larger scales (e.g. 50-500 km). This agrees with essentially stronger smoothing over longer distances. Also, by considering ionospheric piercing points (IPPs) at three different latitude ranges over Europe, our estimates of GIX show different behavior that depend on the propagation mechanism of ionospheric storms. This is also valid for SIDX which is sensitive to rapid temporal changes of the ionospheric ionization, e.g. initiated by solar flares or particle precipitation events. We further discuss the potential of the ionospheric indices GIX and SIDX for GNSS positioning applications and space weather services

The impact of initial and boundary conditions on severe weather event simulations using a high-resolution WRF model. Case study of the derecho event in Poland on 11 August 2017

Precise simulations of severe weather events are a challenge in the era of changing climate. By performing simulations correctly and accurately, these phenomena can be studied and better understood. In this paper, we have verified how different initial and boundary conditions affect the quality of simulations performed using the Weather Research and Forecasting Model (WRF). For our analysis, we chose a derecho event that occurred in Poland on 11 August 2017, the most intense and devastating event in recent years. High-resolution simulations were conducted with initialization at 00 and 12 UTC (11 August 2017) using initial and boundary conditions derived from the four global models: Global Forecast System (GFS) from the National Centers for Environmental Prediction (NCEP), Integrated Forecast System (IFS) developed by the European Center for Medium-Range Weather Forecasts (ECMWF), Global Data Assimilation System (GDAS) and ERA5. For the last, we made separate calculations using data at the pressure and model levels. The results were evaluated against surface and radar data. We found that the simulations that used data from the GDAS and GFS models at 12 UTC were the more accurate, while ERA5 gave the worst predictions. However, all models were characterized by a low probability of detection and a high number of false alarms for simulations of extreme precipitation and wind gusts