Auroral precipitation fading before and at substorm onset: ionospheric and geostationary signatures

Rapid fading of auroral activity a few minutes before substorm breakup has earlier been analyzed in case-studies. Here we report on a study in which all-sky camera (ASC) and magnetic data over 3 years were examined to find breakups that were accompanied by a preceding fading. To illustrate typical features of the fading effect we analyze three events in detail and discuss seven other events to find the spatial and temporal behavior of the fading and the global conditions favoring this phenomenon, which is not associated with every breakup. In these ten events the precipitation diminished typically for about 2 min and a local breakup followed after 2–3 min. Usually the arc which broke up had faded earlier. Comparison with geostationary electron flux recordings shows that in many cases the global onset had already taken place when the fading was recorded at a different longitude. Thus fading is not just a growth-phase phenomenon as often thought, but can also appear as a precursor of the approaching auroral bulge. The AE index and solar-wind data reveal that the fading has a tendency to take place during magnetically disturbed conditions caused by continuous energy input from the solar wind. Furthermore, while a widely recognized phenomenon, we have found that the fading prior to breakup is not a very common feature in the spatio-temporal scale of auroral ASC recordings. In many cases the deepness of the fading had a longitudinal dependence, which leads to the suggestion that this phenomenon is related to azimuthal gradients in the tail magnetic field and/or plasma pressure. Possible scenarios causing fading both before and after the onset are discussed based on a few previously presented theoretical auroral-arc models.     

First results from the plasma composition spectrometer PROMICS-3 in the Interball project

PROMICS-3 is a plasma experiment flown in the Russian project Interball. It performs three-dimensional (3D) measurements of ions in the energy range 4 eV–70 keV with mass separation and of electrons in the energy range 12 eV–35 keV. The Interball project consists of two main satellites, the Tail Probe and the Auroral Probe, each with one subsatellite. The Interball Tail Probe was launched on 3 August 1995, into a 65° inclination orbit with apogee at about 30 R_E. Both main satellites carry identical PROMICS-3 instruments and thus direct comparisons of the particle distributions will be possible once the Auroral Probe is launched. Furthermore, PROMICS-3-Tail is the first instrument measuring the 3D ion distribution function in the magnetospheric boundary layers at high latitudes. In this paper we describe the PROMICS-3 instrument and show initial results from the Tail probe, measurements of the mag-netosheath, plasma sheet, and ring current plasmas.     

A case study of airborne and satellite remote sensing of a spring bloom event in the Gulf of Finland

The concentrations of chlorophyll-a (chl-a), total suspended solids (TSS) and the absorption coefficient of colored dissolved organic matter (a_CDOM(400)) are estimated in Case II waters using medium resolution imaging spectrometer (MERIS) satellite (full resolution [FR] level 1b, 300 m resolution) and AISA airborne spectrometer data acquired during a spring bloom in the Gulf of Finland, Baltic Sea on April 27, 2004. The accuracy of the estimation is analyzed using empirical band-ratio algorithms together with in situ observations that include water samples analyzed in a laboratory (variation ranges: 22–130 μg/l, 2.9–20 mg/l, and 1.29–2.61 m⁻¹ for chl-a, TSS and a_CDOM(400), respectively). Additional in situ estimates (transects) on these characteristics are available through absorption and scattering coefficients measured with an ac-9 absorption and attenuation meter installed in a flow-through system. The retrieval accuracy (R²) of all three water quality characteristics with MERIS data is close to or above 0.9, while the RMSE is 7.8 μg/l (22%), 0.74 mg/l (16%) and 0.08 m⁻¹ (5%), for chl-a, TSS and a_CDOM(400), respectively. The validity of the chl-a algorithm is tested using nine additional data points. The BIAS-error for these points is 5.2 μg/l and the RMSE is 10.6 μg/l. The effects of changes in the atmospheric characteristics on band-ratio algorithms in cases where no concurrent in situ reference data are available are analyzed using the MODerate spectral resolution atmospheric TRANSmittance algorithm and computer model (MODTRAN). The additional error due to these changes is estimated to be below 20% for the applied ratio algorithms. The water quality data available in the level 2 MERIS-product distributed by the European Space Agency did not include valid results for the date investigated here.     

Diversity of murtoos and murtoo-related subglacial landforms in the Finnish area of the Fennoscandian Ice Sheet

Murtoos are recently discovered triangular-shaped subglacial landforms that form under warm-based ice and in association with significant subglacial meltwater flow. They appear in distinct fields and commonly occur in the area that was covered by the Fennoscandian Ice Sheet during glacial periods. Murtoos potentially represent a transition form from non-channelized to channelized subglacial drainage networks. In the present study, we analyse and classify murtoos and murtoo-related landforms in the Finnish area of the Fennoscandian Ice Sheet based on their characteristics and appearance in LiDAR-based digital elevations models. Combined with morphometric analyses, the observations suggest that five types of murtoos and murtoo-related landforms are common and widespread in Finland: (i) triangle-type murtoos (TTMs), (ii) chevron-type murtoos (CTMs), (iii) lobate-type murtoos (LTMs), (iv) murtoo-related ridges and escarpments (MREs), and (v) other murtoo-related polymorphous landforms (PMRs) that look like small mounds and ridges. The morphometric characteristics of the different types are described here in detail, and it is shown that they are spatially and geomorphologically related. In addition, we provide examples of murtoos other than the TTMs to demonstrate that different murtoo types and murtoo-related landforms are composed of similar sediments and architectural characteristics. The diversity of murtoo landforms and the transition between distinct murtoo types indicate rapid and complicated variations in the configuration of subglacial hydrology at different spatial and temporal scales. This study emphasizes the essential role of subglacial meltwater in the shaping of glacial landscapes and the redistribution of large volumes of sediments during the deglaciation of the Fennoscandian Ice Sheet.     

Single-station narrowband ranging of active storm cells without lightning-type discrimination

We present a statistical technique for ranging the edges of active storms cell using a very simple narrowband receiver tuned to 1 MHz (the MW band in radio, just below HF frequencies). We show that a principle based on the “30–30 rule” can be used to define practical warning levels. From the measurements carried out in Finland, we show that the narrowband source intensities of cloud-to-ground lightning vary log-normally; this results in a ranging uncertainty of about 20%, which can be reduced if a suitable floating average is used. Based on one storm, we suggest that the differences between intra-cloud and ground-to-cloud signals at 1 MHz are small enough to make an IC–CG discrimination. Eliminating such a discrimination allows all lightning impulses to be used in the range and improves the accuracy, since more flashes are then available as inputs into the distance-estimation algorithm. Although the system is only validated against a single storm, we provide definitions by which this and other narrowband detectors could be independently verified; existing narrowband devices have not been verified in this manner, due in part to a lack of such standardized definitions.     

First results from the hot plasma instrument PROMICS-3 on Interball-2

The PROMICS-3 instrument on Interball-2 is nominally identical to the PROMICS-3 instrument on Interball-1. It performs three-dimensional measurements of ions in the energy range 4 eV–70 keV with mass separation and of electrons in the energy range 300 eV–35 keV. Interball-2 was launched on August 29, 1996, into an orbit with the same inclination as that of Interball-1, 63°, but with apogee at 20 000 km. In this study the PROMICS-3 instrument on Interball-2 is briefly described and examples of the first results are presented. Firstly, we report observations of upward moving molecular ions with energies of up to 700 eV at the poleward edge of the auroral oval. Previous observations of outflowing molecular ions have been at lower altitudes and lower energies. Secondly, we show observations of dawnside magnetosheath plasma injections. Using conjugate data from both PROMICS-3 instruments we have found dispersion structures above the morningside auroral oval, which occurred simultaneously with isolated “pockets” of magnetosheath plasma at a distance of X_GSM = −14 to −12 R_E, which had been injected into the inner part of the low-latitude boundary layer. These isolated plasma structures were sites of strong field-aligned currents and are proposed to be the magnetospheric counterparts of the dispersion structures.     

Cyclic evolution of sunspots: Gleaning new results from old data

The records of sunspot number, sunspot areas and sunspot locations gathered over the centuries by various observatories are reanalysed with the aim of finding as yet undiscovered connections between the different parameters of the sunspot cycle and the butterfly diagram. Preliminary results of such interrelationships are presented.     

PRELIMINARY STUDY ON THE INFLUENCE OF FY-4 LIGHTNING DATA ASSIMILATION ON PRECIPITATION PREDICTIONS

Data from the lightning mapping imager on board the Fengyun-4 meteorological satellite (FY-4) were used to study the assimilation of lightning data and its influence on precipitation predictions. We first conducted a quality control check on the events observed by the first Fengyun-4 satellite (FY-4A) lightning mapping imager, after which the noise points were removed from the lightning distribution. The subsequent distribution was more consistent with the spatial distribution and range of ground-based observations and precipitation. We selected the radar reflectivity, which was closely related to the lightning frequency, as the parameter to assimilate the lightning data and utilized a large sample of lightning frequency and radar reflectivity data from the eastern United States provided by Vaisala. Based on statistical analysis, we found the empirical relationship between the lightning frequency and radar reflectivity and established a look-up table between them. We converted the lightning event data into radar reflectivity data and found that the converted reflectivity and composite reflectivity of ground-based radar observations showed high consistency. We further assimilated the lightning data into the model, adjusted the model cloud analysis process and adjusted the model hydrometeor field by using the lightning data. A rainstorm weather process that occurred on August 8, 2017, in south China was used for the numerical forecast experiment, and three experiments were designed for comparison and analysis: a control experiment, an experiment without the assimilation of FY-4 lightning data (NoLig), and an experiment with the assimilation of FY-4 lightning data (Lig). The results show that after assimilating the FY-4A lightning data, the accuracies of the intensity, central location and range of the precipitation predicted by the Lig experiment were obviously superior to those predicted by the control and NoLig experiments, and the effect was especially obvious in the short-term (1–2 hour) forecast. The studies in this paper highlight the application value and potential of FY-4 lightning data in precipitation predictions.     

Climate change impacts on forest fire potential in boreal conditions in Finland

The aim of this work was to study the forest fire potential and frequency of forest fires under the projected climate change in Finland (N 60°–N 70°). Forest fire index, generally utilized in Finland, was used as an indicator for forest fire potential due to climatological parameters. Climatic scenarios were based on the A2 emission scenario. According to the results, the forest fire potential will have increased by the end of this century; as a result of increased evaporative demand, which will increase more than the rise in precipitation and especially in southern Finland. The annual number of forest fire alarm days is expected to increase in southern Finland to 96–160 days by the end of this century, compared to the current 60–100 days. In the north, the corresponding increase was from 30 to 36 days. The expected increase in the annual frequency of forest fires over the whole country was about 20% by the end of this century compared to the present day. The greatest increase in the frequency of fires, per 1,000 km², was in the southernmost part of the country, with six to nine fires expected annually per 1,000 km² at the end of this century, meaning a 24–29% increase compared to the present day frequencies.     

A three-parameter magnitude phase function for asteroids

We develop a three-parameter H, G₁, G₂ magnitude phase function for asteroids starting from the current two-parameter H, G phase function. We describe stochastic optimization of the basis functions of the magnitude phase function based on a carefully chosen set of asteroid photometric observations covering the principal types of phase dependencies. We then illustrate the magnitude phase function with a chosen set of observations. It is shown that the H, G₁, G₂ phase function systematically improves fits to the existing data and considerably so, warranting the utilization of three parameters instead of two. With the help of the linear three-parameter phase function, we derive a nonlinear two-parameter H, G₁₂ phase function, and demonstrate its applicability in predicting phase dependencies based on small numbers of observations.