A giant thunderstorm on Saturn FISCHER, G; KURTH, W. S; DELCROIX, M ...
Nature (London),
07/2011, Volume:
475, Issue:
7354
Journal Article
Peer reviewed
Lightning discharges in Saturn's atmosphere emit radio waves with intensities about 10,000 times stronger than those of their terrestrial counterparts. These radio waves are the characteristic ...features of lightning from thunderstorms on Saturn, which last for days to months. Convective storms about 2,000 kilometres in size have been observed in recent years at planetocentric latitude 35° south (corresponding to a planetographic latitude of 41° south). Here we report observations of a giant thunderstorm at planetocentric latitude 35° north that reached a latitudinal extension of 10,000 kilometres-comparable in size to a 'Great White Spot'-about three weeks after it started in early December 2010. The visible plume consists of high-altitude clouds that overshoot the outermost ammonia cloud layer owing to strong vertical convection, as is typical for thunderstorms. The flash rates of this storm are about an order of magnitude higher than previous ones, and peak rates larger than ten per second were recorded. This main storm developed an elongated eastward tail with additional but weaker storm cells that wrapped around the whole planet by February 2011. Unlike storms on Earth, the total power of this storm is comparable to Saturn's total emitted power. The appearance of such storms in the northern hemisphere could be related to the change of seasons, given that Saturn experienced vernal equinox in August 2009.
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DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The Martian limb (that is, the observed 'edge' of the planet) represents a unique window into the complex atmospheric phenomena occurring there. Clouds of ice crystals (CO2 ice or H2O ice) have been ...observed numerous times by spacecraft and ground-based telescopes, showing that clouds are typically layered and always confined below an altitude of 100 kilometres; suspended dust has also been detected at altitudes up to 60 kilometres during major dust storms. Highly concentrated and localized patches of auroral emission controlled by magnetic field anomalies in the crust have been observed at an altitude of 130 kilometres. Here we report the occurrence in March and April 2012 of two bright, extremely high-altitude plumes at the Martian terminator (the day-night boundary) at 200 to 250 kilometres or more above the surface, and thus well into the ionosphere and the exosphere. They were spotted at a longitude of about 195° west, a latitude of about -45° (at Terra Cimmeria), extended about 500 to 1,000 kilometres in both the north-south and east-west directions, and lasted for about 10 days. The features exhibited day-to-day variability, and were seen at the morning terminator but not at the evening limb, which indicates rapid evolution in less than 10 hours and a cyclic behaviour. We used photometric measurements to explore two possible scenarios and investigate their nature. For particles reflecting solar radiation, clouds of CO2-ice or H2O-ice particles with an effective radius of 0.1 micrometres are favoured over dust. Alternatively, the plume could arise from auroral emission, of a brightness more than 1,000 times that of the Earth's aurora, over a region with a strong magnetic anomaly where aurorae have previously been detected. Importantly, both explanations defy our current understanding of Mars' upper atmosphere.
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In this paper, we discuss the numerical problems posed by the previously reported LInear-predictive Multi-input Equalization (LIME) algorithm when dealing with dereverberation of long room transfer ...functions (RTF). The LIME algorithm consists of two steps. First, a speech residual is calculated using multichannel linear prediction. The residual is free from the room reverberation effect but it is also excessively whitened because the average speech characteristics have been removed. In the second step, LIME estimates such average speech characteristics to compensate for the excessive whitening. When multiple microphones are used, the speech characteristics are common to all microphones whereas the room reverberation differs for each microphone. LIME estimates the average speech characteristics as the characteristics that are common to all the microphones. Therefore, LIME relies on the hypothesis that there are no zeros common to all channels. However, it is known that RTFs have a large number of zeros close to the unit circle on the z-plane. Consequently, the zeros of the RTFs are distributed in the same regions of the z-plane and, if an insufficient number of microphones are used, the channels would present numerically overlapping zeros. In such a case, the dereverberation algorithm would perform poorly. We discuss the influence of overlapping zeros on the dereverberation performance of LIME. Spatial information can be used to deal with the problem of overlapping zeros. By increasing the number of microphones, the number of overlapping zeros decreases and the dereverberation performance is improved. We also examine the use of cepstral mean normalization for post-processing to reduce the remaining distortions caused by the overlapping zeros
Lightning storms in Saturn’s atmosphere can last for a few days up to several months. In this paper we analyze a lightning storm that raged for seven and a half months at a planetocentric latitude of ...35° south from the end of November 2007 until mid-July 2008. Thunderstorms observed by the Cassini spacecraft before this time were characterized by a single convective storm region of ~2000 km in size, but this storm developed two distinct convective storm cells at the same latitude separated by ~25° in longitude. The second storm cell developed in March 2008, and the entire two-cell convective system was moving with a westward drift velocity of about 0.35 deg per day, which differs from the zonal wind speed. An exhaustive data analysis shows that the storm system produced ~277000 lightning events termed Saturn electrostatic discharges (SEDs) that were detected by Cassini’s Radio and Plasma Wave Science (RPWS) instrument, and they occurred in 439 storm episodes. We analyzed the SED intensity distributions, the SED polarization, the burst rates, and the burst and episode durations. During this storm Cassini made several orbits around Saturn and observed the SEDs from all local times. A comparison with optical observations shows that SEDs can be detected when the storm is still beyond the visible horizon. We qualitatively describe this so-called over-the-horizon effect which is thought to be due to a temporary trapping of SED radio waves below Saturn’s ionosphere. We also describe the first occurrence of so-called SED pre- and post-episodes, which occur in a limited frequency range around 4 MHz separated from the main episode. Pre- and post-episodes were mostly observed by Cassini located at local noon, and should be a manifestation of an extreme over-the-horizon effect. Combined radio and imaging observations suggest that some decreases in SED activity are caused by splitting of the thunderstorm into a bright cloud and a dark oval.
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The performance of automatic speech recognition is severely degraded in the presence of noise or reverberation. Much research has been undertaken on noise robustness. In contrast, the problem of the ...recognition of reverberant speech has received far less attention and remains very challenging. In this paper, we use a dereverberation method to reduce reverberation prior to recognition. Such a preprocessor may remove most reverberation effects. However, it often introduces distortion, causing a dynamic mismatch between speech features and the acoustic model used for recognition. Model adaptation could be used to reduce this mismatch. However, conventional model adaptation techniques assume a static mismatch and may therefore not cope well with a dynamic mismatch arising from dereverberation. This paper proposes a novel adaptation scheme that is capable of managing both static and dynamic mismatches. We introduce a parametric model for variance adaptation that includes static and dynamic components in order to realize an appropriate interconnection between dereverberation and a speech recognizer. The model parameters are optimized using adaptive training implemented with the expectation maximization algorithm. An experiment using the proposed method with reverberant speech for a reverberation time of 0.5 s revealed that it was possible to achieve an 80% reduction in the relative error rate compared with the recognition of dereverberated speech (word error rate of 31%), and the final error rate was 5.4%, which was obtained by combining the proposed variance compensation and MLLR adaptation.
We examine Saturn's atmospheric dynamics with observations in the visible range from ground-based telescopes and Hubble Space Telescope (HST). We present a detailed analysis of observations acquired ...during 2018 obtaining drift rates of major meteorological systems from the equator to the north polar hexagon. A system of polar storms that appeared in the planet in March 2018 and remained active with a complex phenomenology at least until September is analyzed elsewhere (Sánchez-Lavega et al., 2019). Many of the regular cloud features visible in 2018 are long-lived and can be identified in Saturn images in 2017, and in some cases, for up to a decade using also Cassini ISS images. Without considering the polar storms, the most interesting long-lived cloud systems are:
i) A bright white spot in the Equatorial Zone that can be tracked continuously since 2014 with minimal changes in its zonal velocity, which was 444.3 ± 3.1 m s−1 in 2014 and 452.4 ± 1.7 m s−1 in 2018. This velocity is remarkably different from the zonal winds at the cloud level at its latitude during the Cassini mission, and is closer to zonal winds obtained at the time of the Voyagers flybys and to zonal winds from Cassini VIMS infrared images of the lower atmosphere.
ii) A large long-lived Anticyclone Vortex, here AV, that formed after the Great White Spot of 2010–2011. This vortex has changed significantly in visual contrast, drift rate and latitude with minor changes in size over the last years.
iii) A system of subpolar vortices at latitudes 60–65°N present at least since 2011. These vortices and additional atmospheric features here studied follow drift rates consistent with zonal winds obtained by Cassini.
We also present a study of the positions of the vertices of Saturn's north polar hexagon from 2015 to 2018. These measurements are compared with previous analyses during the Cassini mission (2007–2014), observations with HST in the 90s, and data from the Voyagers in 1980–1981 to explore the long-term variability of the hexagon's drift rate. We find variations in the drift rate of the hexagon through these epochs that can not be fit by seasonal changes in the polar area. Instead, the different drift rates reinforce the role of the North Polar Spot that was present in the Voyager epoch and in the early 90s to cause a faster drift rate of the hexagon at that time compared with the current slower one.
•We follow long-lived atmospheric systems in Saturn one year after Cassini.•Amateur, HST and Cassini observations are combined to extend the study in time.•Fast features in the Equatorial Zone move differently to the zonal winds.•A mid-latitude and several polar vortices are studied over 8 years.•We present non-seasonal variations of the hexagon's drift rate over 40 years.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Rap1 transduces nerve growth factor (NGF)/tyrosine receptor kinase A (TrkA) signaling in early endosomes, leading to sustained activation of the p44/p42 mitogen-activated protein kinases (MAPK1/2). ...However, the mechanisms by which NGF, TrkA and Rap1 are trafficked to early endosomes are poorly defined. We investigated trafficking and signaling of NGF, TrkA and Rap1 in PC12 cells and in cultured rat dorsal root ganglion (DRG) neurons. Herein, we show a role for both microtubule- and dynein-based transport in NGF signaling through MAPK1/2. NGF treatment resulted in trafficking of NGF, TrkA and Rap1 to early endosomes in the perinuclear region of PC12 cells where sustained activation of MAPK1/2 was observed. Disruption of microtubules with nocodazole in PC12 cells had no effect on the activation of TrkA and Ras. However, it disrupted intracellular trafficking of TrkA and Rap1. Moreover, NGF-induced activation of Rap1 and sustained activation of MAPK1/2 were markedly suppressed. Inhibition of dynein activity through overexpression of dynamitin (p50) blocked trafficking of Rap1 and the sustained phase of MAPK1/2 activation in PC12 cells. Remarkably, even in the continued presence of NGF, mature DRG neurons that overexpressed p50 became atrophic and most (>80%) developing DRG neurons died. Dynein- and microtubule-based transport is thus necessary for TrkA signaling to Rap1 and MAPK1/2.
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BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UILJ, UKNU, UL, UM, UPUK
Despite the low prevalence of each rare disease, the total burden is high. Patients with rare diseases encounter numerous barriers, including delayed diagnosis and limited access to high-quality ...treatments. In order to tackle these challenges, the European Commission launched the European Reference Networks (ERNs), cross-border networks of healthcare providers and patients representatives. In parallel, the aims and structure of these ERNs were translated at the federal and regional levels, resulting in the creation of the Flemish Network of Rare Diseases. In line with the mission of the ERNs and to ensure equal access to care, we describe as first patient pathways for systemic sclerosis (SSc), as a pilot model for other rare connective and musculoskeletal diseases. Consensus was reached on following key messages: 1. Patients with SSc should have multidisciplinary clinical and investigational evaluations in a tertiary reference expert centre at baseline, and subsequently every three to 5 years. Intermediately, a yearly clinical evaluation should be provided in the reference centre, whilst SSc technical evaluations are permissionably executed in a centre that follows SSc-specific clinical practice guidelines. In between, monitoring can take place in secondary care units, under the condition that qualitative examinations and care including interactive multidisciplinary consultations can be provided. 2. Patients with early diffuse cutaneous SSc, (progressive) interstitial lung disease and/or pulmonary arterial hypertension should undergo regular evaluations in specialised tertiary care reference institutions. 3. Monitoring of patients with progressive interstitial lung disease and/or pulmonary (arterial) hypertension will be done in agreement with experts of ERN LUNG.
Purpose
The ocular and visual problems in Down syndrome are due to refractive errors, poor accomodation, strabismus, keratoconus, cataract, optic disc and retinal structural anomalies and brain ...changes. Pulmonary hypertension (PH) is associated with high mortality and morbidity and ocular complications may occur. PH associated central serous choroidopathy‐like maculopathy, venous thrombosis and neovascular glaucoma have been described in case reports but no large studies of ocular complications are available. Improved non‐invasive imaging with optical coherence tomography (OCT), enhanced depth OCT and OCT angiography without dye allow a detailed study of the retinal and optic disc changes.
Methods
A cross sectional study of 180 adult patients with PH included 9 Down patients with congenital heart disease. Age of the Down patients was 25–44 years. The fundus changes included PH associated and Down associated anomalies.
Results
PH associated mild changes included episcleral and retinal vein dilation and a thick choroid. None of the Down patients had severe complications of PH. The Down associated fundus changes included absence of optic disc cup, supranumerary optic cisc vessels,and structura lmacular anomalies with small capillary free zone. Two eyes were functionally lost due to complications of hydrops keratoconus.
Conclusions
Non‐invasive imaging with OCT allows a detailed analysis of fundus changes in Down patients with or without PH.
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BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UILJ, UKNU, UL, UM, UPUK
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