Although we acknowledge that this particle model is more applicable to melting sleet than low-density snowflakes, it should provide insights into the effects of the initiation of the melting process on the W-band radar dark band. 52:838–851. J. Appl. Although it is possible to contrive melting snowflake models that can be applied to Rayleigh scattering to simulate such microscopic melting scenarios (Fabry and Szyrmer 1999), simulating the backscattering of these particles at optical and millimeter wavelengths is confounded by the intricacies of the melting process and the lack of a suitable theoretical approach. Optical backscattering from near-spherical water, ice and mixed phase drops. A wind tunnel investigation of the internal circulation and shape of water drops falling at terminal velocity in air. Radar Doppler : principe et fonctionnement Son principe de fonctionnement est le suivant. 1990. Lidar and Triple-Wavelength Doppler Radar Measurements of the Melting Layer: A Revised Model for Dark and Bright Band Phenomena Kenneth Sassen1, James R. Campbell2, Pavlos Kollias3, Matthew Shupe4, Christopher Williams5, and Jiang Zhu1 1. 3) was only 1.52 mm h−1, however. Les radars Doppler sont utilisés p… J. Atmos. À quoi ressemblait le réseau routier français au XVIIIe siècle ? } The absence of W- and K-band bright bands indicates that Rayleigh scattering conditions in the melting snow were violated at these wavelengths. Remote Sens. Local. Les radars à modulation de fréquence permettent, en plus, de déterminer la distance de l'objet. A wind tunnel and theoretical study of the melting behavior of atmospheric ice particles. Simpson, J., , C. Kummerow, , W. K. Tao, , and R. F. Adler. As shown in controlled laboratory ice crystal melting studies (Oraltay and Hallett 1989, 2005), under many environmental conditions meltwater initially coats ice crystal surfaces and then tends to bead up at the intersection of ice branches due to surface tension effects. 1984. Soc., 577–597. However, problems with this explanation caused by the widths of the particle size distribution and other factors were recognized in Lhermitte (2002), and the possibility that an unrepresentative temperature sounding influenced this model should also be considered. Meneghini, R., and L. Liao. This variation gives direct and highly accurate measurements of the radial component of a target's velocity relative to the radar. We begin addressing these issues in the current study based on a unique ensemble of remote sensors. width: 100%; Oraltay, R. G., and J. Hallett. We attribute the radar dark band to a combination of Rayleigh and non-Rayleigh scattering effects weighed over the particle size distribution. 3-Day Forecast. We show in Fig. J. Atmos. These wet snowflakes are nonspherical and still relatively large, which, in combination, generates strong microwave backscattering. 7 the results of concentric ice/water sphere Mie backscattering simulations for melting particles of a constant size, using the Bohren and Huffman (1998) coated-sphere code and the W-band radar ice/water refractive indices given in Sassen and Liao (1996). Today. Sassen, K. 1977b. Note that the radar dBZ scale is valid in each case for the S-band data, with the W- and K-band profiles often adjusted to compress the dynamic range of the total signals and to facilitate the data intercomparison (see figure caption). The eastern site at the Kendall-Tamiami Executive Airport (∼25 km southwest of Miami) was uniquely equipped with three Doppler radars and a radiation measurement suite that included a near-continuously operated eye-safe lidar (see Table 1 for remote sensor specifications). Kerker, M. 1969. Note that the rapid signal decrease with height in the snow aloft is due to overwhelming attenuation, which is verified by the radar data, indicating much higher cloud-top heights, and produces a lidar bright band at ∼4.5 km. The W-band radar measurements consistently failed to detect the strong backscatter enhancement that we refer to as the radar bright band, and only noted a gradual Ze increase due to the refractive index consequences of the phase change. Normalized backscattering cross sections are given for particles spanning the Rayleigh and Mie domains (see inserted total particle diameters). Much of our planet’s precipitation originates as snow far above the surface of the earth. Radar Observation of the Atmosphere. Modeling of the melting layer. In particular, while a water-coated snowflake displays increased backscattering in the Rayleigh regime, the opposite is true for larger particles due to the effects of the different refractive indices of water and ice. At the somewhat longer 0.86-cm wavelength (34.86-GHz frequency) Ka-band wavelength, the National Oceanic and Atmospheric Administration (NOAA) millimeter cloud radar (MMCR; Moran et al. 1995. Sci. Campbell et al. Satellite Radar Images. margin: 0; TRIPEx‐pol was a follow‐on campaign of the first triple‐frequency campaign (TRIPEx; Dias Neto et al., 2019) including a new X Band Doppler profiling radar with enhanced sensitivity. The same can be said of the representativeness of the available W-band radar dark-band case studies. The lidar dark bands are rather symmetrical and centered ∼100 m below the peaks in the S-band radar bright bands in both cases. In the middle is a representation of the corresponding models that an S-band radar would sense. Sassen, K., and L. Liao. Sassen, K., and T. Chen. 22:3505–3508. There are no additional pages on this site. 7:883–890. “We’re expecting to triple or quadruple our income this season,” White said. The full repertoire of backscattering phenomena was observed in the melting region, that is, the various lidar and radar dark and bright bands. Fabry, F., and I. Zawadski. Surtout, du fait de l'effet Doppler, le faisceau d'ondes aura, à son retour, une fréquence différente de la fréquence d'émission. Named after the appearance of the narrow layer of strong signals on the oscilloscope displays of World War II vintage radars, it was not long before the main causes of the bright band were identified (for reviews see Battan 1973; Dennis and Hitchfield 1990). An unattended cloud-profiling radar for use in climate research. The pendent particle shape and experimental setup (using a horizontally incident laser beam) does not provide a good model for melting snowflakes studied by zenith lidar. Sassen, K. 1977a. 1968. Strong lidar backscattering anisotropy from aerodynamically distorted raindrops has recently been reported using a scanning lidar (Roy and Bissonnette 2001). In between the two limits is a transition zone often marked by large oscillations caused by backscattering resonances. display: flex; This research was supported by NASA Grants NAG5-11503 and NAG513418, Agreement W-10041 from the CRYSTAL FACE program, NASA Grant NAG5-9753 from the TRMM program, and NSF Award ATM0296190. Live Doppler Radar covering Syracuse and Central New York. The K-band radar display sometimes indicates a comparatively weak bright band at a similar height, but only under weakly precipitating conditions. .ajtmh_container { Meteor. Meteor. The radar products are also available as OGC compliant services to use in your application. Modern weather radars are mostly pulse-Doppler radars, capable of detecting the motion of rain droplets in addition to the intensity of the precipitation. We can refer to this as the melting hail analogy, which causes non-Rayleigh (χ >∼2, or D >∼2 mm at λ=0.32 cm) ice spheres to backscatter less energy when water coated than when dry (Fig. 30.1626, doi:10.1029/2002GL016825. Le radar routier est un radar Doppler qui sert à mesurer la vitesse des véhicules en circulation. J. Atmos. Optical backscattering from near-spherical water, ice and mixed phase drops. 4a–c are 10-min-averaged MPL and Doppler radar profiles for three periods on the indicated days, showing obvious lidar dark bands. Stephens, G. L. Coauthors 2002. Oceanic Technol. Anomalous mid-atmospheric heights and persistent thunderstorm patterns over Florida. 1999) is a single-antenna version of the radar developed during the early 1980s (Lhermitte 1988). Sci. 1984) and make routine (12 hourly) sounding data unrepresentative. Meteor. 2, this corresponds to a ∼1.0–1.6-mm particle diameter increase for the W-band radar. HB100 Microwave Motion Sensor 10.525GHz Doppler Radar Detector for Arduino. A wind tunnel investigation of the internal circulation and shape of water drops falling at terminal velocity in air. Quelle est la différence entre physique et chimie ? We have identified a region of an ice cloud where a sharp transition of dual-wavelength ratio occurs at a fixed height for longer than 20 min. 1970. Corresponding Author. The term lidar dark band, in contrast to the radar bright band, delineates its quintessential property. Although we show the position of the 0°C isotherm for reference, the temperature gradient in the melting layer may be highly variable because of evaporative cooling, vertical motion, and other factors, so we choose not to provide a vertical temperature or height scale. Comparison of the triple-radar returns in the brightband region reveals significant wavelength-dependent Ze differences, as well as differences in the basic Doppler signatures. Prior to showing examples from the multiple remote sensor dataset, it is useful to overview the scattering conditions to be expected at each wavelength in the melting layer, where various Rayleigh and non-Rayleigh effects will be manifested. Almanac. Thus, as indicated here, the details of the bright/dark phenomena can vary noticeably from case to case, and our cases only represent a single geographical region and season. The latest on rain storms, snowfall, severe weather alerts and school closings This particular transmission mode, called triple-PRT, where PRT stands for Pulse Repetition Time, has the enormous advantage of allowing the measurement of the Doppler velocity unambiguously up to maximum range[1]. Precision measurement of water droplet evaporation rates. Soc. 1985. Lv002 Doppler Radar 2,6-3,3 GHz 8-15 M 5,5-36v … D. Atlas, Ed., Amer. Michaels, P. J. Thus, the radar bright band is dominated by Rayleigh dielectric scattering effects in the few largest melting snowflakes, and is not generally representative of the condition of most of the hydrometeors. Tornado Watch is in effect for northeastern North Carolina locations until 3am Friday. Thus, because the mean Doppler velocities in the Rayleigh domain are weighed according to the D6 power law, S-band microwave radar data are strongly biased toward the few largest particles, which have fallen the fastest and melted the least. A comparatively small W-band radar Ze decrease occurs high in the melting region under some conditions, corresponding to the position where mean Doppler V are just beginning to increase at all wavelengths (Fig. 40:4770–4780. The S-band radar display at the top shows a consistent radar bright band centered at ∼4.3 km height above mean sea level (MSL), whose intensity tends to vary with the rainfall rate. Thus, we are more interested in the relative variations in the radar signals than their absolute magnitudes. In contrast to the ubiquitous 10.6-cm (S band) radar bright band, only intermittent evidence is found at 0.86 cm (K band), and no clear examples of the radar bright band are seen at 0.32 cm (W band), because of the dominance of non-Rayleigh scattering effects. This is shown in Fig. 5:03. The K-band radar bright bands occur under light rainfall conditions, presumably due to the dielectric constant effect in relatively small (i.e., Rayleigh scattering) wet snowflakes. Campbell, J. R., , D. L. Hlavka, , E. J. Welton, , C. J. Flynn, , D. D. Turner, , J. D. Spinhirne, , V. S. Scott, , and I. H. Hwang. 44:206–220. Although the concentric water/ice sphere model is a poor representation for melting snowflakes (Di Girolamo et al. A relatively weak W-band radar dark band of ∼3 dBZ occurs at the top of the melting zone at 4.5 km (a ∼6 dBZ decrease is found in the example given by Lhermitte 2002), while a bright band is clearly present in the S-band radar data at 4.25 km. The University of Miami 94-GHz Doppler Cloud Radar (UMDCR; Albrecht et al. A Doppler radar is a specialized radar that uses the Doppler effect to produce velocity data about objects at a distance. Neuf. It does this by bouncing a microwave signal off a desired target and analyzing how the object's motion has altered the frequency of the returned signal. Moreover, the extent that nonspherical mixed-phase raindrop fall orientation affects the lidar melting-layer phenomena remains to be determined. Fabry, F., and W. Szyrmer. geojf@aero.obs‐mip.fr ; Laboratoire d'Aérologie, CNRS and Université Paul Sabatier, Toulouse, France. Comparison of the triple-radar returns in the brightband region reveals significant wavelength-dependent Z e differences, as well as differences in the basic Doppler signatures. Such traditional Doppler radar data show that particle fall speeds continue to increase to near the bottoms of the radar bright bands and lidar dark bands. Gaps in the data records are present for all but the S-band system. Note that the radar Ze values have been affected by wavelength-dependent backscattering and attenuation effects and system calibration uncertainties. 5 shows idealized lidar backscattering (with the generic effects of attenuation on returned power above the dark band, included as the dashed line), and W- and S-band Ze and V profiles. J. Atmos. The traditional (S band) radar brightband peak occurs low in the melting region, just above the lidar dark-band minimum. Estimation of cloud content by W-band radar. 5 reinforce these inferences, although at first glance the S-band data would seem to indicate otherwise. Because signal increases approaching the melting level from above are typically attributed to ice crystal aggregation, W-band radar dark-band effects may have counteracted this tendency in this case. An unattended cloud-profiling radar for use in climate research. 2000. Battan, L. J. Res. 1990. Meteor. 96:247–256. 15:1125–1128. Observation of rain at vertical incidence with a 94 GHz Doppler radar: An insight on Mie scattering. While not inhibiting strong convective cell development, more stratiform rainfall events were also encountered. This feature allows the instrument to be operated full time in an autonomous fashion. As stated by Lhermitte (2002), “Even after fifty years of melting-layer observations and studies in various parts of the world, we are still in need of detailed radar observations of reflectivity and Doppler velocity.. .using vertically pointing radars working at different wavelengths from 10 cm to a very short millimeter wave (3.2 mm).” The research reported here represents a step in this direction, which also fortuitously incorporated the special information from the vastly different scattering conditions encountered at the 0.523-μm lidar wavelength. Spinhirne, J. D. 1993. 27:1899–1902. Thus, until late in the process, the melting snowflake actually consists of a myriad of water coatings and irregular drop beads. D. Atlas, Ed., Amer. triple-frequency Doppler cloud radar observations Davide Ori Stefan Kneifel, Vera Schemann, José Dias Neto, Markus Karrer, Axel Seifert. Interestingly, there is an analog of the bright band with lidar, but the lidar bright band owes its existence to the increasingly strong snowflake backscattering with height coupled with the overwhelming attenuation rate in the snowfall surrounding the freezing level, which creates a feature resembling a bright band on an oscilloscope display (Sassen 1977a). Unisciel et l’Université de Lille 1 nous expliquent leur fonctionnement au cours de cet épisode de Kezako. Northeast Radar. The closest Miami radiosonde temperature profiles are given at the right (the location of 0°C is highlighted), but it should be acknowledged that the precipitation process can significantly alter the local atmospheric structure (Stewart et al. Model simulations of melting hydrometeors: A new bright band from melting frozen drops. Aerial photograph of the eastern CRYSTAL FACE field site at the Kendall-Tamiami Executive Airport near Miami, where (clockwise from the top right of the tarmac) the roof-mounted NOAA K-band Doppler radar, the NASA Surface Measurements for Atmospheric Radiative Transfer (SMART) van that held the MPL and several radiometers, the circular rain guard enclosing the NOAA S-band radar dish, and the free-standing University of Miami W-band Doppler radar attached to its supporting van are shown, Comparison of normalized backscattering cross sections (i.e., backscatter coefficients divided by particle cross-sectional areas) vs spherical water drop diameter for the three indicated radar wavelengths, showing how Mie scattering effects emerge at different drop sizes as a function of wavelength. This evidence comes from triple-wavelength Doppler spectrum radar data that were fortuitously being collected. In (b) 8 dBZ and in (c) 13 dBZ were added to the W-band radar Ze, A schematic representation of the hydrometeor shapes responsible for the various lidar and radar bright- and dark-band features of the melting layer. B. Demoz, , and D. N. Whiteman. Tonight 37° Rain to Snow? 35:932–938. Lett. These images are more or less what are actually sensed by visible wavelength lidar, where backscattering responds to the exact details of particle shape. The two cases in Figs. Characteristics through the melting layer of stratiform clouds. Eye safety is achieved by using a rapidly pulsed (2.5 KHz), low-powered (1.0 W) laser source that is expanded through a transmit–receive Cassegrain telescope. Intéressé par ce que vous venez de lire ? Doppler V are, interestingly, quite similar at the K- and S-band wavelengths. 41:3227–3237. According to Fig. Accordingly, K-band radars, with their intermediate wavelengths, may sense conditions somewhere between the S and W bands, depending on the sizes of the hydrometeors in each case. (This collapse happens when the surface tension of the accumulating liquid overwhelms the structural strength of weakened crystal branches.) The micropulse (0.523 μm) lidar (MPL; Spinhirne 1993) is a compact, eye-safe device, which is being increasingly utilized worldwide at ground-based observing sites for unattended cloud and aerosol observations. The W-band radar V profiles, which are least affected by D6 sampling effects, support the conclusion that the traditional (S band) radar bright band occurs low in the melting layer near to where many severely melted snowflakes are collapsing into raindrops (as sensed by lidar). Soc., CD-ROM, P3.18. Forfait mobile Noël 2020 : les meilleures offres à ne pas rater chez les gros opérateurs, Formation aux métiers du web : jusqu'à -89% sur ce bon plan. Such radars are traditional in the sense that pulse attenuation is rarely significant and the returned radar signals can be treated relatively simply with the Rayleigh scattering theory. height: 4px; Part II: Electromagnetic. 16:309–322. Res. Sci. Cette fréquence trahit la vitesse de l'obstacle en question. } See the latest New York Doppler radar weather map including areas of rain, snow and ice. Appl. 13WHAM ABC Rochester provides local news, weather forecasts, traffic updates, health reports, notices of events and items of interest in the community, local sports and … It was not until relatively recently that Sassen and Chen (1995) comprehensively studied this phenomenon and gave it a name. (2002) have recently described the instrument in detail and summarized the relevant MPL data processing techniques. France radars, which transmit pulses non-regularly spaced in time. Un radar Doppler est un radar qui utilise l'effet Doppler-Fizeau de l'écho réfléchi par une cible pour mesurer sa vitesse radiale. It is clear that as particle sizes increase beyond the Rayleigh and transition zones, ice particles become considerably stronger backscatterers. However, the microphysical/backscattering model that has resulted differs from previous models in some respects in both the optical and microwave domains. Atmospheric probing at the shortest 0.32-cm (94-GHz frequency) wavelength of W-band radars is sensitive to relatively small cloud droplets and ice crystals, although pulse attenuation in rain and melting snow can have noticeable effects on the returned signals. 6 in terms of Mie theory backscattering predictions for water and ice spheres tailored to the W-band radar wavelength. We hypothesize that an analogous situation occurs for snowflakes first entering above-freezing air. As shown theoretically by Battan (1973) for large melting hailstones, a water coating on large ice particles can generate a decrease in radar backscattering because of the differences in the water and ice dielectric constants and the emergence of Mie scattering effects. Soc., 98–108. Il permet ainsi une mesure directe et extrêmement précise de la composante vitesse de la cible dans l'axe du faisceau. Because of the differences in the dielectric constants between water and ice, ice particles produce much weaker backscattering and attenuation in the Rayleigh scattering regime, such that radar returns in the rain are strongly enhanced, despite the larger sizes of the low-density (iceplus-air mixture) snowflakes (Meneghini and Liao 2000), and the fact that the concentration of raindrops declines significantly because their fall speeds are much greater than the snowflakes from which they are derived. Actually, once outside the Rayleigh domain, water absorbs the incident radiation so strongly that even microscopic coatings will reduce the backscattering from the underlying ice surfaces. In contrast to the usual strong diurnal convective activity expected during midsummer months (Michaels 1985), rainfall at this time was often more continuous in nature. Unfortunately, it has yet to be determined how representative the Sassen and Chen (1995) findings are, particularly with regard to the melting-layer temperature structure, the precipitation rate and mechanism, and how measurements at other radar wavelengths compare. 2003), it may apply to conditions in the initial melting process. The minima in backscattering caused by resonances also tend to occur with similar water coatings. Le signal micro-onde émis par l'antenne directionnelle du radar est réfléchi par la cible et comparé en fréquence avec le signal original aller et retour. Lett. This report contains a summary of all the microburst-producingthunderstorms that occurred within the triple Doppler region that were scanned in a coordinated fashion, during the months ofJune, July, August, and September 1991. This corresponds to the traditional radar brightband scenario. Threat of strong to severe storms remains; damaging wind gusts and a … Geosci. The W-band Doppler V profiles in Figs. Achat immédiat +0,73 EUR (livraison) 421 vendus. Characteristics through the melting layer of stratiform clouds. Model simulations of melting hydrometeors: A new bright band from melting frozen drops. First, it should be noted that the strong optical attenuation from the comparatively large (unmelted) snowflakes in the vicinity of the freezing level helps to create a lidar bright band whose characteristics depend on the precipitation rate. 4b, a K-band radar bright band is clearly indicated, with a peak slightly below the S-band radar brightband center. Ro, P. S., , T. S. Fahlen, , and H. C. Bryant. As a consequence of our knowledge of the physics of precipitation formation, snow and rain from melting snow are believed to be the dominant processes in temperate zones, and also probably play an important role in deep convective activity worldwide. This is a brief discussion about why the Doppler Weather Radar is important to meteorologists, how it works and what types of data the radar produces. Note the corresponding kink in the W-band radar V profile in the lower melting layer, which is also indicative of a mixture of hydrometer types. Res. The subsequent collapse of these decidedly nonspherical mixed-phase particles into smaller near-spherical drops considerably reduces backscattering with a zenith radar. A wind tunnel and theoretical study of the melting behavior of atmospheric ice particles. The lidar dark band, on the other hand, is a recently recognized curiosity of melting-layer remote sensing. 2002), improving our understanding of the scattering and attenuation of microwaves in the melting layer is particularly warranted. Bohren, C. F., and D. R. Huffman. Get more local and breaking news from Triple M. ... Albany Doppler Radar Upgrade Now Complete. Oceanic Technol. Mitra, S. K., , O. Vohl, , M. Ahr, , and H. R. Pruppacher. That is, the K- and S-band radar Doppler V data are weighted toward the largest, fastest-falling raindrops, which are too large at the 0.32-cm wavelength to behave as Rayleigh scatterers, and so have a lessened impact on the mean weighted V. The unusual occurrence of the dual minima in the lidar dark band is probably a result of the presence of a mixture of ice particle fall streaks with different size or type characteristics, which can lead to multiple radar bright bands (Fabry and Zawadski 1995). This position is close to where the W-band reflectivities and Doppler velocities reach their plateaus, but is well above the height at which the S-band Vs stop increasing. As indicated in Fig. Although no evidence for a bright band is apparent in the W-band radar display, a weak radar dark band is indicated by a decline in radar signals at ∼4.5 km MSL from 1430 to 1500 UTC, where dBZ are, in contrast, increasing slightly at the other radar wavelengths (see below). 7 indicates that the snowflake size distribution has a large impact on the strength of the W-band radar dark band, explaining why this phenomenon is not consistently observed in the melting layer. The idealized vertical V profiles in Fig. J. Roy. 83:1771–1790. The most widely recognized remote sensing feature observed during the melting of snowflakes is the radar bright band. VI: Experiment and theory for snow flakes. A 3-PRT scheme is prone to dealiasing errors that mainly depend on: 4b, indicating that the rain shower was in the process of descending or that raindrop evaporation was occurring. Pruppacher, H. R., and K. Beard. At right are idealized vertical profiles of radar Ze and V for W- (dashed) and S-band (solid) radar. Post, , R. A. Kropfli, , D. C. Welsh, , and K. B. Widener. Weather Map Gallery. Le radar Doppler est un radar dont le fonctionnement repose sur l'effet Doppler. Strong dependence of rain-induced lidar depolarization on the illumination angle: Experimental evidence and geometrical-optics interpretation. The NWS radar site including permanent installations of X, Ka, and,! Alaska Fairbanks, AK 99775 ro, P. E. Johnston,, D. Welsh... Anomalous mid-atmospheric heights and persistent thunderstorm patterns over Florida cell development, more stratiform Rainfall events were also encountered analogous. 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Triple-Frequency Doppler cloud radar observations Davide Ori Stefan Kneifel, Vera Schemann, Dias... From triple doppler radar distorted raindrops has recently been reported in demoz et al this. Field research is still disclosing new aspects of the scattering and attenuation effects get detailed, weather. Models that an analogous situation occurs for snowflakes first entering above-freezing air plus, de déterminer la distance l'objet... The advent of weather radar from top to bottom data records are present for all but the S-band data seem! Véhicules en circulation nos lecteurs radar site including permanent installations of X, Ka, and band... Velocities also show a steady increase descending through the melting of ice crystals: new... Mesurer la vitesse d'un objet figure 1 shows an triple doppler radar photograph of the capabilities of the radial of. Are present for all but the S-band system not inhibiting strong convective cell development, more stratiform Rainfall were... 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The surface tension of the particles that show this effect in the first example the! ( TRMM ) Université Paul Sabatier, Toulouse, France ils ne permettent de déterminer distance... S-Band wavelengths reality Discontinuous conversions of properties aggregation riming riming example from Seifert Beheng! The peaks in the rain and melting zones radar analysis of the Instruments deployed at the millimeter W- K-band! A wind tunnel and theoretical study of the corresponding models that an analogous situation occurs for snowflakes entering...

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