Top PDF Use of radio occultation to probe the high latitude ionosphere

Use of radio occultation to probe the high latitude ionosphere

Use of radio occultation to probe the high latitude ionosphere

quite low considering late recovery phase of the storm. However, there was additional solar wind activity on this day, clearly indicated by a proton density increase at approx- imately 01:00 UT. This did not lead to a geomagnetic storm in the classic sense (Dst decrease), but did cause significant auroral currents as indicated by AE. We speculate here that the fluctuating interplanetary magnetic fields led to precipitation occurring at

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An evaluation of COSMIC radio occultation data in the lower atmosphere over the Southern Ocean

An evaluation of COSMIC radio occultation data in the lower atmosphere over the Southern Ocean

Sokolovskiy et al. (2006) demonstrated the usefulness of using global positioning system (GPS) radio occultation (RO) data to study the ABL height. They found that es- timating the ABL height from the refractivity profile pro- vided good agreement with radiosonde and reanalysis data sets. Most commonly used methods for determining the ABL height from GPS RO data involve identifying large gradients in the refractivity profile (Ao et al., 2012; Basha and Ratnam, 2009). A global analysis of ABL heights was performed by Guo et al. (2011) from GPS RO data. Their technique in- volved looking for a break point, or first-order discontinu- ities, in the refractivity profile, which served as an indicator of the ABL top. It was shown to agree well with boundary layer heights estimated from high-resolution radiosonde ob- servations, particularly in the subtropical high-pressure re- gions where there is often a well-defined decrease in mois- ture above the main inversion. Chan and Wood (2013) use a similar technique to study the global variability of the ABL height. The authors find good agreement of ABL heights be- tween COSMIC and radiosonde data on seasonal timescales. Similarly, Seidel et al. (2010) present a climatology of ABL heights using several methods to estimate the heights
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First assimilations of COSMIC radio occultation data into the Electron Density Assimilative Model (EDAM)

First assimilations of COSMIC radio occultation data into the Electron Density Assimilative Model (EDAM)

Abstract. Ground based measurements of slant total electron content (TEC) can be assimilated into ionospheric models to produce 3-D representations of ionospheric electron den- sity. The Electron Density Assimilative Model (EDAM) has been developed for this purpose. Previous tests using EDAM and ground based data have demonstrated that the informa- tion on the vertical structure of the ionosphere is limited in this type of data. The launch of the COSMIC satellite con- stellation provides the opportunity to use radio occultation data which has more vertical information. EDAM assimila- tions have been run for three time periods representing quiet, moderate and disturbed geomagnetic conditions. For each run, three data sets have been ingested – only ground based data, only COSMIC data and both ground based and COS- MIC data. The results from this preliminary study show that both ground and space based data are capable of improving the representation of the vertical structure of the ionosphere. However, the analysis is limited by the incomplete deploy- ment of the COSMIC constellation and the use of auto-scaled ionosonde data. The first of these can be addressed by re- peating this type of study once full deployment has been achieved. The latter requires the manual scaling of ionosonde data; ideally an agreed data set would be scaled and made available to the community to facilitate comparative testing of assimilative models.
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Generation of a Bending Angle Radio Occultation Climatology    (BAROCLIM) and its use in radio occultation retrievals

Generation of a Bending Angle Radio Occultation Climatology (BAROCLIM) and its use in radio occultation retrievals

gle (Fig. 3) is error dominated above 80 km. Therefore we combined the mean bend- ing angles with a priori information to generate a model that is useful also above the mesosphere. A priori information profiles can be obtained from already existing clima- tological models or profile data sets. Current state-of-the-art analysis, reanalysis, or forecast products from NWP centers do not reach high enough in the atmosphere (the

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Radio occultation bending angle anomalies during tropical cyclones

Radio occultation bending angle anomalies during tropical cyclones

for Meteorology, Ionosphere and Climate (COSMIC) six-satellite constellation (Anthes et al., 2008), and the Gravity Recovery And Climate Experiment (GRACE) twin satel- lites (Beyerle et al., 2005), have a denser number of measurements at mid and high latitude due to the inclination of the orbits, but they do not provide a good coverage of the tropical area (Fig. 1). A new advanced GPS receiver is planned to be launched in

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A study of Traveling Ionospheric Disturbances and Atmospheric Gravity Waves using EISCAT Svalbard Radar IPY-data

A study of Traveling Ionospheric Disturbances and Atmospheric Gravity Waves using EISCAT Svalbard Radar IPY-data

Abstract. We present a statistical study of Traveling Iono- spheric Disturbances (TIDs) as observed by the EISCAT Svalbard Radar (ESR) during the continuous IPY-run (March 2007–February 2008) with field-aligned measurements. We have developed a semi-automatic routine for searching and extracting Atmospheric Gravity Wave (AGW) activity. The collected data shows that AGW-TID signatures are common in the high-latitude ionosphere especially in the field-aligned ion velocity data (244 cases of AGW-TID signatures in daily records), but they can be observed also in electron density (26 cases), electron temperature (12 cases) and ion temper- ature (26 cases). During the IPY campaign (in solar mini- mum conditions) AGW-TID events appear more frequently during summer months than during the winter months. It re- mains still as a topic for future studies whether the observed seasonal variation is natural or caused by seasonal variation in the performance of the observational method that we use (AGW-TID signature may be more pronounced in a dense ionosphere). In our AGW-TID dataset the distribution of the oscillation periods has two peaks, one around 0.5–0.7 h and the other around 1.1–1.3 h. The diurnal occurrence rate has a deep minimum in the region of magnetic midnight, which might be partly explained by irregular auroral activity ob- scuring the TID signatures from our detection routines. As both the period and horizontal phase speed estimates (as de- rived from the classical AGW dispersion relation) show val- ues typical both for large scale TIDs and mesoscale TIDs it is difficult to distinguish whether the generator for high- latitude AGW-TIDs resides typically in the troposphere or in the near-Earth space. The results of our statistical analysis give anyway some valuable reference information for the fu- ture efforts to learn more about the dominating TID source
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Excitation of twin-vortex flow in the nightside high-latitude ionosphere during an isolated substorm

Excitation of twin-vortex flow in the nightside high-latitude ionosphere during an isolated substorm

study. The data employed were from radars funded by the re- search funding agencies of Canada, France, the UK, and USA. We would also like to thank Dr Mike Ruohoniemi of the Johns Hopkins University Applied Physics Laboratory for provision of the Map-Potential algorithm software. For the ground magne- tometer data, we thank the Finnish Meteorological Institute and its co-institutes who maintain the IMAGE magnetometer array, the Canadian Space Agency who constructed and maintain the CANO- PUS instrument array, the Geological Survey of Canada (Natu- ral Resources Canada) for use of data from its magnetometer ar- ray, Boston University, Augsburg College, the University of Al- berta and the Geological Survey of Canada who run the MACCS magnetometer array (which is supported by the National Science Foundation’s Magnetospheric Physics Program), and Ian Mann and David Milling for the SAMNET data. SAMNET is a PPARC Na- tional Facility deployed and operated by the University of York. We would also like to thank Howard Singer and the National Oceanic and Atmospheric Administration for GOES-8 magnetic field data, Geoff Reeves and the Los Alamos National Laboratory for LANL particle data, Norman Ness and Charles Smith for provision of ACE magnetometer data, and David McComas for provision of ACE SWEPAM data. AG was supported during this study by a PPARC Quota Studentship, and SWHC by PPARC Senior Fel- lowship PPA/N/S/2000/00197. SuperDARN studies and opera- tions at the University of Leicester are supported by PPARC grants PPA/G/O/1999/00181 and PPA/R/R/1997/00256 respectively.
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The impact of large scale ionospheric structure on radio occultation retrievals

The impact of large scale ionospheric structure on radio occultation retrievals

Abstract. We study the impact of large-scale ionospheric structure on the accuracy of radio occultation (RO) retrievals. We use a climatological model of the ionosphere as well as an ionospheric data assimilation model to compare quiet and geomagnetically disturbed conditions. The presence of ionospheric electron density gradients during disturbed con- ditions increases the physical separation of the two GPS fre- quencies as the GPS signal traverses the ionosphere and at- mosphere. We analyze this effect in detail using ray-tracing and a full geophysical retrieval system. During quiet con- ditions, our results are similar to previously published stud- ies. The impact of a major ionospheric storm is analyzed using data from the 30 October 2003 “Halloween” super- storm period. At 40 km altitude, the refractivity bias under disturbed conditions is approximately three times larger than quiet time. These results suggest the need for ionospheric monitoring as part of an RO-based climate observation strat- egy. We find that even during quiet conditions, the magnitude of retrieval bias depends critically on assumed ionospheric electron density structure, which may explain variations in previously published bias estimates that use a variety of as- sumptions regarding large scale ionospheric structure. We quantify the impact of spacecraft orbit altitude on the magni- tude of bending angle and retrieval error. Satellites in higher altitude orbits (700+ km) tend to have lower residual biases due to the tendency of the residual bending to cancel between the top and bottomside ionosphere. Another factor affecting accuracy is the commonly-used assumption that refractive in- dex is unity at the receiver. We conclude with remarks on the implications of this study for long-term climate monitoring using RO.
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Comparison of ionospheric radio occultation CHAMP data with IRI 2001

Comparison of ionospheric radio occultation CHAMP data with IRI 2001

To study the latitudinal and local time dependence of the difference, the data set has been divided into three parts rep- resenting high (|φ|>60 ◦ ), medium (30 ◦ <|φ|<60 ◦ ) and low latitude (|φ|<30 ◦ ) ranges. These data sets are subdivided in 4 groups corresponding to different local times (night: 21:00–03:00 LT, morning: 03:00–09:00 LT, day: 09:00– 15:00 LT, evening: 15:00–21:00 LT) as it is shown in Fig. 3. The mean deviation of the plasma frequency fp is gener- ally less than 1.6 MHz (σ =1.4 MHz) at high and less than 1.5 MHz (σ =1.9 MHz) at mid- latitudes under day-time con- ditions above 300 km height. Surprisingly the corresponding bias reaches only 1.1 MHz (σ =2.1 MHz) at low latitudes. It is difficult to comment this low latitude result because en- tire IRO derived electron density profiles have not yet been validated sufficiently for this latitude range. We are aware of the fact that the spherical symmetry assumption in IRO retrievals is violated in particular in the crest region due to strong horizontal gradients of the electron density distribu- tion and therefore errors cannot be excluded. As expected, due to the enhanced ionization and variability at low lati- tudes in the evening hours, the bias and the dispersion reach high values in the order of 2 and 2.5 MHz, respectively. In the lower ionosphere (100–150 km height) bias and disper- sion values are principally smaller than the corresponding F2 layer values. The smallest bias is found at low latitudes at day-time with 0.3 MHz (σ =1.9 MHz) whereas the biggest value is found also at low latitudes in the evening hours with 1.9 MHz (σ =1.9 MHz).
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Imaging of structures in the high-latitude ionosphere: model comparisons

Imaging of structures in the high-latitude ionosphere: model comparisons

imaging ionospheric features at high latitudes. The method replicates well the horizontal structures in the ionisation, though the lack of horizontal ray paths in satellite-to-ground geometry results in greater uncer- tainty in the imaging of the vertical pro®le. The present results show that the quadratic programming method used here has been able to reproduce most of the essential features of the vertical structure of the ionisation, including the situation when there is an underlying auroral-E layer over only a limited latitudi- nal extent of the image. The discrepancies in the densities around the F2 layer peak are generally less than 10%, while di€erences in peak height are close to the limit set by the pixel resolution. The departures in pro®le shape in the high topside between model input and the reconstructed image can be attributed to the limitation imposed on the current work by the use in the quadratic programming method of only Chapman-type pro®les. Modi®cations to the method to incorporate a wider range of possible vertical ionospheric pro®les in the high topside could result in better agreement in that region. Improvements in the reproduction of the density at the peak of the layer would also be expected from this change. In essence, the tomographic method redistrib- utes the line integral of the density, the total electron content, throughout the pro®le, so that small discrep-
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Empirical analysis and modeling of errors of atmospheric profiles from GPS radio occultation

Empirical analysis and modeling of errors of atmospheric profiles from GPS radio occultation

The RO processing starts with precise orbit determination and atmospheric excess phase processing at both GPS fre- quencies. Knowledge of atmospheric excess phase profiles as a function of time allows the calculation of Doppler shift. Involvement of precise orbit information yields bending an- gle profiles as a function of impact parameter. The main ionospheric contribution of the measurement is removed by a linear combination of two bending angles, derived for both GPS frequencies separately. In the upper stratosphere and above, the signal-to-noise ratio of the measurement declines resulting in large bending angle noise at these altitudes. However, the inverse Abel transform, which is used to calcu- late refractivity from bending angle, requires data knowledge at highest altitudes. Noisy and erroneous bending angles cause non-negligible errors in the refractivity profile, which are then further transported downward by the hydrostatic in- tegral in the pressure and temperature profiles. For noise re- duction at high altitudes, raw bending angle profiles are ini- tialized with background data leading to optimized bending angle profiles (note that raw bending angles are assimilated in numerical weather prediction systems). An Abel inversion of the ionosphere-corrected, initialized bending angle profile gives a refractivity profile as a function of altitude. Neglect- ing the moist contribution of refractivity in a so-called “dry air retrieval” yields atmospheric dry density profiles. Dry pressure profiles as a function of altitude, geopotential height profiles as a function of dry pressure altitude, and dry tem- perature profiles as a function of altitude are then calculated using the hydrostatic equation and the equation of state.
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Application of the locality principle to radio occultation studies of the Earth's atmosphere and ionosphere

Application of the locality principle to radio occultation studies of the Earth's atmosphere and ionosphere

Highly stable signals synchronized by atomic frequency standards and radiated by GPS satellites at frequencies F1 = 1575.42 MHz and F2 = 1227.60 MHz create at the al- titudes from 0 to 20 000 km radio fields that can be used for the development of the RO method as a new tool for global monitoring of the ionosphere and neutral atmosphere (Gur- vich and Krasilnikova, 1987; Yunck, 1988). Several LEO missions were launched during 1995–2014 for the study of the atmosphere and ionosphere: GPS/MET (Melbourne et al., 1994; Ware et al., 1996; Gorbunov et al., 1996; Kursinski et al., 1997; Vorob’ev et al., 1997; Hajj and Romans, 1998), SAC-C (Schmidt et al., 2005), CHAMP (Wickert et al., 2001, 2009), FORMOSAT-3 (Liou et al., 2007; Fong et al., 2008), GRACE (Hajj et al., 2004; Wickert et al., 2005), METOP (Von Engeln et al., 2011; Joo et al., 2012), TERRA-SAR, TANDEM-X (Zus et al., 2014), and FY-3 CNOS (Bai et al., 2014). The success of these missions demonstrated that the RO technique is a powerful remote sensing tool for obtaining key vertical profiles of bending angle, refractivity, tempera- ture, pressure and water vapour in the atmosphere and elec- tron density in ionosphere with global coverage, high spatial and temporal resolution (Zhang et al., 2013). Explicit anal- ysis of experimental data of LEO missions introduced im- portant contributions in the following areas: (i) the theory of radio wave propagation (Gorbunov and Gurvich, 1998a; Gorbunov et al., 2002; Benzon et al., 2003; Gorbunov and Lauritsen, 2004; Gorbunov and Kirchengast, 2005; Pavelyev et al., 2004, 2010a); (ii) climate changes detection (Kirchen- gast et al., 2000; Steiner et al., 2001; Foelsche et al., 2008); (iii) space weather effects and ionosphere monitoring (Rius et al., 1998; Jakowski et al., 2004; Wickert et al., 2004; Ar- ras et al., 2008, 2010); (iv) deriving new radio-holographic methods of the RO remote sensing (Karayel and Hinson,
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The Impact of the Expansion of the Bolsa Familia Program on the Time Allocation of Youths And Their Parents Lia Chitolina Miguel Nathan Foguel Naercio Menezes-Filho

The Impact of the Expansion of the Bolsa Familia Program on the Time Allocation of Youths And Their Parents Lia Chitolina Miguel Nathan Foguel Naercio Menezes-Filho

This paper evaluates the impact of the 2007 expansion of the Bolsa Família program to families with youths aged 16 to 17 years (entitled Benefício Variável Jovem) on the time allocation of youths and on the labor supply of their parents. A differences-in-differences intention to treat estimator was used to compare households among the poorest 20 per cent with 16 years old youths with households in the same income bracket with 15 years old adolescents before and after the expansion. The results show that granting the benefit had a positive and significant impact on school attendance, helping bridge 25% of the gap in school attendance between rich and poor households, and on the decision of young people to study and work at the same time. The effects on school attendance were stronger for males and when the child was the youngest in the household. No impacts were found on the parents ’ labor supply.
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50 MHz continuous wave interferometer observations of the unstable mid-latitude E-region ionosphere

50 MHz continuous wave interferometer observations of the unstable mid-latitude E-region ionosphere

structured in Doppler velocity (or Doppler shift), with the positive and negative Doppler bands coming from zonally adjacent echoing regions separated by a few kilometers. Both Doppler bands move as an entity across the radar beam with a speed near 50 m/s which means they associate with one and the same unstable plasma region. This situation, which is observed regularly in our data, is in contradiction with the notion of isotropic plasma turbulence characterizing type 2 echoes, a fact that has been pointed out before in a paper by Hussey et al. (1999). This option, of course, does not exclude the possibility that the gradient drift instability does operate in each region to generate irregularities that move in opposite directions under the action of oppositely directed zonal electric fields and favorable plasma density gradients. (2) The type 1 echoes show no structure across their Doppler band and all they come from the same localized region. The localized regions of type 1 echoes in Fig. 6 have mean zonal scales of less than 8 km and traverse across the beam to the west with speeds near 120 m/s.
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Structural stability of the high-aluminium zinc alloys modified with Ti addition

Structural stability of the high-aluminium zinc alloys modified with Ti addition

The initial microstructure of the binary ZnAl26 alloy poured into a sand mould is shown in Fig. 2(a). Fig 2(b) shows the microstructure obtained in the same conditions, but after addition of the 0.04 wt.% Ti, introduced into the melt with the Zn-4wt%Ti master alloy (ZnTi4 MA). Furthermore, Fig. 2(b )clearly shows significant refinement of the dendritic structure of the α(Al) solid solution, which should positively influence plastic properties of the inoculated alloy. On basis of the previous publications [13-15] the observed refinement appears due to heterogeneous nucleation of the α' solid solution on the (Al,Zn) 3 Ti nucleants, originated
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Exploring atmospheric blocking with GPS radio occultation     observations

Exploring atmospheric blocking with GPS radio occultation observations

Steiner, A. K., Hunt, D., Ho, S.-P., Kirchengast, G., Mannucci, A. J., Scherllin-Pirscher, B., Gleis- ner, H., von Engeln, A., Schmidt, T., Ao, C., Leroy, S. S., Kursinski, E. R., Foelsche, U., Gor- bunov, M., Heise, S., Kuo, Y.-H., Lauritsen, K. B., Marquardt, C., Rocken, C., Schreiner, W., Sokolovskiy, S., Syndergaard, S., and Wickert, J.: Quantification of structural uncertainty

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Calculating the uncertainty associated to the forecast of species dispersals: Stochastic Flow Connectivity

Calculating the uncertainty associated to the forecast of species dispersals: Stochastic Flow Connectivity

Flow connectivity (FC hereafter) is a methodology first introduced in 2013 (Ferrarini, 2013) to forecast biotic flows over real landscapes, alternative to circuit theory (McRae, 2006; McRae and Beier, 2007; McRae et al., 2008) and least-cost modelling (Dijkstra, 1959). Its name is due to the fact that it resembles in some way the motion characteristic of fluids over a surface. In fact, FC predicts species dispersal by minimizing at each time step the potential energy due to fictional gravity force over a frictional 3D landscape built upon the real landscape. FC considers connectivity to be a function of a continuous gradient of permeability values rather
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<i>Letter to the Editor</i><br>Abel transform inversion of radio occultation measurements made with a receiver inside the Earth’s atmosphere

<i>Letter to the Editor</i><br>Abel transform inversion of radio occultation measurements made with a receiver inside the Earth’s atmosphere

indicate that ǫ, the angle between positive and negative rays at the receiver, is around 7 degrees for paths that graze the surface. This translates to a horizontal separation between the paths of ∼800 km, when at an altitude of 400 km above the Earth’s surface. In addition, typical ray bending for a path near the surface of around 1.2 ◦ will increase the separation from 800 km to around 950 km. This appears quite large but it needs to be put in some context. Firstly, Hajj and Romans (1998) obtained reasonable ionospheric profile results with an Abel transform of L1 bending angles assuming spheri- cal symmetry. The geometry of their measurements implies that spherical symmetry is effectively being assumed over much greater angles. In addition, it is important to recognise the significance of ionospheric bending compared to neutral bending for a path near the surface. The total bending angle will be of order 1 degree, but the ionospheric contribution will only be of order ∼0.01 ◦ given daytime, solar maximum conditions (Fig. 3, Kursinski et al., 1997). It seems reason- able to expect that the error will be smaller than the iono- spheric signal, so we would anticipate errors of less than 1%. To conclude, we have outlined an inversion method based on an Abel transform that can be applied to RO measure- ments made with a receiver inside the atmosphere. Although further work is required to assess the importance of the as- sumption of spherical symmetry in both neutral atmosphere and ionosphere, we nevertheless believe this may be an inter- esting area for future experimental work.
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Assessment of COSMIC radio occultation retrieval product using global radiosonde data

Assessment of COSMIC radio occultation retrieval product using global radiosonde data

for 4 months. Kishore et al. (2009) validated the first year of COSMIC temperature profiles using radiosonde data and operational stratospheric analysis data. These studies indi- cated that the results of COSMIC show a good agreement with radiosonde, especially the temperature data (see in Ta- ble 1). However, the collocation mismatch criteria were not strict due to the short data periods in those studies, or the comparisons were performed over restricted regions. Sun et al. (2010) reported that, in the troposphere (850–200 hPa), the collocation mismatch impacts on the comparison stan- dard deviation errors for temperature are 0.35 K/3 h and 0.42 K/100 km, and for relative humidity are 3.3 %/3 h and 3.1 %/100 km. In the present study, the assessment used data of 4 yr from 2007 to 2010. A longer period was used to col- lect sufficient samples to reduce the collocation mismatch. This comparison used the 1DVAR retrieval atmospheric oc- cultation profiles wetPrf. The 1DVAR process separated the pressure, temperature and moisture contributions to refrac- tivity, and the wetPrf data is atmospheric occultation profiles with moisture information included. The background used for the 1DVAR process is the ECMWF analysis data.
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The application of optical measurements for the determination of accuracy of gear wheels casts manufactured in the RT/RP process

The application of optical measurements for the determination of accuracy of gear wheels casts manufactured in the RT/RP process

Before taking the measurements, an anti-reflection coating was applied on the tested gear wheel. The thickness of the coating ranged from 0,8 µm do 1,2 µm. The measurements were taken at the Institute of Metrology and Measuring Systems, at Pozna ń University of Technology.

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