Echo Height Research Articles

RADAR Echo Recognition of Squall Line Based on Deep Learning

Squall line (SL) is a convective weather process that often causes disasters. The automatic recognition and early warning of SL are important objectives in the field of meteorology. By collecting the new-generation weather RADARs (CINRAD/SA and CINRAD/SAD) base data during 12 SL weather events occurred in Jiangsu, Shanghai, Shandong, Hebei, and other regions of China from 2019 to 2021, the dataset has a total of 49,920 samples with a window size of 40 km. The 40 km area was labeled by employing manual classification and data augmentation to construct the deep learning dataset with a positive and negative sample ratio of 1:1, of which 80% and 20% are separated as the training and test set, respectively. Based on the echo height of each elevation beam at different distances, three deep learning-based models are trained for SL automatic recognition, which include a near-distance model (M1) trained by the data in nine RADAR elevation angles within 45 km from RADARs, a mid-distance model (M2) by the data in six elevations from 45 to 135 km, and a far-distance model (M3) by the data in three elevations from 135 to 230 km. A confusion matrix and its derived metrics including receiver operating characteristic (ROC) curves and the area under the ROC curve (AUC) are introduced as the indicators to evaluate the models by the test dataset. The results indicate that the accuracy of models are over 86% with the hit rates over 87%, the false alarm rates less than 21%, and the critical success indexes (CSI) surpass 78%. All the optimal critical points on the ROC curves are close to (0, 1), and the AUC values are above 0.95, so the three models have high hit rates and low false alarm rates for ensuring SL discrimination. Finally, the effectiveness of the models is further demonstrated through two SL events detected with Nanjing, Yancheng and Qingpu RADARs.

The Macro- and Microphysical Response Characteristics of the Multicell Hailstorm Hail-Suppression Operation: Case Study

Abstract This study analyzed the macro- and microphysical response characteristics of a typical multicell hailstorm after seeding on 27 April 2019 in Weining, China, using X-band dual-polarization radar (YLD1-D) data. An improved X-pol hydrometeor identification algorithm was employed for hydrometeor identification. According to the diffusion of the seeding agents, the seeded hailstorm was graded into three study regions, and the evolution of the seeded hailstorm was divided into four periods. The response characteristics of the seeded hailstorm in each region and period were compared and analyzed. The results show that 1) macroscopically, the decrease in the reflectivity and the height of strong echo mainly occurred in the seeded period, whereas the decrease in the echo top and the height of the storm was mainly in the postseeded period; the echo height variation of the unseeded hailstorm is obviously different from that of the seeded hailstorm; and 2) from the microscopic perspective, the decrease in low-density graupel and supercooled water and the increase in ice crystals and aggregates in the seeded region mainly occurred in the seeded period, which was consistent with the time required for the “benefit competition” after the silver iodide completed nucleation. When compared with the seeded region, the hydrometeors in the unseeded region had an opposite trend (or an in-phase trend with an obviously lower changing rate), which further indicated the impact of the artificial ice nuclei on microphysical processes in the seeded region. For hailstorms with a high content of supercooled droplets and graupel, the key mechanisms of hail suppression are “cloud water glaciation,” “beneficial competition,” and “early rainout.”

Assessment of understory vegetation in a plantation forest of the southeastern United States using terrestrial laser scanning

Forests of the southeastern United States are home to large timber industries with substantial contributions to global round wood production and paper products. Despite the success of plantations and the large timber industries in this area, pine growth remains constrained due to the competition between planted pine and the species in the understory. Moreover, effective control of this interspecies competition had shown a significant two- to four-times increase in stand productivity. Thus, this study aims to evaluate the use of laser scanning derived data from Terrestrial Laser Scanner (TLS) to assess understory vegetation biomass, as conventional methods utilizing optical imagery have yet to be effective in quantifying and mapping evergreen understory in the southeastern coastal forests of the United States. For this study, we utilized TLS to scan the entire forest profile within 60 sample plots of an operational loblolly pine plantation in Nassau County, Florida, and collected understory biomass data through destructive sampling. We compared three TLS-based volume estimation methods for predicting understory biomass and applied the Adaptive Least Absolute Shrinkage and Selection Operator (ALASSO) regression method to derive an optimal model by integrating the most efficient volume estimation methods and other TLS-derived standard metrics. Our study identifies the 20th percentile of the echo height and a 3D volume metric based on mean height and understory cover as the most significant explanatory variables for the optimal model. The model exhibits high accuracy, with Adjusted R-squared (Adj. R2) of 0.80 and Root Mean Square Error (RMSE) of 234.8 g per square meter (g/m2). Additionally, the mean height and understory-based volume estimation method outperformed other methods, such as voxel count and three dimensional (3D) alpha hall-based method, with Adj. R2 of 0.79, 0.47, and 0.57, and RMSE values of 288, 448.6, and 413 g/m2, respectively, when used as a single variable in the model. The resulting model successfully predicted and quantified understory vegetation, showcasing TLS's potential to accurately capture biomass variation, particularly in evergreen-dominated pine plantation forests in the southeastern United States coastal regions. As a tool for monitoring understory, TLS can be used to aid plantation forest managers in identifying areas that require control measures for enhanced management practices.

An expeditious low-cost method for the acoustic characterization of seabeds in a Mediterranean coastal protected area

Posidonia oceanica meadows are ecosystem engineers which, despite their ecological relevance, are experiencing habitat fragmentation and area decrease. Cartography and information on the ecological status of these habitats is key to an effective maritime spatial planning and management for habitat conservation. In this work we apply an acoustic methodology to map benthic habitats (substrate and vegetation) in an archipelago of the Natura 2000 Network close to the coast of Murcia (SE Spain) where dense and sparse areas of P. oceanica, and patches of Cymodocea nodosa appear over a sandy and had bottom. The methodology uses dual frequency information (200 kHz and 38 kHz) acquired with a single-beam echosounder to develop a bathymetry, and performs sea bottom and vegetation supervised classifications, using video and scuba diver observations as groundtruthing data. Sea bottom was classified from acoustic features of the first and second 200 kHz echoes into 5 substrate classes using a random forest classifier: sand, fine sand, coarse sand, hard bottoms and hard bottoms with sandy patches. The vegetation was classified from features extracted from the "above-bottom" part of the echo (height and backscattering intensity) in both frequencies, resulting also in a 5 class classification: C. nodosa meadows, dense P. oceanica meadows, dispersed P. oceanica meadows, dense P. oceanica with sand patches, and no-vegetation; according to the random-forest Gini index, 38 kHz features were the most informational variables for this classification. The validation accuracies of both classifications were 85% (substrates) and 70% (vegetation), close to accuracies reported in the literature when using a similar number of classes. The results of this article (including bathymetric, and substrate and vegetation thematic maps), together with the acoustic methodology described and used, are contributions that can improve the continuous monitoring of Mediterranean seagrasses.

Observations of the October Draconid outburst at different latitudes along 120°E

ABSTRACT The observations of short-duration meteor showers at different geographic locations are important for well understanding of their outbursts. Using the four all-sky interferometric meteor radars at Mohe (53.49°N, 122.34°E), Beijing (40.3°N, 116.19°E), Wuhan (30.54°N, 114.34°E), and Ledong (18.44°N, 108.97°E) in China, four outbursts (2011, 2012, 2018, and 2019) of the October Draconid meteor shower were observed between 2011 and 2021. The October Draconid meteor velocity was concentrated around 22∼23 km s−1, with an active duration of 6∼9 h and a main peak around the solar longitude 194.73°∼195.63°. When comparing the hourly rates of the October Draconid meteor shower for different years at Mohe, a maximum (minimum) of peak flux was observed in 2012 (2011). The radiants and orbit parameters of the October Draconid meteors derived from the radars at different latitudes are consistent, except that the weighted mean echo height during the peak activity at Mohe was always lower than that at other stations.

MirrorSAR: An HRWS Add-On for Single-Pass Multi-Baseline SAR Interferometry

This article reports the Phase A study results of the interferometric extension of the high-resolution wide-swath (HRWS) mission with three MirrorSAR satellites. According to the MirrorSAR concept, small, low-cost, transponder-like receive-only satellites without radar signal demodulation, digitization, memory storage, downlink, and synchronization are added to the planned German X-band HRWS mission. The MirrorSAR satellites fly a triple helix orbit in close formation around the HRWS orbit and span multiple single-pass interferometric baselines. A comprehensive system engineering and performance analysis is provided that includes orbit formation, MirrorLink, Doppler steering, antenna pattern and swath design, multi-static echo window timing, SAR performance, height performance, and coverage analysis. The overall interferometric system design analysis of Phase A is presented. The predicted performance of the global digital elevation model (DEM) is improved by one order of magnitude compared to presently available global DEM products such as the TanDEM-X DEM.

Radar-Based Assessment of the Detectability of Giant Hail


 The occurrence of giant hail, defined as hail ≥102 mm (4.00 in) in diameter, is a relatively rare phenomenon, accounting for less than 1% of all hail reports in the United States. Despite the infrequent nature of these events, hail of this magnitude has the potential to cause extreme damage to property and a substantial threat to exposed life. The short-term prediction of these events has been challenging. For giant hail since 2005, only 7% of convective warnings and severe-weather statements issued by the National Weather Service (NWS) accurately predicted a maximum hail size ≥102 mm prior to the report, with an average underestimated size error of 55.6 mm (2.19 in).
 The objectives of this study are to determine the detectability of giant hail in convective storms and to improve advanced recognition of these events during NWS warning operations. A total of 568 giant-hail reports, gathered over a 15-y period from 1 January 1995 through 31 December 2009 throughout the contiguous United States, served as the primary database for the research. Weather Surveillance Radar-1988 Doppler (WSR-88D) data and North American Regional Reanalysis (NARR) environmental data were collected for each case. Several radar signatures were examined to assess their utility in discriminating storms most favorable for giant hail. It was found that 99% of the storms were supercells with well-organized structure. Giant-hail producing storms were characterized by median values of rotational velocities of 24 m s-1 (47 kt), storm-top divergence magnitudes of 72 m s-1 (140 kt), and 50-dBZ and 60-dBZ echo heights of 13 100 m (43 000 ft) and 10 600 m (34 800 ft) respectively. Vertically integrated liquid water (VIL)-based products, maximum reflectivity within the storm, and reflectivity within the preferred hail-growth zone showed little to no skill in discriminating between giant hail and smaller hail sizes.

Determining maximum entropy in 3D remote sensing height distributions and using it to improve aboveground biomass modelling via stratification

McArthur's foliage height diversity (FHD) has been the gold standard in the determination of structural complexity of forests characterized by LiDAR vertical height profiles. It is based on Shannon's entropy index, which was originally designed to describe evenness in abundances among qualitative typologies, and thus the calculation of FHD involves subjective layering steps which are essentially unnatural to describe a continuous variable (X) such as height. In this contribution we aim to provide a mathematical framework for determining maximum entropy in 3D remote sensing datasets based on the Gini Coefficient of theoretical continuous distributions, intended to replace FHD as entropy measure in vertical profiles of LiDAR heights (1D, X), with extensions to variables expressing dimensions of higher order (2D or 3D, Z ∝ X2 or X3). Then we apply this framework to Boreal forests in Finland to describe landscape heterogeneity with the intention to improve the modelling of forest aboveground biomass (AGB), hypothesizing that LiDAR models of AGB should essentially be different in areas of differing structural characteristics. We carried out a pre-stratification of LiDAR data collected in 2012 using simple rules applied to the L-skewness (Lskew) and L-coefficient of variation of LiDAR echo heights (Lcv; equivalent to the Gini coefficient, GCH), determining a new threshold at GCH = 0.33 as a consequence of the newly developed mathematical proofs. We observed only moderate improvements in terms of model accuracies: RMSDs reduced from 41.7% to 38.9 or 37.0%. More remarkably, we identified critical differences in the metrics selected at each stratum, which is useful to understand what predictor variables are more important for estimating AGB at each area of a forest. We observed that higher LiDAR height percentiles are more relevant at open canopies and heterogeneous forests, whereas closed canopies in homogeneous forests obtain most accurate predictions from a combination of cover metrics and percentiles around the median. Without stratification, the overall model would neglect explained variability in the structural types of lower occurrence, and predictions from a model influenced by structural types of higher occurrence would be biased at those areas. These results are thus useful in terms of improving our understanding on the relationships underlying LiDAR-AGB models.

An Analysis of the Performance of the Houston Lightning Mapping Array During an Intense Period of Convection During Tropical Storm Harvey

AbstractExtreme lightning activity (∼300,000 flashes) was observed by the Houston Lightning Mapping Array (HLMA) network during Tropical Storm Harvey on August 26, 2017–August 27, 2017. There was an overall weak correlation between the lightning flash and precipitation rates (R = 0.14; p ∼ 0.17) likely due to feeder bands transitioning between deep and shallow convection. The peak precipitation rate (14.2 mm hr−1) lagged the peak lightning flash rate (∼18,000 flashes [30 min]−1) by 7 h. Adjusting for the lag, the correlation increased to 0.71 (p < 0.01) indicating a relationship between the uptick in lightning activity in the convective feeder bands and the resulting heavy precipitation during episodes of shallow convection. Peak lightning flash extent densities of 12.4 km−2 min−1 were spatially collocated with precipitation rates exceeding 9 mm hr−1. NEXRAD reflectivity data featured 30 dBZ echo heights in excess of 10 km that were collocated with peak lightning flash extent densities exceeding 3 km−2 min−1. The NEXRAD specific phase (kdp) and differential phase (Zdr) dual‐polarization products were highest (≥2° km−1 and dB) below the melting layer (4.6 km) indicating heavy precipitation and strong updrafts. Negative kdp and Zdr values (≤−0.15° km−1 and dB) collocated with the peak lightning flash extent density altitudes indicated ice particle generation which likely augmented the charge separation process. This is likely the first time a major tropical cyclone has occurred within the confines of a lightning mapping array. The lightning data, when used synergistically with radar and precipitation data, can adequately quantify tropical convection exhibiting an elevated mixed‐phase depth.

Some features of the day-to-day MLT wind variability in winter 2017–2018 as seen with a European/Siberian meteor radar network

We present results of wind measurements near the mesopause carried out with meteor radars (MRs) at Collm (51°N, 13°E), Obninsk (55°N, 37°E), Kazan (56°N, 49°E), Angarsk (52°N, 104°E) and Anadyr (65°N, 178°E) from October 1, 2017 till March 31, 2018. The Collm and Kazan MRs are SKiYMET radars with vertical transmission and radio echo height finding, while the other radars operate with horizontal transmission and without height finding. We paid particular attention to the meridional wind variability with periods of 4–6 days and 9–11 days. The waves with these periods are seen as spots of the wave activity in the wavelet spectra and include oscillations with different periods and different discrete zonal wavenumbers. These wave packets successively propagate as a group of waves from one site to another one in such a way that they are observed at one site and almost disappear at the previous one. The 4–6 wave group includes planetary-scale oscillations (individual spectral components) which have eastward phase velocities and mostly zonal wavenumbers 2 and 3, and the vertical wavelength exceeds 70 km at middle latitudes. The source of the oscillations is the polar jet instability. The wave group itself propagates westward, and the amplitudes of wind oscillations are approximately 5–6 m/s as obtained from the wind data averaged over the meteor zone. The 9–11 day wave set propagates westward as a group and mainly consists of spectral components which have westward phase velocity and zonal wavenumber 1. Amplitudes of these wind perturbations strongly vary from station to station and can reach, approximately, 8 m/s. The vertical wavenumber is 0.014 km−1 as taken from the Kazan and 0.05 km−1 according to the Collm data. We obtained a global view on the waves by using the AURA MLS geopotential data. We found a good correspondence between wave features obtained from the MR wind measurements and the MLS data. To our knowledge, such a wave propagation of planetary wave in the mesosphere/lower thermosphere (MLT) region has so far not obtained much attention.

Ultrasound diagnosis and differential diagnosis of medium and small choroidal melanomas

Objective: To analyze the ultrasound diagnosis and differential diagnosis of medium and small choroidal melanomas. Methods: It was a retrospective case series study. Thirty-six cases (36 eyes) with medium or small choroidal melanoma were collected between January 2016 and January 2017 in Beijing Tongren Hospital, including 16 males and 20 females aged (50±12) years old. All tumors' apical heights were within 5 mm and the largest basal diameter was within 15 mm. Sixty-nine cases (69 eyes) with choroidal hemangioma, including 45 males and 24 females aged (45±11) years old, and 16 cases (19 eyes) with choroidal metastasis, including 4 males and 12 females aged (50±11) years old, of equal size were also analyzed as differential diagnosis. Univariate (Chi-square test, Fisher's exact test, and analysis of variance) and multivariate analyses (Logistic regression) were used for statistical analysis. Results: There were significant differences in morphology, height, base-height ratio, internal echo, choroidal excavation and secondary retinal detachment among the three types of tumors(all P<0.05). Approximately 91.7% (33/36) of choroidal melanomas and 94.2% (65/69) of hemangiomas were flat or dome, while 63.2% (12/19) of metastatic tumors showed a polygonal shape and an irregular surface contour. The average height was (4.02±0.70) mm for choroidal melanoma, (3.10±1.08) mm for metastasis and (2.75±0.87) mm for hemangioma. The base-height ratio of choroidal melanoma, metastasis, and hemangioma was 2.62±0.48, 4.09±1.18 and 3.16±0.58, respectively. About 86.1% (31/36) of choroidal melanomas and 84.2% (16/19) of metastases showed lower echo than adjacent orbital tissue, while 92.8% (64/69) of hemangiomas had similar or higher echo. About 16.7% (6/36) of choroidal melanomas showed choroidal excavation, but no such signs were found in other tumors. Approximately 80.6% (29/36) of choroidal melanomas, 78.9% (15/19) of metastases and 52.2% (36/69) of hemangiomas showed secondary retinal detachment. The internal echo, height and base-height ratio were taken as significant independent influencing factors into the Logistic regression model. The low internal echo and large height were risk factors of choroidal melanoma (OR=0.016, 0.199, both P<0.05), while the low echo and large base-height ratio were risk factors of choroidal metastasis (OR=0.011, 0.073, both P<0.05). Conclusion: Ultrasonography plays an important role in the diagnosis of medium and small choroidal melanomas, and the echo, height, and base-height ratio of the lesion can be helpful for the diagnosis and differential diagnosis. (Chin J Ophthalmol, 2018, 54: 843-848).

Meteor echo height ceiling effect and mesospheric temperature estimation from meteor radar observations

Abstract. The mesospheric temperature estimation from meteor height distribution is reevaluated by using the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) and the King Sejong Station (KSS) meteor radar observations. It is found that the experimentally determined proportionality constant between the full width at half maximum (FWHM) of the meteor height distribution and temperature is in remarkable agreement with theoretical value derived from the physics-based equation and it is nearly time-invariant for the entire observation period of 2012–2016. Furthermore, for the first time we found that the FWHM provides the best estimate of temperature at slightly lower height than the meteor peak height (MPH) by about 2–3 km. This is related to the asymmetric distribution of meteor echoes around MPH, which is known to be caused by the meteor echo height ceiling effect (MHC). At higher altitude above MPH, the meteor detection rate is greatly reduced due to the MHC, and the cutoff height for this reduction follows a fixed molecular mean free path of the background atmosphere. This result indicates that the meteor height distribution can be used to estimate the mesospheric temperature, even under the asymmetric meteor echo distribution caused by the MHC at high altitude.

Relationships between Extreme Rain Rates and Convective Intensities from the Perspectives of TRMM and WSR-88D Radars

AbstractTRMM PR 2A25, version 7 (V7), retrievals of reflectivity Z and rainfall rate R are compared with WSR-88D dual-polarimetric S-band radar data for 28 radars over the southeastern United States after matching their horizontal resolution and sampling. TRMM Ku-band measurements are converted to S-band approximations to more directly compare reflectivity estimates. Rain rates are approximated from WSR-88D data using the CSU–hydrometeor identification rainfall optimization (HIDRO) algorithm. Tropics-wide TRMM retrievals confirm previous findings of a low overlap fraction between extreme convective intensity, as approximated by the maximum 40-dBZ height, and extreme near-surface rain rates. WSR-88D data also confirm this low overlap but show that it is likely higher than TRMM PR retrievals indicate. For maximum 40-dBZ echo heights that extend above the freezing level, mean WSR-88D reflectivities at low levels are approximately 2 dB higher than TRMM PR reflectivities. Higher WSR-88D-retrieved rain rates for a given low-level reflectivity combine with these higher low-level reflectivities for a given maximum 40-dBZ height to produce rain rates that are approximately double those retrieved by the TRMM PR for maximum 40-dBZ heights that extend above the freezing level. TRMM PR path-integrated attenuation, and WSR-88D specific differential phase, differential reflectivity, and hail fraction indicate that the TRMM PR 2A25 V7 algorithm is possibly misidentifying low–midlevel hail and/or graupel as greater attenuating liquid, or vice versa. This misidentification, coupled with underestimation of path-integrated attenuation caused by nonuniform beamfilling and higher rain rates produced by specific differential phase (KDP)–R than Z–R relationships, results in low-biased 2A25 V7 rain rates in intense convection.

Cloud-Precipitation Parameters and Radiative Forcing of Warm Precipitating Cloud over the Tropical Pacific Ocean Based on TRMM Datasets and Radiative Transfer Model

An approach is proposed for combining observations from the Precipitation Radar (PR) and the Visible and Infrared Scanner (VIRS) onboard the TRMM (Topical Rainfall Measuring Mission) satellite to investigate the climatology of warm precipitating cloud (WPC) microphysical properties, such as cloud effective radius (Re), cloud optical depth (Tau), and liquid water path (LWP) in the tropical Pacific Ocean (20° S–20° N) from 1998 to 2012. The WPCs are captured by VIRS/PR and categorized into two extreme (light and heavy) rain rate types (EL-WPC, EH-WPC). Their radiative effects are also simulated by the Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) radiative transfer model. The results indicate that total, EL-WPC and EH-WPC reach their highest occurrence frequencies of 22%, 1.6% and 2.0% in the North-west Pacific, Intertropical Convergence Zone (ITCZ) and South Pacific Convergence Zone (SPCZ), respectively. Most of the EL-WPC has higher ratio to total WPC in the Pacific warm pool with warmer sea-surface temperature (SST), while the higher ratio for EH-WPC is located in SPCZ associated with deep convection. WPC has an average Re of 15.6 μm, Tau of 20, and LWP of 200 g m−2. EL-WPC is a little larger average Re than EH-WPC, and larger Re is distributed with higher echo top height (H). Moreover, for EH-WPC, the increased Re by the collision-coalescence process in lower H (&lt;3.5 km) generates a stronger rain rate. In addition, although the H of EH-WPC decreases along the increased brightness temperature at 10.8 μm (BT4), this is not obvious in EL-WPC possibly due to a certain echo height to generate a light precipitation. With an increased rain rate of WPC, Re becomes larger in EL-WPC and smaller in EH-WPC. EL-WPC induces a cooling of approximately −0.5 W m−2 for radiative forcing, which is −3.0 W m−2 less than the EH-WPC.

Stratiform and Convective Precipitation Properties of Tropical Cyclones in the Northwest Pacific

AbstractThe properties of stratiform and the convective precipitation of tropical cyclones (TCs) over the northwest Pacific are examined using the Tropical Rainfall Measuring Mission data for 1998–2013. TCs are classified into inner core (IC), inner rainband (IB), and outer rainband (OB) regions, and the results show that TCs are dominated by stratiform precipitation, which accounts for more than 78% of the total raining area. The highest fraction of the stratiform raining area exists in the IB region and increases as the TC intensity increases (from 80% to 93%). Strong convective signatures generally occur in the IC region, less often in the IB region, and least often in the OB region. Stratiform precipitation in the IC region generally has comparable or even stronger ice scattering signatures and higher 20 dBZ radar echo heights than the convective precipitation in the IB and OB regions. Weak convection decreases significantly as the TC intensity increases, which leads to increased convective intensity. Stratiform (convective) precipitation accounts for 61% (39%) of the total TC volumetric rain and 25% (75%) of the total TC lightning flash, respectively. Moreover, stratiform precipitation's contribution to the total TC volumetric rain and lightning flash increases as the TC intensity increases, which indicates that stronger TCs are favorable for maintaining more stratiform precipitation. The stratiform and convective precipitation properties in different TC regions and intensities cooperatively change with the enhanced ascending branch in the IC region and the radial outflow at the upper levels of the secondary circulation.

Variation of the meteor count rate and echo height during solar cycle 23 and 24

AbstractThe meteoroid ablation is an important source of upper atmosphere metal atoms. Many meteoroids ablate between 70 - 110 km and form an ionized plasma trail which is detected by radar technique. It is also known that the ablation heights of the meteors depend on various factors such as velocity, mass, and its composition, etc. The meteor ablation height provides new opportunities to gather information on the neutral atmosphere in the Mesosphere and Lower Thermosphere (MLT) region. In this study, we analysed the 11 years of meteor radar data (2005 - 2015), i.e., descending phase of solar cycle 23, and ascending phase of solar cycle 24, detected by all sky meteor radar at Thumba. We found that the solar activity influences the meteor ablation height, here, during the solar maxima meteor peak detection height rise to few hundred meters higher altitudes. We also examined the long term pattern of the meteor count rate which shows a decreasing trend and has good agreement with the sunspot number (SSN).

Climatological Beam Propagation Conditions for China’s Weather Radar Network

AbstractThe vertical refractivity gradient (VRG) is critical to weather radar beam propagation. The most common method of calculating beam paths uses the 4/3 Earth radius model, which corresponds to standard refraction conditions. In the present work, to better document propagation conditions for radar electromagnetic waves, which is essential for hydrology and numerical weather forecast models to more fully benefit from observations taken from the new-generation weather radar network in China, VRG spatial and temporal variations in the first kilometers above the surface are explored using 6-yr sounding observations. Under the effects of both regional climatic and topographic conditions, VRG values for most of the radars are generally smaller than those of the standard conditions for much of the year. There are similar or slightly larger values at only a few radar sites. Smaller VRG values are more frequent and widespread, especially during rainy seasons when weather radar observations are important. In such conditions, beam heights estimated using standard atmospheric refraction are overestimated relative to actual heights for most of the radars. Underestimates are much less common and of much shorter duration. However, height deviations are acceptable for being well within the uncertainty of radar echo height owing to the ~1° beamwidth. In coastal areas and the middle and lower reaches of the Yangtze River, radar observations should be applied with much more caution because of the greater risk of beam blockage and clutter contamination.

Evaluating Transport Properties of LiPF6 in Concentrated EC/DEC Electrolytes By Self-Diffusivity from NMR

Accurate prediction of the lithium ion battery charge-discharge behavior is critically important in many battery applications1, including for the high-power, high-energy battery packs used in electric vehicles. Accurate model predictions by, for instance, the classical porous electrode model developed by John Newman2, require accurate electrolyte solution transport properties. In this work, the self-diffusivities of all species in LiPF6/EC/DEC electrolyte solutions were characterized by PFG-NMR, and the protocol reported by Kim and Srinivasan3was used to evaluate the transport properties. Experimental All chemicals were purchased from BASF. LiPF6 in EC/DEC (w/w 50:50) of different concentrations (1.5M to 0.1M) were prepared inside an argon-filled glove box and sealed in aluminum bottles before the PFG-NMR measurement.5 Diffusion coefficients (D) of the Li+, PF6 - , and EC/DEC were measured by 7Li 19F and 1H PFG stimulated echo NMR spectroscopy. Since resonances from EC, DEC are separated in one-dimensional 1H spectra, separate diffusion coefficients could be measured. Experiments were performed at Larmor frequencies of 599.82 and 564.3 MHz for 1H and 19F, respectively, over the temperature range of 0 to 40 oC using a 14.1 T (600 MHz 1H) NMR spectrometer (Agilent) equipped with a 5 mm z-gradient probe (Doty Scientific), which can generate a maximum gradient strength of approximately 31 T/m. The echo heights, S(g), recorded as a function of gradient strength, g, were fitted with the Stejskal-Tanner equation (equation 1), RESULTS AND DISCUSSIONShown in Figure 1 is the concentration dependence of self-diffusivity of LIPF6/EC/DEC measured by PFG-NMR for Li+, PF6 -, EC and DEC. Careful inspection of the data leads to several conclusions below: I. the self-diffusivities of all species decrease as the concentration increases or the temperature decreases, which is expected from the Stokes-Einstein equation II. the self-diffusivity values are ordered as follows EC≈DEC>PF6 ->Li+ III. the concentration dependence of self-diffusivity for PF6 -is stronger than other species, especially at lower concentrations, e.g. 0.1 M to 1.0 M, while Li+ shows the weakest dependence. The generalized-Darken relation (Equation 1) for translating self-diffusivities and of species i and j into binary diffusivities, Dij, is given by equation (2): where xi , xj , are component mole fractions. This relation was validated by Krishna and van Baten4. The resulting Fickian diffusivity values decrease as the concentration increases in a narrow range (3.7x10-10 to 2.4x10-10m2/s), and have similar magnitudes to these reported in EC/DEC or PC/EC/DMC as measured by electrochemical methods over a wide range of concentrations. Lundgren et al. 6 reported that the Fickian diffusivities of LiPF6 in the same electrolyte decreased from 2.8x10-10m2/s to 2.0x10-10 m2/s in the range of 0.5M to 1.5M, as measured by galvanostatic polarization experiments (red connected points, Figure 2); Valøen and Reimers 7 measured the Fickian diffusion coefficients of LiPF6in a PC/EC/DMC mixture (10:27:63) (blue connected points, Figure 2). Reference 1. L. Cai, R. E. White J. Power Sources14 (2011): 5985. 2. J. Newman, W. Tiedemann, Aiche Journal21 (1975), 25. 3. S. Kim, V. Srinivasan, J. Electrochem. Soc. 163(2016), A2977. 4. R. Krishna, J. M. van Baten, Ind. Eng. Chem. Res., 44(2005), 6939. 5. K. Han, N. Rajput, X. Wei, W. Wang, J. Hu, K. Persson, K. Mueller J. Chem. Phys., 141(2014), 104509. 6. H. Lundgren, M. Behm, G. Lindbergh, J. Electrochem. Soc., 162(2015), A413. 7. Lars Ole Valøena, and J. Reimersa, J. Electrochem. Soc., 152 (2005), A882. Figure 1

Modeling Mediterranean forest structure using airborne laser scanning data

The conservation of biological diversity is recognized as a fundamental component of sustainable development, and forests contribute greatly to its preservation. Structural complexity increases the potential biological diversity of a forest by creating multiple niches that can host a wide variety of species. To facilitate greater understanding of the contributions of forest structure to forest biological diversity, we modeled relationships between 14 forest structure variables and airborne laser scanning (ALS) data for two Italian study areas representing two common Mediterranean forests, conifer plantations and coppice oaks subjected to irregular intervals of unplanned and non-standard silvicultural interventions. The objectives were twofold: (i) to compare model prediction accuracies when using two types of ALS metrics, echo-based metrics and canopy height model (CHM)-based metrics, and (ii) to construct inferences in the form of confidence intervals for large area structural complexity parameters.Our results showed that the effects of the two study areas on accuracies were greater than the effects of the two types of ALS metrics. In particular, accuracies were less for the more complex study area in terms of species composition and forest structure. However, accuracies achieved using the echo-based metrics were only slightly greater than when using the CHM-based metrics, thus demonstrating that both options yield reliable and comparable results. Accuracies were greatest for dominant height (Hd) (R2=0.91; RMSE%=8.2%) and mean height weighted by basal area (R2=0.83; RMSE%=10.5%) when using the echo-based metrics, 99th percentile of the echo height distribution and interquantile distance. For the forested area, the generalized regression (GREG) estimate of mean Hd was similar to the simple random sampling (SRS) estimate, 15.5m for GREG and 16.2m SRS. Further, the GREG estimator with standard error of 0.10m was considerable more precise than the SRS estimator with standard error of 0.69m.

Cross Spectral Analysis of CODAR-SeaSonde Echoes from Sea Surface and Ionosphere at Taiwan

It is well known that the primary targets responsible for first-order sea echoes observed by a High-Frequency (HF) radar are the advancing and receding ocean waves with the wavelengths at Bragg scales. However, in light of the fact that the ionospheric sporadic E (Es) and F layers may be present in the viewing range of the HF radar for ocean wave detection, the radar returns reflected from the F and Es layers may significantly contaminate the ocean wave power spectrum. The characteristics of the first-order sea echoes and ionospheric interferences measured by the CODAR-SeaSonde in Taiwan area are analyzed and presented in this article. The coherences and phases of the normalized cross spectra of the sea and ionospheric echoes between different pairs of the receiving channels are calculated, respectively. One of the striking features presented in this report is that the ionospheric echo heights scaled from the ionogram observed by the Chung-Li ionosonde are about 30 km lower than those observed by the DATAN CODAR-SeaSonde. It is also found that the coherences of the sea echoes are generally smaller than those of the ionospheric echoes by about 15% on average, and the phase fluctuations (standard deviations) of the sea echoes are substantially larger than those of the ionospheric layer reflection echoes. In addition, statistics show that the sum of the mean phases of the ionospheric echoes between the three receiving channel pairs is approximately zero, while it is not for the sea echoes. These results seem to suggest that the use of the discrepancies in the characteristics of the coherences and phases between the sea and ionospheric echoes may provide a potential means to be helpful to distinguish the sea and ionospheric echoes in the CODAR-SeaSonde observed cross power spectrum.