Characterization of dynamic evolution of the spatio-temporal variation of rain-field in Hong Kong

A significant part of Hong Kong has hilly terrain with relatively short flow concentration time and, hence, is susceptible to the threat of flash floods and landslides during intense convective thunderstorms and tropical cyclones. For places like Hong Kong, a rainfall model that could adequately capture small-scale temporal and spatial variations would be highly desirable. The main challenge in rain-field modeling is to capture and describe the dynamic time-space evolution of the rainfall during rainstorm events. In this study, radar data with a high spatial (1 km2) and temporal (6 min) resolution of four rainstorm events in Hong Kong are analyzed. A geostatistical approach based on indicator variograms of rain-fields is used. The spatial structure of a rain-field is found to be highly anisotropic and should be adequately considered in the model. Variability of the spatial structure of a rain-field was described well by the main features of the variograms. Moreover, it is possible to identify whether multiple rainstorm centers exist by comparing the mean length and range. In order to establish reliable statistics on the spatial and temporal structure of rain-fields in Hong Kong, this approach could be applied to a large set of rainstorm events in this same region in the future.

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Kalmag: a high spatio temporal model of the Geomagnetic field

10.5194/egusphere-egu21-7173 ◽

2021 ◽

Author(s):

Julien Baerenzung ◽

Matthias Holschneider

Keyword(s):

Geomagnetic Field ◽

Learning Algorithm ◽

Dynamical Evolution ◽

Small Scale ◽

Large Set ◽

The Core ◽

Resolution Model ◽

Auto Regressive ◽

Spatio Temporal ◽

Marine Vessels

We present a new high resolution model of the Geomagnetic field spanning the last 121 years. The model derives from a large set of data taken by low orbiting satellites, ground based observatories, marine vessels, airplane and during land surveys. It is obtained by combining a Kalman filter to a smoothing algorithm. Seven different magnetic sources are taken into account. Three of them are of internal origin. These are the core, the lithospheric &#160;and the induced / residual ionospheric fields. The other four sources are of external origin. They are composed by a close, a remote and a fluctuating magnetospheric fields as well as a source associated with field aligned currents. The dynamical evolution of each source is prescribed by an auto regressive process of either first or second order, except for the lithospheric field which is assumed to be static. The parameters of the processes were estimated through a machine learning algorithm with a sample of data taken by the low orbiting satellites of the CHAMP and Swarm missions. In this presentation we will mostly focus on the rapid variations of the core field, and the small scale lithospheric field.&#160; We will also discuss the nature of model uncertainties and the limitiations they imply.

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New methods for retrieval of chlorophyll red fluorescence from hyper-spectral satellite instruments: simulations and application to GOME-2 and SCIAMACHY

10.5194/amt-2015-387 ◽

2016 ◽

Cited By ~ 7

Author(s):

J. Joiner ◽

Y. Yoshida ◽

L. Guanter ◽

E. M. Middleton

Keyword(s):

Spatial Scales ◽

Temporal Structure ◽

Emission Feature ◽

Ozone Monitoring Instrument ◽

Additional Information ◽

Time Space ◽

Hyper Spectral ◽

Spatio Temporal ◽

Gas Measurements ◽

Satellite Instruments

Abstract. Global satellite measurements of solar-induced ﬂuorescence (SIF) from chlorophyll over land and ocean have proven useful for a number of different applications related to physiology, phenology, and productivity of plants and phytoplankton. Terrestrial chlorophyll ﬂuorescence is emitted throughout the red and far-red spectrum, producing two broad peaks near 683 and 736 nm. From ocean surfaces, phytoplankton ﬂuorescence emissions are entirely from the red region. Studies using satellite-derived SIF over land have focused almost exclusively on measurements in the far- red, since those are the most easily obtained with existing instrumentation. Here, we examine new ways to use existing hyper-spectral satellite data sets to retrieve red SIF over both land and ocean. Our approach offers noise reductions as compared with previously published solar line ﬁlling retrievals by making use of the oxygen (O2) γ-band that is not affected by SIF. The O2 γ-band in conjunction with solar Fraunhofer lines help to anchor the O2 B-band that provides additional information on red SIF. Biases due to instrumental artifacts that vary in time, space, and with instrument, must be addressed in order to obtain reasonable results. The satellite instruments that we use were designed to make atmospheric trace- gas measurements and are therefore not optimal for observing SIF; they have coarse spatial resolution and only moderate spectral resolution (∼0.5 nm). Nevertheless, these instruments offer a unique opportunity to compare red and far-red terrestrial SIF at regional spatial scales. Our eight year record of red SIF observations over land with the Global Ozone Monitoring Instrument 2 (GOME-2) allows for the ﬁrst time reliable global mapping of monthly anomalies. These anomalies are shown to have similar spatio-temporal structure as those in the far-red, particularly for drought-prone regions. There is a somewhat larger percentage response in the red as compared with the far-red for these areas that are sensitive to soil moisture, although the differences are within the speciﬁed uncertainties that are dominated by systematic errors. We also demonstrate that high quality ocean ﬂuorescence line height retrievals can be achieved with GOME-2 and similar instruments by utilizing the full complement of radiance measurements that span the red SIF emission feature.

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Spatio-temporal structure of Alfvén waves excited by a sudden impulse localized on an L-shell

Annales Geophysicae ◽

10.5194/angeo-30-1099-2012 ◽

2012 ◽

Vol 30 (7) ◽

pp. 1099-1106 ◽

Cited By ~ 9

Author(s):

D. Yu. Klimushkin ◽

P. N. Mager ◽

K.-H. Glassmeier

Keyword(s):

Resonance Frequency ◽

Temporal Structure ◽

Alfven Wave ◽

Energy Concentration ◽

Small Scale ◽

Source Surface ◽

Local Resonance ◽

Sudden Impulse ◽

Magnetic Shell ◽

Spatio Temporal

Abstract. This paper is concerned with the spatial structure and temporal evolution of the azimuthally small scale Alfvén wave generated by a sudden impulse concentrated on a given magnetic shell. At the outset, both poloidal and toroidal components are present in the wave's magnetic field. The oscillation in the poloidal component on a given magnetic shell is a superposition of two monochromatic oscillations, one with the local resonance frequency on this shell, and the other with the frequency corresponding to the resonance frequency on the source surface. The superposition of these two oscillations leads to beating. Due to phase mixing, the poloidal component of the oscillation decreases with time down to zero, transferring its energy to the toroidal component. Beating in the toroidal component is less pronounced. As time elapses, energy concentration near the source magnetic shell occurs with the frequency of the oscillation corresponding to the Alfvénic resonance frequency on this surface. Outside this thin region wave amplitudes become rather small at oscillation frequencies corresponding to the local resonance frequency of the respective magnetic shell.

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Spatial interpolation of rain-field dynamic time-space evolution based on radar rainfall data

Hydrology Research ◽

10.2166/nh.2020.115 ◽

2020 ◽

Vol 51 (3) ◽

pp. 521-540

Author(s):

Peng Liu ◽

Yeou-Koung Tung

Keyword(s):

Temporal Distribution ◽

Radar Data ◽

Indicator Kriging ◽

Distribution Functions ◽

Cumulative Distribution ◽

Radar Rainfall ◽

Time Space ◽

Geostatistical Approach ◽

Wide Range ◽

Dynamic Time

Abstract Accurate and reliable measurement and prediction of the spatial and temporal distribution of rain field over a wide range of scales are important topics in hydrologic investigations. In this study, a geostatistical approach was adopted. To estimate the rainfall intensity over a study domain with the sample values and the spatial structure from the radar data, the cumulative distribution functions (CDFs) at all unsampled locations were estimated. Indicator kriging (IK) was used to estimate the exceedance probabilities for different preselected threshold levels, and a procedure was implemented for interpolating CDF values between the thresholds that were derived from the IK. Different probability distribution functions of the CDF were tested and their influences on the performance were also investigated. The performance measures and visual comparison between the observed rain field and the IK-based estimation suggested that the proposed method can provide good results of the estimation of indicator variables and is capable of producing a realistic image.

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The spatio-temporal structure of impulse-generated azimuthalsmall-scale Alfvén waves interacting with high-energy chargedparticles in the magnetosphere

Annales Geophysicae ◽

10.5194/angeo-22-1053-2004 ◽

2004 ◽

Vol 22 (3) ◽

pp. 1053-1060 ◽

Cited By ~ 8

Author(s):

D. Yu. Klimushkin ◽

P. N. Mager

Keyword(s):

Growth Rate ◽

Temporal Structure ◽

High Energy ◽

Alfven Waves ◽

Mhd Waves ◽

Alfvén Waves ◽

Small Scale ◽

Ionospheric Conductivity ◽

Spatio Temporal ◽

Field Lines

Abstract. It is assumed to date that the energy source of azimuthal small-scale ULF waves in the magnetosphere (azimuthal wave numbers m≧1) is provided by the energetic particles interacting with the waves through the bounce-drift resonance. In this paper we have solved the problem of the bounce-drift instability influence on the spatio-temporal structure of Alfvén waves excited by a source of the type of sudden impulse in a dipole-like magnetosphere. It is shown that the impulse-generated Alfvén oscillation within a time τ~m∕ΩTN (where ΩTN is the toroidal eigenfrequency) is a poloidal one, and each field line oscillates with its own eigenfrequency that coincides with the poloidal frequency of a given L-shell. As time elapses, the wave becomes toroidally polarized because of the phase difference of the disturbance, and the oscillation frequency of field lines tends to the toroidal frequency. The drift-bounce instability growth rate becomes smaller during the wave temporal evolution, and the instability undergoes stabilization when the wave frequency coincides with the toroidal eigenfrequency. The total amplification of the wave can be estimated as , where is the wave growth rate at the beginning of the process, when it has its maximum value. The wave amplitude can increase only within a time ~τ, when it is poloidally polarized. After this time, when the wave becomes to be toroidally polarized, it goes damped because of the finite ionospheric conductivity. This is in qualitative agreement with the recent radar experimental data.Key words. Magnetospheric physics (MHD waves and instabilities). Space plasma physics (kinetic and MHD theory; wave-particle interactions)

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Sensing Ionospheric Turbulence Using GNSS

10.5194/egusphere-egu2020-8604 ◽

2020 ◽

Author(s):

Giulio Tagliaferro ◽

Andrea Gatti ◽

Eugenio Realini

Keyword(s):

Structure Function ◽

Power Law ◽

Large Scale ◽

Ionospheric Plasma ◽

Temporal Structure ◽

Turbulent Medium ◽

Structure Characteristic ◽

Small Scale ◽

Polar Regions ◽

Spatio Temporal

Electron density in ionospheric plasma exhibits fluctuations and irregularities in time and space, at several scales. Plasma, being ionized gas, is subject to a turbulent behaviour similar to that observed in fluid dynamics, with two main distinctions: a) its dynamics are coupled with electromagnetic fields; b) collisions of particles are rare. These unique properties characterize the inertial range of ionospheric plasma turbulence, which represents the energy cascade from large-scale structures (e.g. travelling ionospheric disturbances) to small-scale ones (eddies) until energy dissipation occurs.&#160;Kolmogorov power law would predict a spectrum of 8/3 and equivalently a structure function with a power law of 5/3 for a phase signal crossing a 3D turbulent medium. However, the previous investigation of spatial structure characteristic of the ionosphere using LOFAR array observed a power law of around 1.9 in the spatial domain. In this study, we investigate the spatio-temporal and temporal structure of the ionosphere using structure function of GNSS phase geometry free signals from both medium earth orbit satellites and geostationary ones. We found two regimes, one compatible the 5/3 Kolmogorov theory and one obeying a 2 power law. We propose an interpretation for the two regimes, the first being a 3D turbulent flow driven by local instabilities, and the second one being driven by solar radiation-induced ionization and successive recombination. The second spectrum obeys a power law of 2, that is the power spectrum of a sinusoidal function like the local sun elevation. By using receivers at almost constant solar irradiance located in polar regions, we further observe the turbulent regimes also in spatio-temporal structure function.

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Small-Scale Rainfall Variability Impacts Analyzed by Fully-Distributed Model Using C-Band and X-Band Radar Data

Water ◽

10.3390/w11061273 ◽

2019 ◽

Vol 11 (6) ◽

pp. 1273 ◽

Cited By ~ 2

Author(s):

Igor Paz ◽

Bernard Willinger ◽

Auguste Gires ◽

Bianca Alves de Souza ◽

Laurent Monier ◽

...

Keyword(s):

Data Quality ◽

Rainfall Variability ◽

Drainage System ◽

Radar Data ◽

Rainfall Data ◽

Distributed Model ◽

Small Scale ◽

Distributed Models ◽

X Band ◽

Spatio Temporal

Recent studies have highlighted the need for high resolution rainfall measurements for better modelling of urban and peri-urban catchment responses. In this work, we used a fully-distributed model called “Multi-Hydro” to study small-scale rainfall variability and its hydrological impacts. The catchment modelled is a semi-urban area located in the southwest region of Paris, an area that has been previously partially validated. At this time, we make some changes to the model, henceforth using its drainage system globally, and we investigate the influence of small-scale rainfall variability by modelling three rainfall events with two different rainfall data inputs: the C-band radar data provided by Météo-France at a 1 km × 1 km × 5 min resolution, and the new X-band radar (recently installed at Ecole des Ponts, France) data at a resolution of 250 m × 250 m × 3.41 min, thereby presenting the gains of better resolution (with the help of Universal Multifractals). Finally, we compare the Multi-Hydro hydrological results with those obtained using an operational semi-distributed model called “Optim Sim” over the same area to revalidate Multi-Hydro modelling, and discuss the model’s limitations and the impacts of data quality and resolution, observing the difficulties associated with semi-distributed models when accounting the spatial variability of weather radar data. This work concludes that it may be useful in future to improve rainfall data acquisition, aiming for better spatio-temporal resolution (now achieved by the weather dual-polarized X-band radars) and data quality when considering small-scale rainfall variability, and to merge deterministic, fully-distributed and stochastic models into a hybrid model which would be capable of taking this small-scale rainfall variability into account.

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Evaluating Plantation Forest vs. Natural Forest Regeneration for Biodiversity Enhancement in Hong Kong

Forests ◽

10.3390/f12050593 ◽

2021 ◽

Vol 12 (5) ◽

pp. 593

Author(s):

Janet E. Nichol ◽

Sawaid Abbas

Keyword(s):

Hong Kong ◽

Species Richness ◽

Forest Regeneration ◽

Forest Succession ◽

Natural Forest ◽

Plantation Forestry ◽

Aerial Photographs ◽

Continuous Increase ◽

Natural Forest Regeneration ◽

Spatio Temporal

Global trends predict a continuous increase in the proportion of forest occupied by plantations up to the end of the 21st century, while a dramatic loss of biodiversity is foreseen as a result of anthropogenic exploitation and climate change. This study compares the role and performance of plantation policies in Hong Kong, with natural regeneration of secondary forest, using detailed spatio-temporal data extracted from a previous study. The study extends over a 70-year period from 1945 to 2014 using aerial photographs and satellite images of five time periods to document spatio-temporal trends in plantation forestry and natural forest succession. Field data on species richness and woody biomass at different stages of forest succession are compared with available data from plantations in the same study area. Results indicate that plantation forests support relatively few native species in the understory, with much lower species richness than naturally regenerated forest, even after 6 to 7 decades. Time-sequential maps of habitat change show that natural forest succession from barren grassy hillsides, progressed at an annual rate of 7.8%, from only 0.2% of the landscape post WWII, to over 37% today. Plantation forestry on the other hand has been less successful, and has even acted as a barrier to natural forest regeneration, as mono-cultural plantations from the late 1960s to 1980s are still plantations today, whereas other similar areas have succeeded naturally to forest. The theory of plantations acting as a nurse crop for a woody native understory is not supported, as Pinus massoniana plantations, destroyed by two deadly nematodes during the 1970s, apparently had no woody understory, as they were seen to have reverted to grassland in 1989 and are still mainly grassland today.

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DEM Based Study on Shielded Astronomical Solar Radiation and Possible Sunshine Duration under Terrain Influences on Mars by Using Spectral Methods

ISPRS International Journal of Geo-Information ◽

10.3390/ijgi10020056 ◽

2021 ◽

Vol 10 (2) ◽

pp. 56

Author(s):

Siwei Lin ◽

Nan Chen

Keyword(s):

Solar Radiation ◽

Spatial Structure ◽

Sunshine Duration ◽

Temporal Structure ◽

Temporal Distribution ◽

Planetary Science ◽

Shielding Effect ◽

Critical Area ◽

Martian Surface ◽

Test Region

Solar radiation may be shielded by the terrain relief before reaching the Martian surface, especially over some rugged terrains. Yet, to date, no comprehensive studies on the spatial structure of shielded astronomical solar radiation (SASR) and the possible sunshine duration (PSD) on Mars have been conducted by previous researchers. Previous studies generally ignored the influences of the terrain on the SASR and PSD, which resulted in a corresponding unexplored field on SASR. The purpose of this paper is to study the Martian spatial-temporal structure of SASR and the PSD under terrain influences. In this paper, the theory of Earth’s SASR, the previous Martian SASR model and the theory of planetary science were combined to propose the SASR model that can be applied to Mars. Then, with the spectrum method theory of geography, we defined two new concepts of spectrums to explore the spatial-temporal distribution of SASR and PSD in different Martian landforms. We found SASR and PSD on Mars were significantly influenced by terrain relief and latitude and showed sufficient regularity, which can be concluded as a gradual attenuation with terrain relief and a regularity of latitude anisotropy. The latitude anisotropy feature is a manifestation of the terrain shielding effect. With the latitude varying, SASR and PSD at different temporal scale generally showed different features with those of Earth, which may be attributed to the imbalanced seasons caused by Martian moving orbits and velocity. Compared to PSD, SASR showed more regular variation under terrain relief and was more influenced by the terrain relief which revealed that SASR is more sensitive to terrain relief than PSD. Additionally, the critical area is a quantitative index to reflect the stable spatial structure of SASR and PSD in different landforms and may be viewed as the minimum test region of sample areas. The corresponding result of the experiments herein indicated that either spectrum can effectively depict the spatial-temporal distribution of SASR and PSD on Mars under terrain relief and deepen the understanding of the variation of SASR and PSD influences by terrain. The critical area of either spectrum can be employed to explore and determine the stable spatial structure of SASR and PSD in different landforms. The proposed Martian SASR model and the new spectral method theory shed new light on revealing the spatial-temporal structure of SASR and PSD under terrain influences on Mars.

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