Link Budget Analysis for Massive-Antenna-Array-Enabled Terahertz Satellite Communications

Broadband satellite communications can enable a plethora of applications in customer services, global nomadic coverage and disaster prediction and recovery. Terahertz(THz) band is envisioned as a key satellite communication technology due to its very broad bandwidth, astrophysical observation advantages and device maturing in recent years. In this paper, a massive-antenna-array-enabled THz satellite communication system is proposed to be established in Tanggula, Tibet, where the average altitude is 5.068 km and the mean-clear-sky precipitable water vapor(PWV) is as low as 1.31 mm. In particular, a link budget analysis(LBA) framework is developed for THz space communications, considering unique THz channel properties and massive antenna array techniques. Moreover, practical siting conditions are taken into account, including the altitude, PWV, THz spectral windows, rain and cloud factors. On the basis of the developed link budget model, the massive antenna array model, and the practical parameters in Tanggula, the performances of signal-to-noise ratio(SNR) and capacity are evaluated. The results illustrate that 1 Tbit/s is attainable in the 0.275~0.37 THz spectral window in Tanggula, by using an antenna array of the size 64.

Link Budget and Networking Analysis of FuTURE 4G TDD Trial System

The FuTURE 4G Time Division Duplex (TDD) trial system uses 3.5 GHz carrier frequency and several crucial technologies including broadband Multiple Input Multiple Output (MIMO) and Orthogonal Frequency Division Multiplexing (OFDM). These technologies challenge the link budget and networking analysis of the FuTURE 4G TDD trial network. This paper analyzes the practical 3.5 GHz propagation model and the link budget of Radio Frequency (RF) parameters of the trial system. Moreover,it introduces networking analysis and network planning of the trial system,which combines the field test results of the MIMO system. The FuTURE 4G TDD trial system and its trial network have been accomplished with successful checkup. The trial system fulfills all the requirements with two Access Points (AP) and three Mobile Terminals (MT),which supports multi-user,mobility,a high peak rate of 100 Mb/s,High-Definition TV (HDTV),high-speed data download,and Voice over IP (VoIP) services.

Freshening of the Intermediate Waters in the Northern South China Sea over the Past Six Decades

The properties of salinity in the South China Sea(SCS),a significant marginal sea connecting the Pacific and Indian Oceans,are greatly influenced by the transport of fresh water flux between the two oceans.However,the long-term changes in the intermediate water in the SCS have not been thoroughly studied due to limited data,particularly in relation to its thermodynamic variations.This study utilized reanalysis data products to identify a 60-year trend of freshening in the intermediate waters of the northern South China Sea(NSCS),accompanied by an expansion of low-salinity water.The study also constructed salinity budget terms,including advection and entrainment processes,and conducted an analysis of the salinity budget to understand the impacts of external and internal dynamic processes on the freshening trend of the intermediate water in the NSCS.The analysis revealed that the freshening in the northwest Pacific Ocean and the intensification of intrusion through the Luzon Strait at intermediate levels are the primary drivers of the salinity changes in the NSCS.Additionally,a weakened trend in the intensity of vertical entrainment also contributes to the freshening in the NSCS.This study offers new insights into the understanding of regional deep sea changes in response to variations in both thermodynamics and oceanic dynamic processes.

Effects of monsoon onset vortex on heat budget in the mixed layer of the Bay of Bengal

We investigated the effects of monsoon onset vortex(MOV)on the mixed layer heat budget in the Bay of Bengal(BOB)in spring 2003 using the reanalysis datasets.The results suggest that the solar radiation flux penetrating the mixed layer and the existence of barrier layer are both able to modulate the effects of MOV on the evolution of sea surface temperature(SST)in the BOB.Prior to the formation of BOB MOV,the local SST raised quickly due to mass of solar radiation reaching the sea surface under the clear-sky condition.Meanwhile,since the mixed layer was shallow before the onset of the Asian summer monsoon(ASM),some solar radiation flux could penetrate to directly heat the deeper water,which partly offset the warming effect of shortwave radiation.On the other hand,the in-situ SST started to cool due to the upwelling of cold water when the MOV generated over the BOB,along with the rapidly increased surface wind speed and its resultant deeper mixed layer.As the MOV developed and moved northward,the SST tended to decrease remarkably because of the strong upward surface latent heat flux over the BOB ascribed to the wind-evaporation mechanism.However,the MOV-related precipitation brought more fresh water into the upper ocean to produce a thicker barrier layer,whose thermal barrier effect damped the cooling effect of entrainment upwelling on the decrease tendency of the BOB SST.In other words,the thermal barrier effect could slow down the decreasing trend of the BOB SST even after the onset of ASM,which facilitated the further enhancement of the MOV.

Modulation of Madden-Julian Oscillation Activity by the Tropical Pacific-Indian Ocean Associated Mode

In this study,the impacts of the tropical Pacific–Indian Ocean associated mode(PIOAM)on Madden–Julian Oscillation(MJO)activity were investigated using reanalysis data.In the positive(negative)phase of the PIOAM,the amplitudes of MJO zonal wind and outgoing longwave radiation are significantly weakened(enhanced)over the Indian Ocean,while they are enhanced(weakened)over the central and eastern Pacific.The eastward propagation of the MJO can extend to the central Pacific in the positive phase of the PIOAM,whereas it is mainly confined to west of 160°E in the negative phase.The PIOAM impacts MJO activity by modifying the atmospheric circulation and moisture budget.Anomalous ascending(descending)motion and positive(negative)moisture anomalies occur over the western Indian Ocean and central-eastern Pacific(Maritime Continent and western Pacific)during the positive phase of the PIOAM.The anomalous circulation is almost the opposite in the negative phases of the PIOAM.This anomalous circulation and moisture can modulate the activity of the MJO.The stronger moistening over the Indian Ocean induced by zonal and vertical moisture advection leads to the stronger MJO activity over the Indian Ocean in the negative phase of the PIOAM.During the positive phase of the PIOAM,the MJO propagates farther east over the central Pacific owing to the stronger moistening there,which is mainly attributable to the meridional and vertical moisture advection,especially low-frequency background state moisture advection by the MJO’s meridional and vertical velocities.

Decadal variation and trend of the upper layer salinity in the South China Sea from 1960 to 2010

Ocean salinity is an essential measurable indicator of water cycle and plays a crucial role in regulating ocean and climate change.Using Simple Ocean Data Assimilation(SODA)reanalysis product,substantial decadal variability of the salinity in the upper layer of the South China Sea(SCS)from 1960 to 2010 was examined.Results show that a decadal variation of the upper layer salinity is clear.The upper layer(100 m)waters are found to freshen from 1960,become saltier during 1975 to 1995,and freshen again from 1995 to 2010.The strongest anomalies appear in the northeastern,northern,and northwestern regions in the three periods,respectively.The salinity variation trends become weaker below the upper layer,except the salinifi cation trend in the northern SCS extends to at least 300 m during the salinifi cation period.Diagnosis of the salinity budget over the top 100 m shows that during the fi rst freshening period horizontal advection,vertical advection,and surface freshwater forcing all contribute to salinity freshening,and horizontal advection is relatively larger.The contribution of horizontal advection and surface freshwater forcing to the positive salinity anomaly is comparable,while the vertical advection is the secondary factor in the salinifi cation period.Horizontal advection,especially zonal advection,plays a crucial role during the second freshening period.Moreover,horizontal advection is more important than that in the fi rst freshening period.In addition,the contribution of horizontal advection is mainly in zonal direction controlled by Kuroshio intrusion.Further analysis shows the upper-layer salinity variations have a Pacifi c Decadal Oscillation(PDO)-like signal,with freshening during the negative PDO years,and salinifi cation during the positive PDO years.PDO mainly infl uences the upper-layer salinity changes through both atmospheric bridge and oceanic bridge.

RADIATIVE AND MICROPHYSICAL EFFECTS OF ICE CLOUDS ON A TORRENTIAL RAINFALL EVENT OVER HUNAN,CHINA

The radiative and microphysical effects of ice clouds on a torrential rainfall event over Hunan,China in June 2004 are investigated by analyzing the sensitivity of cloud-resolving model simulations.The model is initialized by zonally-uniform vertical velocity,zonal wind,horizontal temperature and vapor advection from National Centers for Environmental Prediction(NCEP) /National Center for Atmospheric Research(NCAR) reanalysis data.The exclusion of radiative effects of ice clouds increases model domain mean surface rain rates through the increase in the mean net condensation associated with the increase in the mean radiative cooling during the onset phase and the increases in the mean net condensation and the mean hydrometeor loss during the mature phase.The decrease in the mean rain rate corresponds to the decreased mean net condensation and associated mean latent heat release as the enhanced mean radiative cooling by the removal of radiative effects of ice clouds cools the mean local atmosphere during the decay phase.The removal of microphysical effects of ice clouds decreases the mean rain rates through the decrease in the mean net condensation during the onset phase,while the evolution of mean net condensation and the mean hydrometeor changes from decrease to increase during the mature phase.The reduction in the mean rain rate is primarily associated with the mean hydrometeor change in the absence of microphysical effects of ice clouds during the decay phase.

Double-averaging analysis of turbulent kinetic energy fluxes and budget based on large-eddy simulation

The turbulent flow over a channel bed roughened by three layers of closely packed spheres with a Reynolds number of Re= 15 000 is investigated using the large eddy simulation（LES） and the double-averaging（DA） method. The DA velocity is compared with the results of the corresponding laboratory experiments to validate the LES results. The existence of the types of vortex structures is demonstrated by the Q-criterion above the permeable bed. The turbulent kinetic energy（TKE） fluxes and budget are quantified and discussed. The results show that the TKE fluxes are directed downward and downstream near the virtual bed level. In the TKE budget, the form-induced diffusion rate is significant in the vicinity of the crest bed level, and the TKE production rate and the dissipation rate attain their peaks at the crest bed level and decrease sharply below it.

Exploring HONO formation and its role in driving secondary pollutants formation during winter in the North China Plain

Daytime HONO photolysis is an important source of atmospheric hydroxyl radicals(OH).Knowledge of HONO formation chemistry under typical haze conditions,however,is still limited.In the Multiphase chemistry experiment in Fogs and Aerosols in the North China Plain in 2018,we investigated the wintertime HONO formation and its atmospheric implications at a rural site Gucheng.Three different episodes based on atmospheric aerosol loading levels were classified:clean periods(CPs),moderately polluted periods(MPPs)and severely polluted periods(SPPs).Correlation analysis revealed that HONO formation via heteroge.neous conversion of NO_(2)was more efficient on aerosol surfaces than on ground,highlighting the important role of aerosols in promoting HONO formation.Daytime HONO budget analysis indicated a large missing source(with an average production rate of 0.66±0.26,0.97±0.47 and 1.45±0.55 ppbV/hr for CPs,MPPs and SPPs,respectively),which strongly correlated with photo-enhanced reactions(NO_(2)heterogeneous reaction and particulate nitrate photolysis).Average OH formation derived from HONO photolysis reached up to(0.92±0.71),(1.75±1.26)and(1.82±1.47)ppbV/hr in CPs,MPPs and SPPs respectively,much higher than that from O3 photolysis(i.e.,(0.004±0.004),(0.006±0.007)and(0.0035±0.0034)ppbV/hr).Such high OH production rates could markedly regulate the atmospheric oxidation capacity and hence promote the formation of secondary aerosols and pollutants.

Sustained Decadal Warming Phase in the Southwestern Indian Ocean since the Mid-1990s

Regardless of the slowdown in global warming during the hiatus period, sea surface temperatures(SSTs) in the southwestern Indian Ocean(SWIO) have experienced sustained decadal warming for more than two decades since the mid-1990 s. The SWIO SSTs warmed steadily during 1996–2016, causing a warming hot spot of 0.4 K decade-1 in a large region east of Madagascar. An upper-layer heat budget analysis indicated that heat advection by ocean currents was the greatest contributor to the warming of the SWIO SSTs. The existence of an anticyclonic geostrophic current along the western boundary of the SWIO tended to maintain such warming by transporting warmer water from the west into the SWIO region. In addition, net positive heat transport by ocean currents also occurred at the southern boundary of the SWIO as the climatological northward transport of cold water from the Southern Ocean weakened. This reduction in northward ocean currents at the surface was caused by local wind stress changes, leading to a southward Ekman current. Below the surface, an anticyclonic geostrophic current pattern existed around the warming center near the southeastern SWIO, which reduced the transport of cold waters from the Southern Ocean and warmed the SWIO. These processes near the two boundaries formed a self-sustaining positive feedback mechanism and favored the maintenance of sustained warming in the SWIO. More attention is needed to analyze the sustained long-lasting warming in the SWIO, as it is a unique phenomenon occurring under the background of the ongoing global warming.