Evaluation of three high-resolution satellite precipitation estimates: Potential for monsoon monitoring over Pakistan

Multi-sensor precipitation datasets including two products from the Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA) and estimates from Climate Prediction Center Morphing Technique (CMORPH) product were quantitatively evaluated to study the monsoon variability over Pakistan. Several statistical and graphical techniques are applied to illustrate the nonconformity of the three satellite products from the gauge observations. During the monsoon season (JAS), the three satellite precipitation products captures the intense precipitation well, all showing high correlation for high rain rates (>30 mm/day). The spatial and temporal satellite rainfall error variability shows a significant geo-topography dependent distribution, as all the three products overestimate over mountain ranges in the north and coastal region in the south parts of Indus basin. The TMPA-RT product tends to overestimate light rain rates (approximately 100%) and the bias is low for high rain rates (about ±20%). In general, daily comparisons from 2005 to 2010 show the best agreement between the TMPA-V7 research product and gauge observations with correlation coefficient values ranging from moderate (0.4) to high (0.8) over the spatial domain of Pakistan. The seasonal variation of rainfall frequency has large biases (100–140%) over high latitudes (36N) with complex terrain for daily, monsoon, and pre-monsoon comparisons. Relatively low uncertainties and errors (Bias ±25% and MAE 1–10 mm) were associated with the TMPA-RT product during the monsoon-dominated region (32–35N), thus demonstrating their potential use for developing an operational hydrological application of the satellite-based near real-time products in Pakistan for flood monitoring.     

Variation of hmF2 and NmF2 deduced from DPS-4 over Multan (Pakistan) and their comparisons with IRI-2012 & IRI-2016 during the deep solar minimum between cycles 23 & 24

We report the results of ionospheric measurements from DPS-4 installed at Multan (Geog coord. 30.18°N, 71.48°E, dip 47.4°). The variations in F2-layer maximum electron density NmF2 and its peak height hmF2 are studied during the deep solar minimum between cycles 23 & 24 i.e 2008–2009 with comparisons conducted with the International Reference Ionosphere (IRI) versions 2012 & 2016. We find that the hmF2 observations peak around the pre-sunrise and sunrise hours depending on the month. Seasonally, the daytime variation of NmF2 is higher in the Equinox and Summer, while daytime hmF2 are slightly higher in the Equinox and Winter. High values of hmF2 around midnight are caused by an increase of upward drifts produced by meridional winds. The ionosphere over Multan, which lies at the verge of low and mid latitude, is affected by both $E\times B$ drifts and thermospheric winds as evident from mid-night peaks and near-sunrise dips in hmF2. The results of the comparison of the observed NmF2 and hmF2 for the year 2008–2009 with the IRI-2012 (both NmF2 and hmF2) and IRI-2016 (only hmF2) estimates indicate that for NmF2, IRI-2012 with Consultative Committee International Radio (CCIR) option produces values in better agreement with observed data. Whereas, for hmF2, IRI-2016 with both International Union of Radio Science (URSI) and CCIR SHU-2015 options, predicts well for nighttime hours throughout the year. However, the IRI-2012 with CCIR option produces better agreement with data during daytime hours. Furthermore, IRI-2012 with CCIR option gives better results during Equinox months, whereas, IRI-2016 with both URSI and CCIR SHU-2015 options predict well for Winter and Summer.     

Monitoring spatio-temporal variations in aerosols and aerosol–cloud interactions over Pakistan using MODIS data

Clouds are important elements in climatic processes and interactions between aerosols and clouds are therefore a hot topic for scientific research. Aerosols show both spatial and temporal variations, which can lead to variations in the microphysics of clouds. In this research, we have examined the spatial and temporal variations in aerosol particles over Pakistan and the impact of these variations on various optical properties of clouds, using Moderate Resolution Imaging Spectroradiometer (MODIS) data from the Terra satellite. We used the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model for trajectory analysis to reveal the origins of air masses, with the aim of understanding these spatial and temporal variabilities in aerosol concentrations. We also documented seasonal variations in patterns of aerosol optical depth (AOD) over Pakistan, for which the highest values occur during the monsoon season (June–August). We then analyzed the relationships between AOD and four other cloud parameters, namely water vapour (WV), cloud fraction (CF), cloud top temperature (CTT) and cloud top pressure (CTP). Regional correlation maps and time series plots for aerosol (AOD) and cloud parameters were produced to provide a better understanding of aerosol–cloud interaction. The analyses showed strong positive correlations between AOD and WV for all of the eight cities investigated. The correlation between AOD and CF was positive for those cities where the air masses were predominantly humid, but negative for those cities where the air masses were relatively dry and carried a low aerosol abundance. These correlations were clearly dependent on the meteorological conditions for all of the eight cities investigated. Because of the observed AOD–CF relationship, the co-variation of AOD with CTP and CTT may be attributable to large-scale meteorological variations: AOD showed a positive correlation with CTP and CTT in northern regions of Pakistan and a negative correlation in southern regions.     

Preliminary results of fair-weather atmospheric electric field in the proximity of Main Boundary Thrust,Northern Pakistan

The atmospheric electric Potential Gradient (PG) variation of fair-weather days at Muzaffarabad (MZF, Northern Pakistan) station is presented for the period of January 2015–October 2017. The present investigations focus on the diurnal variation of atmospheric PG on the seasonal and annual time scale. The fair-weather seasonal and annual average PG variation has revealed two peaks, i.e. a primary maximum peak and a secondary maximum peak. The average maximum PG value found is ～410?Vm^?1. The results are then compared with the well-known standard oceanic Carnegie curve. The diurnal curve of PG is found to deviate from the Carnegie curve. The seasonal PG variation at MZF shows lower values during the summer (monsoon) and autumn (post-monsoon) as compared to the winter and spring (pre-monsoon) which could be due to local aerosol concentration. Global comparison of PG (%) values of the annual mean at different longitude, with MZF observatory, shows local morning and evening peaks depicting local sunrise and sunset effects on the PG. The overall outcomes will certainly contribute to further investigate the Global Electric Circuit (GEC).     

Interaction of magnetoacoustic solitons in electron-positron plasmas

The interaction between two, four and six magnetoacoustic solitons in electron-positron plasmas are investigated. The extended Poincaré–Lighthill–Kuo (PLK) perturbation method is employed to derived two KdV equations for magnetoacoustic solitons moving towards each other and studied the head-on collision between them and their phase shifts. The Hirota bilinear method is used to have multi-soliton solutions of already derived two KdV equations for right and left moving solitons. The four and six magnetoacoustic solitons solutions of the two KdV equations are obtained to discuss their interaction and phase shifts. It is found that only compressive magnetoacoustic solitons structures are formed in electron-positron plasma. The present study may be useful to understand the collective phenomena related to head-on and overtaking magnetoacoustic solitons interaction in electron-positron plasmas that may occur in a pulsar magnetosphere.     

角区三维分离流附着鞍点拓扑结构及其演化

实验研究角区层流边界层三维定常分离附着鞍点拓扑结构的存在性及其演化规律.二维粒子图像测速(PIV,Particle Image Velocimetry)激光片光源设置于给定平板和不同模型组成的角区对称面,采用微距镜头捕捉对称面奇点附近的局部流动拓扑结构.实验证实在一定流动参数条件下多种形状模型与平板形成的角区均存在有别于经典分离的附着鞍点拓扑结构;随着雷诺数增加或者随着模型钝度的变化,附着鞍点拓扑结构与经典分离鞍点拓扑结构之间存在着一定的演化规律;对附着鞍点拓扑结构与Lighthill经典三维分离模式的关系进行了分析,表明Lighthill经典三维分离模式也适用于分析附着鞍点拓扑结构.     

Comparison of Ionospheric Total Electron Content (TEC) over Sonmiani (Pakistan) with NeQuick-2 and IRI-2012 during July 2014 – June 2015

In this study, Total Electron Content (TEC) observations acquired by a GNSS receiver installed at Sonmiani (Geog. Coord. 25.19°N, 66.74°E, Geomag. Coord. 17.62°N, 141.5°E) are being reported for the first time. The data utilized is hourly instantaneous TEC values during 10 International Quiet Days (IQDs) per month from Jul-14 to Jun-15, totaling 120 observation days for monitoring nominal TEC. The findings confirm the semi-annual trend of TEC over Sonmiani, which lies at the northern crest of Equatorial Ionization Anomaly (EIA) region. The TEC measurements are then compared with NeQuick-2 and International Reference Ionosphere (IRI-2012) models. It was found that the TEC values derived from NeQuick-2 are in better agreement with GNSS measurements than those from IRI-2012. The TEC measurements also show seasonal variation which is largest during Equinox months. The TEC value in Dec solstice is higher than the Jun solstice, which confirms that the seasonal anomaly is playing a major role in this region during the course of study.     

On the selection of optimal global geopotential model for geoid modeling: A case study in Pakistan

A statistical comparison has been made between gravity field parameters derived from different global geopotential models (GGMs) and observed gravity anomalies, gravimetric geoid and GPS-Leveling data. The motivation behind this study is the selection of best possible global geopotential model that best matches statistically with the local observed data in Pakistan. This will facilitate in decreasing the load on observed data for the development of regional gravimetric geoid in remove-compute-restore technique when used in the Stokes’s integral for computation of the residual part. It is observed that combined geopotential models such as EGM96 and PGM200A, EIGEN-GL04C and EIGEN-CG03C reflect the better match in the total spectral range of gravity and GPS-Leveling data. Results of the precise local geoid model also indicate similar characteristics. A very-high-degree model “EGM2008” (degree/order 2160) exhibits relatively superior statistical fit with observed ground data in Pakistan region. For satellite-only models an increasing trend in the standard deviation can be seen with maximum of about ∼4 m in difference between GPS-Leveling and corresponding GGM’s geoid with increase in the order from 50 to 120 and then it decreases afterwards. However, for the EIGEN-CHAMP03SP, standard deviation saturates to a value of 3.4 m. This is an indication of contamination in the long to medium wavelength part, i.e. 50–100° for the satellite-only models. Moreover, the models DEOS-CHAMP-01C, GGM02C and then ITG-GRACE03 appear to have better fit for medium to long wavelength and can possibly be recommended for use as long wavelength part with the local observed data. While a hybrid geopotential model selection can be achieved through the selection from either of DEOS-CHAMP-01C, GGM02C, GGM02S, EIGEN-GRACE02S or ITG-GRACE03 in the long wavelength (to degree and order 40) and EGM96, PGM200A, EIGEN-GL04C, EIGEN-CG03C or even EGM2008 in medium to short wavelength, i.e. from degree 41 to maximum degree and order.     

A novel autonomous low-cost on-board data handling architecture for a pin-point planetary lander

There has been increased interest in the exploration of the Moon in recent years. Pin-point precision landing is highly desirable for future lunar missions. This paper is concerned with the design of the on-board data handling (OBDH) subsystem for the pin-point lunar lander of the Magnolia-1 project, funded by NASA. Four proposed on-board data handling architectures are outlined and compared in terms of power consumption, performance and reliability. Implementation results are presented, which are obtained from prototyping of the flight computer for the optimal OBDH architecture option on a Xilinx Virtex-5 Field Programmable Gate Array.     

Implications of day temperature variation for an aero-engine's HP turbine-blade's creep life-consumption

Some in-service deterioration in any mechanical device, such as an aero-engine, is inevitable. Also in a country like Pakistan, there is a significant variation of day temperature over the year. As a result of experiencing deterioration (of the engine as a whole or any of its components individually) and/or any alteration in the conditions (such as day temperature) of incoming air stream, an engine will seek a different steady operating point thereby resulting in a variation of the spool speeds and/or turbine-entry temperatures in order to provide the same thrust. Rises in the turbine entry-temperatures and spool speeds result in greater rates of creep and fatigue damage being incurred by the hot-end components and thereby higher engine's life cycle costs.Possessing a better knowledge of the impacts of day temperature variation upon the creep life-consumption of aero-engine's hot-end components, helps the users to take wiser management-decisions. For a military aircraft's mission-profile, using a bespoke computer simulation, the implications of day temperature variation for a turbofan aero-engine's high pressure turbine-blade's creep life-consumption have been predicted.