1,337 research outputs found
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Constraining the evolution and origin of methane plumes on Mars
Future trace gas observations by the Nadir and Occultation for Mars Discovery (NOMAD) and Atmospheric Chemistry Suite (ACS) instruments on the ExoMars Trace Gas Orbiter (TGO) spacecraft will be the first instruments able to provide vertical profiles of multiple trace gas species, including methane. For interpretation and understanding of the retrieved methane vertical profiles, modelling studies are required to scrutinise between the different proposed mechanisms of methane release into the atmosphere, with global circulations models (GCMs) providing an invaluable tool to investigate the evolution of trace gas plumes and provide constraints on where the original source could be located, and potentially clues to its origin.
This study investigates the vertical evolution of methane from multiple different source emission scenarios, using the state-of-the-art LMD-UK Mars GCM coupled to the Analysis Correction assimilation scheme. For the methane emission scenarios in this study, temperature retrievals from the Thermal Emission Spectrometer are assimilated. With the assimilation scheme ensuring the wind fields are consistent with the thermal data input to the model, the assimilation process ensures the optimal dynamical state of the atmosphere and subsequently the best constraint on the transport of tracers in the martian atmosphere.
We show that at methane release rates constrained by previous observations and modelling studies, discriminating whether the methane source is a sustained or instantaneous surface emission requires at least ten sols of tracking the emission. A methane source must also be observed within five to ten sols of the initial emission to distinguish whether the emission occurs directly at the surface or within the atmosphere via destabilisation of metastable clathrates. The added constraint on global winds by the assimilation of thermal data is critical when attempting to backtrack the methane to its original source location
Wide Area Monitoring and Control
Today\u27s interconnected power system is deregulated for wholesale power transfers. In 1996 Federal Energy Regulatory Commission provided open access of the transmission network to utilities. Since then utilities are transferring power over long distances to bring reliable and economical electric supply to their customers. As the number of wholesale power transactions taking place over an interconnected system are increasing, system operators in control areas are forced to monitor the grid on a large scale to operate it reliably. Before scheduling such a large scale power transactions, it is necessary to make sure that such transaction will not violate system operating steady state security limits such as transmission line-flow limits and bus voltage limits. The ideal solution to this problem is to consider entire interconnected system as one system to monitor it. However, this solution is technically expensive if not impossible and hindered by confidentiality issues. This research aims to develop tools that help the system operators to operate the deregulated power grid reliably. State estimation is the tool used by today\u27s energy control centers to develop a base case of the system in real-time, which is further used to study the impact of disturbances and power transactions on static and dynamic security limits of the system. In order to monitor the deregulated power system, a wide area state estimator is required. In this dissertation a two-level approach to achieve such a solution is presented. This way, individual areas are allowed to run their own state estimator, without exchanging any real-time data with neighbor areas. The central coordinator then coordinates state estimator results available from individual areas to bring them to a global reference. This dissertation also presents the application of measurements from GPS synchronized phasor measurement units to improve accuracy of two-level state estimator. In addition to monitoring, system operators also need to determine that if they can allow the scheduled transaction to take place. This requires them to determine transfer capability of the system in real-time. This dissertation presents new iterative transfer capability algorithm which can be used in real-time. As an interconnected system is deregulated and the power transactions are taking place through many control areas, a system wide solution of transfer capability is required. This dissertation presents a two-level framework similar to one used for state estimation to achieve multi-area transfer capability solution. In general, the research work carried out would help in improving power system reliability and operation
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Modelling Radiatively Active Water Ice Clouds in the Martian Water Cycle
The aim of this project is to model the Martian water cycle, including radiatively active water ice clouds, to interpret new observations from Mars Climate Sounder. We will be using the latest version of the LMD MGCM, which includes the new LMD physics routines. A unique data assimilation system will be used to obtain a complete, dynamically self-consistent reconstruction of the entire global circulation for the complete period of the MCS mission to date.
From the produced records, a series of diagnostic studies will then be made to characterise the climatology and synoptic meteorology of Mars over seasonal and interannual timescales, including detailed case studies of events such as the formation of cyclonic weather systems. The assimilation results can be used to test the validity of the new cloud schemes introduced to the model, which will improve our understanding of the Martian water cycle
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Assimilation of Mars Climate Sounder Dust Observations: Challenges and Ways Forward
Introduction: Atmospheric dust is ubiquitous on Mars, and as a result of its absorption and scattering of radiation, is the key driver of the martian circulation. Accurately representing the complex spatial and temporal distribution of dust is therefore crucial for understanding Marsâ atmospheric dynamics. In particular, the vertical representation of the dust distribution in Marsâ atmosphere has been shown to have a significant effect on results from modelling and assimilation [1,2,3]. With the goal of more accurately representing this distribution, the assimilation of dust vertical information is a valuable technique which is being increasingly explored [4,5]. However, it brings with it its own challenges and methodological questions to be explored.
Model and assimilation details: We use the LMD-UK Mars Global Circulation Model (MGCM), which solves the meteorological primitive equations of fluid dynamics, radiative and other parameterised physics to calculate the state of the martian atmosphere [6,7]. The UK version of the MGCM possesses a spectral dynamical core and semi-Lagrangian advection scheme [8], and is a collaboration between the Laboratoire de MĂ©tĂ©orologie Dynamique, The Open University, the University of Oxford, and the Instituto de Astrofisica de Andalucia. The model was run using a range of spectral and vertical resolutions, the latter spaced logarithmically. The assimilation scheme used was a modified version of the Analysis Correction scheme developed at the Met Office [9], adapted for use on Mars [10]. This method has the advantage of being computationally in-expensive, and its use of repeated insertion, weighted over a time window of about six hours, helps counter the issue of relaxation of the atmospheric state â an especially significant problem given the low thermal inertia of Marsâ atmosphere.
Retrievals: The retrievals used in this study are from the Mars Climate Sounder (MCS) instrument aboard the Mars Reconnaissance Orbiter (MRO) [11], which now has amassed over five full martian yearsâ worth of data. For this study, the assimilated MCS variables were temperature and dust profiles. Temperature profiles extend from the surface to approximately 100 km, and dust profiles from as low as 10 km above the surface up to a maximum height of approximately 50 km. Retrieval of dust profiles allows MCS to observe the complex vertical dust structure in the atmosphere. The retrieval version used is 5.2, a re-processing using updated 2D geometry [12]. This results in improved retrievals, especially in the polar regions.
While not used in this study, the NOMAD instrument aboard ExoMars TGO will soon provide another high-volume source of dust profiles alongside MCS [13], and should return observations with an even higher vertical resolution.
Discussion: The assimilation of MCS dust profiles poses unique technical challenges, but presents the opportunity of representing Marsâ vertical dust distribution with unprecedented spatial and temporal accuracy within a GCM. Some outstanding questions for further experimentation and discussion include:
What are the optimal spatial and, in particular, vertical model resolutions for assimilation of this data?
Can dust profile assimilation aid in forecasting? Previous indirect assimilation of vertical dust via its MCS temperature signature has yielded a forecast time of 10 sols [5]; how dependent is this on the assimilation scheme and the choice of assimilating variables?
How should we approach the bimodal nature of MCS local times? Should we give higher weighting to nightside dust observations, which tend to have better vertical coverage due to reduced scattering? And how much can we validly infer from the high day-night variability seen in MCS dust profiles?
What are the best heuristics for filtering spurious opacities which could disrupt the assimilation, for example due to CO2 ice or surface reflectance [16])?
What are the optimal ways of dealing with spatial and temporal gaps in the dataset?
How can we best represent the dust distribution beyond the range of MCS, especially in the lowest 5-10 km of the atmosphere?
What are the advantages and disadvantages of directly assimilating the dust field vs indirectly up-dating the dust field via its temperature signature, as seen in Fig. 1?
Dust profile assimilation has been used to track individual dust storm events [4]; what can this tell us about storm formation and evolution, and can it be used for storm forecasting?
How can we best constrain and validate the column optical depths of MCS dust profiles?
Some ways forward regarding these questions will be explored, including comparative reanalyses and validation against different orbital datasets. Comparisons against MCS and other retrievals (such as NOMAD) should provide insight into the advantages of various in-model representations of features such as the dust distribution as well as the possible advantages or disadvantages of pruning the assimilated dataset. Meanwhile, alternate orbital or even ground-based sources of column opacity (such as Mars Express and MSL) could help better con-strain the distribution of dust not seen by MCS and offer clues how best to proceed in periods when MCS data is missing or limited. Some results of intercomparisons will be presented with the aim of fostering a more general discussion on MCS assimilation techniques.
References: [1] Lewis, S. R. et al., Icarus 192 (2), 327-347, 2007. [2] Rogberg, P. et al., QJRMS 136, 1614-1635, 2010. [3] Greybush, S. J. et al., JGR. 117, E11008, 2012. [4] Ruan, T., DPhil Thesis, 2015. [5] Navarro T. et al., Earth and Space Sci., 2017. [6] Forget, F. et al., JGR 104, 24155-24175, 1999. [7] Madeleine, J.-B. et al., JGR (Planets) 116, E11010, 2011. [8] Newman, C. E. et al., JGR 107, 5123, 2002. [9] Lorenc, A. C. et al., QJRMS 117, 59-89, 1991. [10] Lewis, S. R. et al., Icarus 192, 327-347, 2007. [11] McCleese, D. J. et al., J. Geophys. Res. 115, E12016, 2010. [12] Kleinböhl, A. et al., J. Quant. Spectrosc. Radiat. Transfer 187, 511-522, 2017. [13] Patel, M. R. et al., Appl. Opt. 56 (10), 2771-2782, 2017. [14] Navarro, T. et al., Geophys. Res. Lett. 41, 6620-6626, 2014. [15] Streeter, P. M. et al., 6th Intl. Workshop on the Mars Atmosphere, 2017. [16] Kleinböhl, A. et al., Icarus 261, 118-121, 2015
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ASSIMILATION OF MARTIAN OZONE
Observations of atmospheric ozone on Mars can be used to develop the representation of trace gas transport, sources and sinks within global circulation models and constrain middle atmosphere wind speeds which are not observed directly. Ozone is also readily destroyed by OH which recycles CO2 to provide global stability of the atmosphere, a process still not fully understood.
To make optimal use of information, observations and model information are combined by the process of data assimilation. Although data assimilation is now commonplace on Earth, it is a fairly new concept for other planetary systems, with Mars the only other current candidate. The satellites currently orbiting Mars, combined with the future planned satellite missions, create a great opportunity for the development of trace gas data assimilation techniques for extraterrestrial planets.
For this project we use the LMD/UK Martian Global Circulation Model. The model uses a UK spectral dynamical core and transport scheme from a collaboration between the Open University and Oxford University along with physical parameterisations [6] primarily developed by the Laboratoire de MeÌteÌorologie Dynamique and Instituto de AstrofiÌsica de AndaluciÌa. Combined with the LMD photochemical module and the UK Analysis Correction scheme tuned for Mars for assimilation of observations, we can investigate the evolution of ozone throughout a Martian year.
Preliminary results are discussed from investigation of the adjusted model ozone abundance while testing a method of assimilating artificial ozone data. Once refined, the technique will then be used for the assimilation of real observations from the SPICAM and MARCI instruments which provide total ozone column abundance
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Modelling the ultraviolet environment at the surface of Mars and design of the Beagle 2 UV sensor
This thesis describes a multi-layer radiative transfer UV model which was used to aid in the design of the UV sensor on Beagle 2, which will soon provide the first ever in situ measurement of UV flux at the martian surface. The model uses the delta-Eddington approximation for diffuse flux and new low temperature gas absorption cross-sections and aerosol optical properties. Dust, H2O clouds and morning fogs are found to modify the martian surface UV spectrum. Dust storms have been shown to attenuate the surface UV flux by more than an order of magnitude, though some UV persists even at extremely high optical depths. The seasonal variation of surface UV irradiance was found to produce maximum exposure areas highly dependent upon dust activity over the martian year. Dust activity is also shown to distort the annual latitudinal dose, with high dust loading in the southern hemisphere resulting in a higher annual dose than in the north. The introduction of O3 abundances of 1.64 x 1017cm-2 into the model resulted in only partial protection for micro-organisms, since wavelengths shorter than 230 nm still penetrate to the surface. DNA-weighting of a martian UV spectrum shows the surface UV environment to be 103 times more damaging than on Earth. UV detection signatures of atmospheric
phenomena and anticipated events for the case of Beagle 2 are presented: a dust devil encounter creates a double minimum profile in the UV flux, and solar eclipses by Phobos produce a single minimum. Clouds increase the diffuse/direct UV ratio, and fogs create a distinct dip in the morning profile when normalised to clear days
Analysis of Liquidity Management in Petroleum Industry of India (With Special Reference to Refining Companies)
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