The annual cycle, intraseasonal oscillations, and roadblock to seasonal predictability of the Asian summer monsoon

Factors responsible for limited predictability of the Asian summer monsoon (ASM) are investigated within a conceptual framework for predictability. Predictability of the seasonal mean depends on the interannual variability (IAV) of the monsoon annual cycle (MAC) and is determined by relative contribution of the predictable "external" component of IAV compared to the unpredictable "internal" IAV. Contributions of slow processes such as those involving air-sea interactions associated with the El Nino-Southern Oscillation (ENSO) or local warm ocean-atmosphere interactions in generating IAV of the MAC are reviewed. Empirical evidence that these air-sea interactions modulate the MAC is presented. Estimates of internal IAV have been made from observations as well as atmospheric model simulations. In contrast to a large part of the Tropics where the summer climate is predictable, with the internal variability being much smaller than the external one, the limited predictability of the Asian monsoon appears to be due to the fact that the contribution from the external IAV over the region is relatively weak and comparable to that from internal IAV. Cause for large internal IAV over the ASM region is investigated, and it is proposed that the internal IAV of the MAC is primarily due to interaction between the MAC and the summer intraseasonal oscillations (ISOs). Two mechanisms through which ISOs lead to internal IAV of the MAC are unraveled. The seasonal bias of the ISO anomalies can influence the seasonal mean if the spatial structure of the ISO has significant projection on that of the seasonal mean and if frequency of occurrence of positive and negative phases is unequal. Evidence supporting this is presented. In addition, it is demonstrated that the chaotic summer ISOs modulated by the annually varying forcing associated with the "slow annual cycle" can lead to IAV of the seasonal mean. Empirical evidence that IAV of ISO activity is related to IAV of the seasonal mean or MAC is also presented. Thus, the Asian monsoon would remain a difficult system to predict. To exploit the predictable signal, however, it is imperative that systematic bias of the models is improved and the space-time structure of the summer ISOs is simulated accurately

Influence of orbital forcing on the seasonality and regionality of the Asian Summer monsoon precipitation

International audienceThe response of Asian monsoon precipitation to contrasting orbital parameters is simulated using the MRI-CGCM climate model. Results show that for the 125 kya B. P. experiment, a large continental heating due to obliquity forcing is apparent and accounts for the strengthened cross equatorial flow, stronger monsoon westerly over the Arabian Sea, and an enhanced precipitation over the Indian subcontinent. For the 115 kya B. P. experiment, while the monsoon westerly becomes weaker in the Arabian Sea, the overall strength of the monsoon westerly becomes stronger in the Bay of Bengal. This eastward extension of the monsoon westerly converges with the equatorial trade wind to give rise to an increased precipitation over the maritime continent and Indochina peninsula. Such increase in precipitation is accompanied with an earlier onset of the Asian monsoon, and an earlier warming of the tropical SST due to precessional forcing. It is concluded that while the obliquity forcing creates the baseline land-sea contrast which maintains the Asian monsoon westerly, when such forcing is comparably weaker, the Indian monsoon is diminished and the precessional forcing becomes more dominating to create a distinct earlier warming of the tropical SST which leads to an earlier onset of the maritime monsoon over the western Pacific. This study implies that even under weaker insolation forcing, the precessional signal may act to enhance certain regional precipitation and onset timing of the Asian monsoon

Naked singularity resolution in cylindrical collapse

In this paper, we study the gravitational collapse of null dust in the cylindrically symmetric spacetime. The naked singularity necessarily forms at the symmetry axis. We consider the situation in which null dust is emitted again from the naked singularity formed by the collapsed null dust and investigate the back-reaction by this emission for the naked singularity. We show a very peculiar but physically important case in which the same amount of null dust as that of the collapsed one is emitted from the naked singularity as soon as the ingoing null dust hits the symmetry axis and forms the naked singularity. In this case, although this naked singularity satisfies the strong curvature condition by Kr\'{o}lak (limiting focusing condition), geodesics which hit the singularity can be extended uniquely across the singularity. Therefore we may say that the collapsing null dust passes through the singularity formed by itself and then leaves for infinity. Finally the singularity completely disappears and the flat spacetime remains.Comment: 17 pages, no figur

Workshop on Monsoon Climate Systems: Toward Better Prediction of the Monsoon

The Earth's monsoon systems are the life-blood of more than two-thirds of the world's population through the rainfall they provide to the mainly agrarian societies they influence. More than 60 experts gathered to assess the current understanding of monsoon variability and to highlight outstanding problems simulating the monsoon

The First Pan-WCRP Workshop on Monsoon Climate Systems: Toward Better Prediction of the Monsoons

In 2004 the Joint Scientific Committee (JSC) that provides scientific guidance to the World Climate Research Programme (WCRP) requested an assessment of (1) WCRP monsoon related activities and (2) the range of available observations and analyses in monsoon regions. The purpose of the assessment was to (a) define the essential elements of a pan-WCRP monsoon modeling strategy, (b) identify the procedures for producing this strategy, and (c) promote improvements in monsoon observations and analyses with a view toward their adequacy, and addressing any undue redundancy or duplication. As such, the WCRP sponsored the ''1st Pan-WCRP Workshop on Monsoon Climate Systems: Toward Better Prediction of the Monsoons'' at the University of California, Irvine, CA, USA from 15-17 June 2005. Experts from the two WCRP programs directly relevant to monsoon studies, the Climate Variability and Predictability Programme (CLIVAR) and the Global Energy and Water Cycle Experiment (GEWEX), gathered to assess the current understanding of the fundamental physical processes governing monsoon variability and to highlight outstanding problems in simulating the monsoon that can be tackled through enhanced cooperation between CLIVAR and GEWEX. The agenda with links to the presentations can be found at: http://www.clivar.org/organization/aamon/WCRPmonsoonWS/agenda.htm. Scientific motivation for a joint CLIVAR-GEWEX approach to investigating monsoons includes the potential for improved medium-range to seasonal prediction through better simulation of intraseasonal (30-60 day) oscillations (ISO's). ISO's are important for the onset of monsoons, as well as the development of active and break periods of rainfall during the monsoon season. Foreknowledge of the active and break phases of the monsoon is important for crop selection, the determination of planting times and mitigation of potential flooding and short-term drought. With a few exceptions simulations of ISO are typically poor in all classes of modeling. Observational and modeling studies indicate that the diurnal cycle of radiative heating and surface fluxes over the ocean are rectified on to the intraseasonal timescale indicating that a synergistic approach to studying monsoon variability is necessary. The diurnal cycle of precipitation and clouds, which directly influence the radiative heating and surface fluxes, are also poorly represented in global models, especially. Thus, it is anticipated that improving the simulation of the diurnal cycle of precipitation and clouds in global models will contribute to an improved ability to simulate ISOs. Improved understanding and simulation of the diurnal cycle is also important since it influences low-levels jets and the associated transport of moisture as well as the rainfall over regions of complex topography

Thermodynamics of four-dimensional black objects in the warped compactification

We reinvestigate the thermodynamics of black objects (holes and strings) in four-dimensional braneworld models that are originally constructed by Emparan, Horowitz and Myers based on the anti-de Sitter (AdS) C-metric. After proving the uniqueness of slicing the AdS C-metric, we derive thermodynamic quantities of the black objects by means of the Euclidean formulation and find that we have no necessity of requiring any regularization to calculate their classical action. We show that there exist the Bekenstein-Hawking law and the thermodynamic first law. The thermodynamic mass of the localized black hole on a flat brane is negative, and it differs from the one previously derived. We discuss the thermodynamic stabilities and show that the BTZ black string is more stable than the localized black holes in a canonical ensemble, except for an extreme case. We also find a braneworld analogue of the Hawking-Page transition between the BTZ black string and thermal AdS branes. The localized black holes on a de Sitter brane is discussed by considering Nariai instanton, comparing the study of "black cigar" in the five-dimensional braneworld model.Comment: 15 pages, 4 figures, RevTex4, typos fixed, minor correction

Experiment and Simulation Effects of Cyclic Pitch Control on Performance of Horizontal Axis Wind Turbine

Offshore wind is generally stronger and more consistent than wind on land. A large part of the offshore wind resource is however located in deep water, where floating wind turbines can harvest more energy. This paper describes a systematic experiment and a simulation analysis (FAST code) about the cyclic pitch control of blades. This work was performed to investigate performance fluctuation of a floating wind turbine utilizing cyclic pitch control. The experiment was carried out in an open wind tunnel with mainstream wind velocity of 10 m/s with the front inflow wind and the oblique inflow wind conditions. A model wind turbine is two-bladed downwind wind turbine with diameter of 1.6 m. Moment and force acts on the model wind turbine were measured by a six-component balance. Fluctuation of power coefficient and thrust coefficient was investigated in the cyclic pitch control. The model wind turbine and the experimental conditions were simulated by FAST code. The comparison of the experimental data and the simulation results of FAST code show that the power coefficient and thrust coefficient are in good agreement. Keywords: Floating Offshore Wind Turbine, Aerodynamic Forces, Cyclic Pitch Control, FAST Code, Wind Tunnel ExperimentArticle History: Received February 11st 2017; Received in revised form April 29th 2017; Accepted June 2nd 2017; Available onlineHow to Cite This Article: Sang, L.Q., Maeda, T., Kamada, Y. and Li, Q. (2017) Experiment and simulation effect of cyclic pitch control on performance of horizontal axis wind turbine to International Journal of Renewable Energy Development, 6(2), 119-125.https://doi.org/10.14710/ijred.6.2.119-12

Thermodynamics of Squashed Kaluza-Klein Black Holes and Black Strings -- A Comparison of Reference Backgrounds --

We investigate thermodynamics constructed on different background reference spacetimes for squashed Kaluza-Klein (SqKK) black hole and electrically charged black string in five-dimensional Einstein-Maxwell system. Two spacetimes are possible to be reference spacetimes giving finite gravitational classical actions: one is four-dimensional Minkowski times a circle and the other is the KK monopole. The boundary of the SqKK black hole can not be matched perfectly to that of the former reference spacetime because of the difference in topology. However, the resultant classical action coincides with that calculated by the counterterm subtraction scheme. The boundary of the KK monopole has the same topology with that of the SqKK black hole and can be matched to the boundary of the black hole perfectly. The resultant action takes different value from the result given by using the former reference spacetime. After a brief review of thermodynamic quantities of the black hole solutions, we calculate thermodynamic potentials relevant for several thermodynamic environments. The most stable state is different for each environment: For example, the KK monopole is the most stable state in isothermal environment with fixed gravitational tension. On the other hand, when the size of the extra-dimension is fixed, the Minkowski times a circle is the most stable. It is shown that these two spacetimes can be reference spacetimes of the five-dimensional black string.Comment: 28 pages; references added, typo corrected;version accepted for publication in Class. Quantum Gra

Xenon-133 and caesium-137 releases into the atmosphere from the Fukushima Dai-ichi nuclear power plant: determination of the source term, atmospheric dispersion, and deposition

On 11 March 2011, an earthquake occurred about 130 km off the Pacific coast of Japan's main island Honshu, followed by a large tsunami. The resulting loss of electric power at the Fukushima Dai-ichi nuclear power plant developed into a disaster causing massive release of radioactivity into the atmosphere. In this study, we determine the emissions into the atmosphere of two isotopes, the noble gas xenon-133 (<sup>133</sup>Xe) and the aerosol-bound caesium-137 (<sup>137</sup>Cs), which have very different release characteristics as well as behavior in the atmosphere. To determine radionuclide emissions as a function of height and time until 20 April, we made a first guess of release rates based on fuel inventories and documented accident events at the site. This first guess was subsequently improved by inverse modeling, which combined it with the results of an atmospheric transport model, FLEXPART, and measurement data from several dozen stations in Japan, North America and other regions. We used both atmospheric activity concentration measurements as well as, for <sup>137</sup>Cs, measurements of bulk deposition. Regarding <sup>133</sup>Xe, we find a total release of 15.3 (uncertainty range 12.2–18.3) EBq, which is more than twice as high as the total release from Chernobyl and likely the largest radioactive noble gas release in history. The entire noble gas inventory of reactor units 1–3 was set free into the atmosphere between 11 and 15 March 2011. In fact, our release estimate is higher than the entire estimated <sup>133</sup>Xe inventory of the Fukushima Dai-ichi nuclear power plant, which we explain with the decay of iodine-133 (half-life of 20.8 h) into <sup>133</sup>Xe. There is strong evidence that the <sup>133</sup>Xe release started before the first active venting was made, possibly indicating structural damage to reactor components and/or leaks due to overpressure which would have allowed early release of noble gases. For <sup>137</sup>Cs, the inversion results give a total emission of 36.6 (20.1–53.1) PBq, or about 43% of the estimated Chernobyl emission. Our results indicate that <sup>137</sup>Cs emissions peaked on 14–15 March but were generally high from 12 until 19 March, when they suddenly dropped by orders of magnitude at the time when spraying of water on the spent-fuel pool of unit 4 started. This indicates that emissions may not have originated only from the damaged reactor cores, but also from the spent-fuel pool of unit 4. This would also confirm that the spraying was an effective countermeasure. We explore the main dispersion and deposition patterns of the radioactive cloud, both regionally for Japan as well as for the entire Northern Hemisphere. While at first sight it seemed fortunate that westerly winds prevailed most of the time during the accident, a different picture emerges from our detailed analysis. Exactly during and following the period of the strongest <sup>137</sup>Cs emissions on 14 and 15 March as well as after another period with strong emissions on 19 March, the radioactive plume was advected over Eastern Honshu Island, where precipitation deposited a large fraction of <sup>137</sup>Cs on land surfaces. Radioactive clouds reached North America on 15 March and Europe on 22 March. By middle of April, <sup>133</sup>Xe was fairly uniformly distributed in the middle latitudes of the entire Northern Hemisphere and was for the first time also measured in the Southern Hemisphere (Darwin station, Australia). In general, simulated and observed concentrations of <sup>133</sup>Xe and <sup>137</sup>Cs both at Japanese as well as at remote sites were in good quantitative agreement. Altogether, we estimate that 6.4 PBq of <sup>137</sup>Cs, or 18% of the total fallout until 20 April, were deposited over Japanese land areas, while most of the rest fell over the North Pacific Ocean. Only 0.7 PBq, or 1.9% of the total fallout were deposited on land areas other than Japan

Preliminary Estimation of Black Carbon Deposition from Nepal Climate Observatory-Pyramid Data and Its Possible Impact on Snow Albedo Changes Over Himalayan Glaciers During the Pre-Monsoon Season

The possible minimal range of reduction in snow surface albedo due to dry deposition of black carbon (BC) in the pre-monsoon period (March-May) was estimated as a lower bound together with the estimation of its accuracy, based on atmospheric observations at the Nepal Climate Observatory-Pyramid (NCO-P) sited at 5079 m a.s.l. in the Himalayan region. We estimated a total BC deposition rate of 2.89 g m-2 day-1 providing a total deposition of 266 micrograms/ square m for March-May at the site, based on a calculation with a minimal deposition velocity of 1.0 10(exp -4) m/s with atmospheric data of equivalent BC concentration. Main BC size at NCO-P site was determined as 103.1-669.8 nm by correlation analysis between equivalent BC concentration and particulate size distribution in the atmosphere. We also estimated BC deposition from the size distribution data and found that 8.7% of the estimated dry deposition corresponds to the estimated BC deposition from equivalent BC concentration data. If all the BC is deposited uniformly on the top 2-cm pure snow, the corresponding BC concentration is 26.0-68.2 microgram/kg assuming snow density variations of 195-512 kg/ cubic m of Yala Glacier close to NCO-P site. Such a concentration of BC in snow could result in 2.0-5.2% albedo reductions. From a simple numerical calculations and if assuming these albedo reductions continue throughout the year, this would lead to a runoff increases of 70-204 mm of water drainage equivalent of 11.6-33.9% of the annual discharge of a typical Tibetan glacier. Our estimates of BC concentration in snow surface for pre-monsoon season can be considered comparable to those at similar altitude in the Himalayan region, where glaciers and perpetual snow region starts in the vicinity of NCO-P. Our estimates from only BC are likely to represent a lower bound for snow albedo reductions, since a fixed slower deposition velocity was used and atmospheric wind and turbulence effects, snow aging, dust deposition, and snow albedo feedbacks were not considered. This study represents the first investigation about BC deposition on snow from atmospheric aerosol data in Himalayas and related albedo effect is especially the first track at the southern slope of Himalayas