On the generation and segregation of helicity in geodynamo simulations

2020 ◽  
Vol 221 (2) ◽  
pp. 741-757
Author(s):  
A Ranjan ◽  
P A Davidson ◽  
U R Christensen ◽  
J Wicht

SUMMARY Helicity, the inner product of velocity and vorticity, is considered an important ingredient for the maintenance of a dipolar magnetic field in the geodynamo. Outside the tangent cylinder—an imaginary cylinder which circumscribes the inner core—a spatial segregation of helicity has been observed in several simulations, being negative in the north and positive in the south. Such a segregation pattern is important for a dynamo that relies on the α-effect. However, the origin of this pattern in these simulations is poorly understood. In this paper, we use three strongly forced numerical dynamo solutions to study the various sources of helicity, including those due to buoyancy $({H_T})$, Coriolis, Lorentz and viscous forces. We find a strong spatial correlation between the segregation pattern of helicity and ${H_T}$ both in the instantaneous and the time-averaged results. Our results show that, outside the tangent cylinder, ${H_T}$ is dominated by the product $- {u_z}\partial T/\partial \varphi $, where ${u_z}$ is the vertical velocity component and T is the temperature perturbation. It is known that when inertial waves are launched from a localized buoyant anomaly, ${H_T}$ takes the same sign as the local helicity. We conjecture that this is the reason for the spatial correlation between ${H_T}$ and helicity in our simulation results. The flow in our simulations being strongly turbulent, this effect seems to be a statistical one and manifests itself most clearly in the averaged quantities.

Author(s):  
Ngô Anh Tú ◽  
Phan Thái Lê ◽  
Nguyễn Hữu Xuân ◽  
Trần Văn Bình

Bài báo xác định lưu lượng dòng chảy theo thời đoạn dựa vào mô hình HEC-HMS, số liệu mưa từ ảnh vệ tinh CHIRPS của NASA và Hệ thống thông tin địa lý (GIS) trong mô phỏng dòng chảy lũ tháng 12 năm 2016 tại lưu vực sông Lại Giang, lưu vực lớn thứ hai của tỉnh Bình Định (sau lưu vực sông Kôn) và có vai trò quan trọng về phát triển kinh tế-xã hội ở phía Bắc của tỉnh. Kết quả mô phỏng dòng chảy lũ rất đáng tin cậy, lưu lượng dòng chảy lũ đạt đỉnh 2542,6 m3/s tương ứng với với tần suất lũ 5%. Chỉ số kiểm định mô hình NSE với giá trị là 0,93; hệ số R2 đạt 0,78 sai số PBIAS khoảng 24% và sai số đỉnh lũ PEC = 52,01.  ABSTRACT The paper aimed to introduce the application of the HEC-HMS hydrological model combination with the CHIRPS (Climate Hazards Group Infrared Precipitation with Station) and GIS to restore flood flow data in the Lai Giang river basin in 2016. The Lai Giang river basin is the second largest basin of Binh Dinh province (after the Kon river basin), it plays an important role in socio-economic development in the North of Binh Dinh province. The simulation results of flood peaks reached 2542,6 m3.s-1 (P=5%). Model test indices such as NSE = 0.93, the correlation coefficient reached 0,78; the percentage of PBIAS error was about 24%, and peak error (PEC) was 52,01.


2019 ◽  
Vol 69 (1) ◽  
pp. 69-84
Author(s):  
Veldurthi Naresh ◽  
D. Bodas ◽  
Chandel Sunil ◽  
Bhave Tejashree

AbstractIn the present work, two geometrically similar passive geometries with dumbbell shape were designed to perturb the dominating viscous forces in the low Reynolds number (Re) flows of the fluids. The geometries were designated as PDM-I and PDM-II, in which all the linear dimensions were related by a constant scale factor of two. Mixing efficiencies and pressure drops of the species at various Reynolds number (Re) were calculated to estimate the scaling effect validations. Finally, the geometrically similar PDM geometries were fabricated in Polydimethylsiloxane (PDMS) polymer to evaluate the scaling effect on the mixing efficiencies of the dyes and validated with the simulation results of species mixing.


2013 ◽  
Vol 70 (1) ◽  
pp. 146-162 ◽  
Author(s):  
Hua Chen ◽  
Da-Lin Zhang

Abstract Previous studies have focused mostly on the roles of environmental factors in the rapid intensification (RI) of tropical cyclones (TCs) because of the lack of high-resolution data in inner-core regions. In this study, the RI of TCs is examined by analyzing the relationship between an upper-level warm core, convective bursts (CBs), sea surface temperature (SST), and surface pressure falls from 72-h cloud-permitting predictions of Hurricane Wilma (2005) with the finest grid size of 1 km. Results show that both the upper-level inertial stability increases and static stability decreases sharply 2–3 h prior to RI, and that the formation of an upper-level warm core, from the subsidence of stratospheric air associated with the detrainment of CBs, coincides with the onset of RI. It is found that the development of CBs precedes RI, but most subsidence warming radiates away by gravity waves and storm-relative flows. In contrast, many fewer CBs occur during RI, but more subsidence warming contributes to the balanced upper-level cyclonic circulation in the warm-core (as intense as 20°C) region. Furthermore, considerable CB activity can still take place in the outer eyewall as the storm weakens during its eyewall replacement. A sensitivity simulation, in which SSTs are reduced by 1°C, shows pronounced reductions in the upper-level warm-core intensity and CB activity. It is concluded that significant CB activity in the inner-core regions is an important ingredient in generating the upper-level warm core that is hydrostatically more efficient for the RI of TCs, given all of the other favorable environmental conditions.


2018 ◽  
Vol 31 (15) ◽  
pp. 5793-5810 ◽  
Author(s):  
Mi-Kyung Sung ◽  
Seon-Hwa Kim ◽  
Baek-Min Kim ◽  
Yong-Sang Choi

This study investigates the origin of the interdecadal variability in the warm Arctic and cold Eurasia (WACE) pattern, which is defined as the second empirical orthogonal function of surface air temperature (SAT) variability over the Eurasian continent in Northern Hemisphere winter, by analyzing the Twentieth Century Reanalysis dataset. While previous studies highlight recent enhancement of the WACE pattern, ascribing it to anthropogenic warming, the authors found that the WACE pattern has experienced a seemingly periodic interdecadal variation over the twentieth century. This long-term variation in the Eurasian SAT is attributable to the altered coupling between the Siberian high (SH) and intraseasonal Rossby wave emanating from the North Atlantic, as the local wave branch interacts with the SH and consequentially enhances the continental temperature perturbation. It is further identified that these atmospheric circulation changes in Eurasia are largely controlled by the decadal amplitude modulation of the climatological stationary waves over the North Atlantic region. The altered decadal mean condition of stationary wave components brings changes in local baroclinicity and storm track activity over the North Atlantic, which jointly change the intraseasonal Rossby wave generation and propagation characteristics as well. With simple stationary wave model experiments, the authors confirm how the altered mean flow condition in the North Atlantic acts as a source for the growth of the Rossby wave that leads to the change in the downstream WACE pattern.


2018 ◽  
Vol 5 (2) ◽  
pp. 119
Author(s):  
I Dewa Gde Yaya Putra Pratama ◽  
I Nyoman Satya Kumara ◽  
I Nyoman Setiawan

In the RUPTL PT PLN Years 2017 untill 2026, the goverment aim to reach 5000 MW of PV plant potential in 2025. But, until November 2016, the number of PV plant in Indonesia is around 11 MW. To reach the 5000 MW target, many approach must be use. One of the approach is install PV plant on goverment buildings. Pusat Pemerintahan Kabupaten Badung (Puspem Badung) is a goverment buildings complex which located in Badung Regency, Bali is one of the goverment building that can be use for this approach. This paper aim to know the potency of electrical power dan electrical energy produced by Puspem Badung if the PV plant installed on the north, east, west, and south side of the roof. Electrical energy produced by PV plant is simulated by using System Advisor Model (SAM). From the simulation results, north side of the roof can produce energy of 1.847.361 kWh/year. From the analysis, the total energy that can be produced by PV plant is 6.169.092 kWh/year. This amount can supply Puspem Badung energy need by 124,72 %.


2008 ◽  
Vol 136 (11) ◽  
pp. 4320-4333 ◽  
Author(s):  
Alexander Lowag ◽  
Michael L. Black ◽  
Matthew D. Eastin

Abstract Hurricane Bret underwent a rapid intensification (RI) and subsequent weakening between 1200 UTC 21 August and 1200 UTC 22 August 1999 before it made landfall on the Texas coast 12 h later. Its minimum sea level pressure fell 35 hPa from 979 to 944 hPa within 24 h. During this period, aircraft of the National Oceanic and Atmospheric Administration (NOAA) flew several research missions that sampled the environment and inner core of the storm. These datasets are combined with gridded data from the National Centers for Environmental Prediction (NCEP) Global Model and the NCEP–National Center for Atmospheric Research (NCAR) reanalyses to document Bret’s atmospheric and oceanic environment as well as their relation to the observed structural and intensity changes. Bret’s RI was linked to movement over a warm ocean eddy and high sea surface temperatures (SSTs) in the Gulf of Mexico coupled with a concurrent decrease in vertical wind shear. SSTs at the beginning of the storm’s RI were approximately 29°C and steadily increased to 30°C as it moved to the north. The vertical wind shear relaxed to less than 10 kt during this time. Mean values of oceanic heat content (OHC) beneath the storm were about 20% higher at the beginning of the RI period than 6 h prior. The subsequent weakening was linked to the cooling of near-coastal shelf waters (to between 25° and 26°C) by prestorm mixing combined with an increase in vertical wind shear. The available observations suggest no intrusion of dry air into the circulation core contributed to the intensity evolution. Sensitivity studies with the Statistical Hurricane Intensity Prediction Scheme (SHIPS) model were conducted to quantitatively describe the influence of environmental conditions on the intensity forecast. Four different cases with modified vertical wind shear and/or SSTs were studied. Differences between the four cases were relatively small because of the model design, but the greatest intensity changes resulted for much cooler prescribed SSTs. The results of this study underscore the importance of OHC and vertical wind shear as significant factors during RIs; however, internal dynamical processes appear to play a more critical role when a favorable environment is present.


2014 ◽  
Vol 51 (8) ◽  
pp. 844-857 ◽  
Author(s):  
S. Firouzianbandpey ◽  
D.V. Griffiths ◽  
L.B. Ibsen ◽  
L.V. Andersen

The main topic of this study is to assess the anisotropic spatial correlation lengths of a sand layer deposit based on cone penetration testing with pore pressure measurement (CPTu) data. Spatial correlation length can be an important factor in reliability analysis of geotechnical systems, yet it is rarely estimated during routine site investigations. Results from two different sites in the north of Denmark are reported in this paper, indicating quite strong anisotropy due to the depositional process, with significantly shorter spatial correlation lengths in the vertical direction. It is observed that the normalized cone resistance is a better estimator of spatial trends than the normalized friction ratio.


2011 ◽  
Vol 139 (6) ◽  
pp. 1708-1727 ◽  
Author(s):  
Yi-Hsuan Huang ◽  
Chun-Chieh Wu ◽  
Yuqing Wang

Abstract High-resolution simulations for Typhoon Krosa (2007) and a set of idealized experiments are conducted using a full-physics model to investigate the eminent deflection of typhoon track prior to its landfall over mountainous island topography. The terrain height of Taiwan plays the most important role in Typhoon Krosa’s looping motion at its landfall, while the surface properties, details in the topographic shape of Taiwan, and the cloud microphysics are shown to be secondary to the track deflection. A simulation with 3-km resolution and realistic model settings reproduces the observed Krosa’s track, while that with 9-km resolution fails, suggesting that high resolution to better resolve the typhoon–terrain interactions is important for the prediction and simulation of typhoon track deflection prior to landfall. Results from idealized experiments with model configurations mimicking those of Supertyphoon Krosa show that vortices approaching the northern and central topography are significantly deflected to the south before making sharp turns to the north, forming a kinked track pattern prior to and during landfall. This storm movement is consistent with the observed looping cases in Taiwan. Both real-case and idealized simulations show strong channel winds enhanced between the storm and the terrain when deflection occurs. Backward trajectory analyses support the concept of the channeling effect, which has been previously found to be crucial to the looping motion of Typhoon Haitang (2005) as well. However, the inner-core asymmetric ventilation flow does not match the movement of a deflected typhoon perfectly, partly because the steering flow is not well defined and could not completely capture the terrain-induced deflection in the simulation and in nature.


1990 ◽  
Vol 59 (4) ◽  
pp. 467-481
Author(s):  
Mark S. Burrows

Few issues have received as much attention and achieved as little consensus among historians of late medieval theology during the past several generations as the debate over the character of “nominalism.” One thrust of the research from this debate has focused on the theological dimensions of this scholastic tradition: building on the work of Erich Hochstetter, Paul Vignaux, and others, Heiko Oberman discussed this development in the North American arena of scholarship by describing theological concerns as “the inner core of nominalism.”1


2020 ◽  
Vol 12 (11) ◽  
pp. 168781402097153
Author(s):  
Ning Meng ◽  
Wang Kun ◽  
Li Mingxin ◽  
Yu Ke ◽  
Wu Zhi

Compared with the rigid hand rehabilitation robot, the soft hand rehabilitation robot has the advantages of good flexibility, which is of great significance to its research. In order to make the soft hand rehabilitation robot have the advantages of high stiffness and simple manufacturing process, a nested structure is proposed for finger soft actuator in this paper. The nested structure consists of outer restraint structure and inner core structure. The inner core structure can realize deformation under the action of air pressure. The outer restraint structure can improve bending efficiency by restraining deformation in non-functional direction of inner core structure. On this basis, the processing technology of nested structure is designed, and the effect of structural parameters on performance is analyzed. In order to illustrate the advantages of nested structure, the performance of nested structure and fiber-constrained structure is compared by simulation, which includes bending angle, gripping force and expansion amount (by measuring the deformation of the cross section). The simulation results show the advantages of the nested structure. A prototype of the soft hand rehabilitation robot is developed with nested structure as finger soft actuator, and the experimental results prove the feasibility of design. The results of this study provide a reference for the structure design of soft hand rehabilitation robot.


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