scholarly journals Growth of Circulation around Supercell Updrafts

2004 ◽  
Vol 61 (23) ◽  
pp. 2863-2876 ◽  
Author(s):  
Robert Davies-Jones
Keyword(s):  
Propagation Velocity ◽  
Linear Part ◽  
Vertical Wind Shear ◽  
Rate Of Change ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Nonlinear Part ◽  
Beltrami Flow ◽  
Local Propagation ◽  
Rate Of Increase

Abstract A formula is derived for the rate of change of circulation around an updraft perimeter at a constant elevation. This quantity depends on the continuous propagation of points on the edge, so an expression for local propagation of the edge is obtained from Petterssen's formula for the motion of an isopleth and the vertical equation of motion. On the edge of an updraft in inviscid anelastic flow, the local propagation velocity along the outward normal is equal to the local nonhydrostatic vertical pressure-gradient force (NHVPGF) divided by the magnitude of the local vertical-velocity gradient. Circulation around an updraft perimeter increases at a rate equal to the line integral around the edge of vertical vorticity times the outward propagation velocity. Formulas are also found for the propagation of an updraft's centroid at a given height and for the acceleration of an updraft's vertical helicity. All of the formulas are tested on exact Beltrami-flow solutions of the governing equations. The relevance of two paradigms of supercell dynamics to local edge propagation and circulation growth of updrafts is evaluated by decomposing the NHVPGF into linearly and nonlinearly forced parts and examining results of supercell simulations in different types of shear. Propagation across the shear and rate of increase of circulation depend mostly on the nonlinear part of the NHVPGF (as in the vertical-wind-shear paradigm) for updrafts in nearly unidirectional shear and on the linear part (as in the helicity paradigm) for updrafts in shear that turns markedly with height.

scholarly journals Sensitivity of Hurricane Intensity Forecast to Convective Momentum Transport Parameterization

2006 ◽  
Vol 134 (2) ◽  
pp. 664-674 ◽  
Author(s):  
Jongil Han ◽  
Hua-Lu Pan
Keyword(s):  
Wind Shear ◽  
Vertical Wind Shear ◽  
Momentum Transport ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Momentum Exchange ◽  
Forecast System ◽  
Hurricane Intensity ◽  
Convective Momentum Transport ◽  
The Many

Abstract A parameterization of the convection-induced pressure gradient force (PGF) in convective momentum transport (CMT) is tested for hurricane intensity forecasting using NCEP's operational Global Forecast System (GFS) and its nested Regional Spectral Model (RSM). In the parameterization the PGF is assumed to be proportional to the product of the cloud mass flux and vertical wind shear. Compared to control forecasts using the present operational GFS and RSM where the PGF effect in CMT is taken into account empirically, the new PGF parameterization helps increase hurricane intensity by reducing the vertical momentum exchange, giving rise to a closer comparison to the observations. In addition, the new PGF parameterization forecasts not only show more realistically organized precipitation patterns with enhanced hurricane intensity but also reduce the forecast track error. Nevertheless, the model forecasts with the new PGF parameterization still largely underpredict the observed intensity. One of the many possible reasons for the large underprediction may be the absence of hurricane initialization in the models.

scholarly journals Remote Trigger of Deep Convection by Cold Outflow over the Taiwan Strait in the Mei-Yu Season: A Modeling Study of the 8 June 2007 Case

2011 ◽  
Vol 139 (9) ◽  
pp. 2854-2875 ◽  
Author(s):  
Chung-Chieh Wang ◽  
George Tai-Jen Chen ◽  
Shin-Yi Huang
Keyword(s):  
Heavy Rainfall ◽  
Deep Convection ◽  
Vertical Wind Shear ◽  
Taiwan Strait ◽  
Heavy Rainfall Event ◽  
Positive Pressure ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Near Surface ◽  
Cold Air

In this study, the heavy-rainfall event over central Taiwan during the mei-yu season on 8 June 2007 is investigated, with an emphasis on the triggering mechanism for the deep convection that produced the rain. Observations indicate that there existed two lines of forcing with convection prior to the rain: one over the northern Taiwan Strait along the mei-yu front and the other over the southern Taiwan Strait. Yet, the convection in question developed over the central strait between these two lines, in an unstable environment with strong westerly vertical wind shear. This motivated the authors to carry out the present study. The Cloud-Resolving Storm Simulation (CReSS) of Nagoya University was used and the event was reproduced at a horizontal grid size of 2 km, including the initiation of new convection over the central strait at the correct location and time. The model results suggest a crucial role played by the series of active, persistent, and propagating storms in the southern strait (along the aforementioned second forcing line). On their back (northern) side, these storms repeatedly produced pulses of cold outflow that traveled toward the north-northeast with positive pressure perturbation. With characteristics of gravity waves, the perturbation propagated faster than the cold air and the associated increase in forward-directed (horizontal) pressure gradient force led to northward acceleration of near-surface flow (by up to 4–5 m s−1 h−1). The stronger southerly flow in turn enhanced downstream convergence, and the deep convection was triggered in the central strait near the arrival of the gravity wave ahead of the cold air. When the convection moved eastward over Taiwan, heavy rainfall resulted. The mechanism presented here for remote triggering of convection over the ocean has not been documented near Taiwan during the mei-yu season. With a better understanding about the behavior of convection, these results can contribute to the improvement of quantitative precipitation forecasts and hazard prevention and reduction.

scholarly journals The forces exerted by aquatic suction feeders on their prey

2007 ◽  
Vol 4 (14) ◽  
pp. 553-560 ◽  
Author(s):  
Peter C Wainwright ◽  
Steven W Day
Keyword(s):  
Pressure Gradient ◽  
Prey Item ◽  
Fluid Velocity ◽  
Lepomis Macrochirus ◽  
Gradient Force ◽  
Spatial Gradient ◽  
Pressure Gradient Force ◽  
Suction Feeding ◽  
Rate Of Increase ◽  
Suction Flow

Successful prey capture by aquatic suction feeders depends on the ability of the predator to generate a flow of water external to the mouth that overcomes any movements and forces that the prey uses to resist the suction flow. Elucidating the nature and magnitude of these forces is a key to understanding what limits suction feeding performance. We identify three potential forces produced by the suction flow field: drag, acceleration reaction and the fluid pressure gradient. Using a mathematical model parametrized with empirical data from feeding bluegill, Lepomis macrochirus , we explore the relative magnitude of these forces under three encounter scenarios with a 5 mm diameter, spherical prey: an immobile mid-water prey; a similar prey that executes an escape response; and a prey item that grips a substratum. Contrary to the almost exclusive emphasis on drag in the suction feeding literature, it made a minor contribution to the total forces in all three cases. In all three scenarios, the pressure gradient is the largest of the three forces. These results are important because previous researchers have emphasized drag and have not explicitly recognized a role for the pressure gradient force in suction feeding. The simulations suggest previously unrecognized mechanisms that suction feeders can use to enhance the forces that they exert, by increasing the steepness of the pressure gradient that the prey item is exposed to. This can be accomplished either by increasing the rate of increase in fluid velocity or by restricting the size of the mouth aperture, which creates a steeper spatial gradient in pressure.

Forecasting of Summer Monsoon Rainfall over Gangetic West Bengal, India Utilising Intrinsic Mode Functions, Linear and Neural Regression

2020 ◽  
Vol 12 (1) ◽  
pp. 60-69 ◽  
Author(s):  
Pijush Basak
Keyword(s):  
Neural Network ◽  
West Bengal ◽  
Monsoon Rainfall ◽  
Linear Part ◽  
Intrinsic Mode Functions ◽  
Quasi Biennial Oscillation ◽  
Nonlinear Part ◽  
South West ◽  
South West Monsoon ◽  
West Monsoon

The South West Monsoon rainfall data of the meteorological subdivision number 6 of India enclosing Gangetic West Bengal is shown to be decomposable into eight empirical time series, namely Intrinsic Mode Functions. This leads one to identify the first empirical mode as a nonlinear part and the remaining modes as the linear part of the data. The nonlinear part is modeled with the technique Neural Network based Generalized Regression Neural Network model technique whereas the linear part is sensibly modeled through simple regression method. The different Intrinsic modes as verified are well connected with relevant atmospheric features, namely, El Nino, Quasi-biennial Oscillation, Sunspot cycle and others. It is observed that the proposed model explains around 75% of inter annual variability (IAV) of the rainfall series of Gangetic West Bengal. The model is efficient in statistical forecasting of South West Monsoon rainfall in the region as verified from independent part of the real data. The statistical forecasts of SWM rainfall for GWB for the years 2012 and 2013 are108.71 cm and 126.21 cm respectively, where as corresponding to the actual rainfall of 93.19 cm 115.20 cm respectively which are within one standard deviation of mean rainfall.

scholarly journals Hemogram as marker of in-hospital mortality in COVID-19

2021 ◽  
pp. jim-2021-001810
Author(s):  
Alejandro López-Escobar ◽  
Rodrigo Madurga ◽  
José María Castellano ◽  
Santiago Ruiz de Aguiar ◽  
Sara Velázquez ◽  
...  
Keyword(s):  
Hospital Mortality ◽  
Hospital Admission ◽  
White Blood Cells ◽  
Rate Of Change ◽  
Hospital Death ◽  
Direct Role ◽  
Lymphocyte Ratio ◽  
Risk Of Death ◽  
Rate Of Increase ◽  
Increased Risk

The clinical impact of COVID-19 disease calls for the identification of routine variables to identify patients at increased risk of death. Current understanding of moderate-to-severe COVID-19 pathophysiology points toward an underlying cytokine release driving a hyperinflammatory and procoagulant state. In this scenario, white blood cells and platelets play a direct role as effectors of such inflammation and thrombotic response. We investigate whether hemogram-derived ratios such as neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio and the systemic immune-inflammation index may help to identify patients at risk of fatal outcomes. Activated platelets and neutrophils may be playing a decisive role during the thromboinflammatory phase of COVID-19 so, in addition, we introduce and validate a novel marker, the neutrophil-to-platelet ratio (NPR).Two thousand and eighty-eight hospitalized patients with COVID-19 admitted at any of the hospitals of HM Hospitales group in Spain, from March 1 to June 10, 2020, were categorized according to the primary outcome of in-hospital death.Baseline values, as well as the rate of increase of the four ratios analyzed were significantly higher at hospital admission in patients who died than in those who were discharged (p<0.0001). In multivariable logistic regression models, NLR (OR 1.05; 95% CI 1.02 to 1.08, p=0.00035) and NPR (OR 1.23; 95% CI 1.12 to 1.36, p<0.0001) were significantly and independently associated with in-hospital mortality.According to our results, hemogram-derived ratios obtained at hospital admission, as well as the rate of change during hospitalization, may easily detect, primarily using NLR and the novel NPR, patients with COVID-19 at high risk of in-hospital mortality.

scholarly journals Temporal evolution of the momentum balance terms and frictional adjustment observed over the inner shelf during a storm

Ocean Science ◽  
2016 ◽  
Vol 12 (1) ◽  
pp. 137-151 ◽  
Author(s):  
M. Grifoll ◽  
A. L. Aretxabaleta ◽  
J. L. Pelegrí ◽  
M. Espino
Keyword(s):  
Coriolis Force ◽  
Wind Stress ◽  
Water Depth ◽  
Momentum Balance ◽  
Wave Radiation ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Inner Shelf ◽  
Coastal Waves ◽  
Nw Mediterranean

Abstract. We investigate the rapidly changing equilibrium between the momentum sources and sinks during the passage of a single two-peak storm over the Catalan inner shelf (NW Mediterranean Sea). Velocity measurements at 24 m water depth are taken as representative of the inner shelf, and the cross-shelf variability is explored with measurements at 50 m water depth. During both wind pulses, the flow accelerated at 24 m until shortly after the wind maxima, when the bottom stress was able to compensate for the wind stress. Concurrently, the sea level also responded, with the pressure-gradient force opposing the wind stress. Before, during and after the second wind pulse, there were velocity fluctuations with both super- and sub-inertial periods likely associated with transient coastal waves. Throughout the storm, the Coriolis force and wave radiation stresses were relatively unimportant in the along-shelf momentum balance. The frictional adjustment timescale was around 10 h, consistent with the e-folding time obtained from bottom drag parameterizations. The momentum evolution at 50 m showed a larger influence of the Coriolis force at the expense of a decreased frictional relevance, typical in the transition from the inner to the mid-shelf.

scholarly journals High-resolution glacial and deglacial record of atmospheric methane by continuous-flow and laser spectrometer analysis along the NEEM ice core

2013 ◽  
Vol 9 (6) ◽  
pp. 2579-2593 ◽  
Author(s):  
J. Chappellaz ◽  
C. Stowasser ◽  
T. Blunier ◽  
D. Baslev-Clausen ◽  
E. J. Brook ◽  
...  
Keyword(s):  
High Resolution ◽  
Continuous Flow ◽  
Ice Core ◽  
Rate Of Change ◽  
Atmospheric Methane ◽  
Data Set ◽  
Rate Of Increase ◽  
Concentration Changes ◽  
Cross Dating ◽  
Laser Spectroscopic

Abstract. The Greenland NEEM (North Greenland Eemian Ice Drilling) operation in 2010 provided the first opportunity to combine trace-gas measurements by laser spectroscopic instruments and continuous-flow analysis along a freshly drilled ice core in a field-based setting. We present the resulting atmospheric methane (CH4) record covering the time period from 107.7 to 9.5 ka b2k (thousand years before 2000 AD). Companion discrete CH4 measurements are required to transfer the laser spectroscopic data from a relative to an absolute scale. However, even on a relative scale, the high-resolution CH4 data set significantly improves our knowledge of past atmospheric methane concentration changes. New significant sub-millennial-scale features appear during interstadials and stadials, generally associated with similar changes in water isotopic ratios of the ice, a proxy for local temperature. In addition to the midpoint of Dansgaard–Oeschger (D/O) CH4 transitions usually used for cross-dating, sharp definition of the start and end of these events brings precise depth markers (with ±20 cm uncertainty) for further cross-dating with other palaeo- or ice core records, e.g. speleothems. The method also provides an estimate of CH4 rates of change. The onsets of D/O events in the methane signal show a more rapid rate of change than their endings. The rate of CH4 increase associated with the onsets of D/O events progressively declines from 1.7 to 0.6 ppbv yr−1 in the course of marine isotope stage 3. The largest observed rate of increase takes place at the onset of D/O event #21 and reaches 2.5 ppbv yr−1.

scholarly journals Increasing surface ozone concentrations in the background atmosphere of Southern China, 1994–2007

2009 ◽  
Vol 9 (16) ◽  
pp. 6217-6227 ◽  
Author(s):  
T. Wang ◽  
X. L. Wei ◽  
A. J. Ding ◽  
C. N. Poon ◽  
K. S. Lam ◽  
...  
Keyword(s):  
Hong Kong ◽  
South China ◽  
Surface Ozone ◽  
Eastern China ◽  
Rate Of Change ◽  
Urban Site ◽  
Coastal Regions ◽  
Air Masses ◽  
Background Ozone ◽  
Rate Of Increase

Abstract. Tropospheric ozone is of great importance with regard to air quality, atmospheric chemistry, and climate change. In this paper we report the first continuous record of surface ozone in the background atmosphere of South China. The data were obtained from 1994 to 2007 at a coastal site in Hong Kong, which is strongly influenced by the outflow of Asian continental air during the winter and the inflow of maritime air from the subtropics in the summer. Three methods are used to derive the rate of change in ozone. A linear fit to the 14-year record shows that the ozone concentration increased by 0.58 ppbv/yr, whereas comparing means in years 1994–2000 and 2001–2007 gives an increase of 0.87 ppbv/yr for a 7-year period. The ozone changes in air masses from various source regions are also examined. Using local wind and carbon monoxide (CO) data to filter out local influence, we find that ozone increased by 0.94 ppbv/yr from 1994–2000 to 2001–2007 in air masses from Eastern China, with similar changes in the other two continent-influenced air-mass groups, but no statistically significant change in the marine air. An examination of the nitrogen dioxide (NO2) column obtained from GOME and SCIAMACHY reveals an increase in atmospheric NO2 in China's three fastest developing coastal regions, whereas NO2 in other parts of Asia decreased during the same period, and no obvious trend over the main shipping routes in the South China Sea was indicated. Thus the observed increase in background ozone in Hong Kong is most likely due to the increased emissions of NO2 (and possibly volatile organic compounds (VOCs) as well) in the upwind coastal regions of mainland China. The CO data at Hok Tsui showed less definitive changes compared to the satellite NO2 column. The increase in background ozone likely made a strong contribution (81%) to the rate of increase in "total ozone" at an urban site in Hong Kong, suggesting the need to consider distant sources when developing long-term strategies to mitigate local ozone pollution.

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