scholarly journals A Simple Model for Simulating Tornado Damage in Forests

2006 ◽  
Vol 45 (12) ◽  
pp. 1597-1611 ◽  
Author(s):  
Andrew P. Holland ◽  
Allen J. Riordan ◽  
E. C. Franklin
Keyword(s):  
Simple Model ◽  
Loblolly Pine ◽  
Forward Speed ◽  
Forward Motion ◽  
Tree Resistance ◽  
Forested Areas ◽  
Storm Characteristics ◽  
Tornado Damage ◽  
Cross Track ◽  
Along Track

Abstract An analytical model is presented to describe patterns of downed trees produced by tornadic winds. The model uses a combined Rankine vortex of specified tangential and radial components to describe a simple tornado circulation. A total wind field is then computed by adding the forward motion of the vortex. The lateral and vertical forces on modeled tree stands are then computed and are compared with physical characteristics of Scots and loblolly pine. From this model, patterns of windfall are computed and are compared to reveal three basic damage patterns: cross-track symmetric, along-track asymmetric, and crisscross asymmetric. These patterns are shown to depend on forward speed, radial speed, and tree resistance. It is anticipated that this model will prove to be useful in assessing storm characteristics from damage patterns observed in forested areas.

scholarly journals A two-dimensional Stockwell transform for gravity wave analysis of AIRS measurements

2016 ◽  
Vol 9 (6) ◽  
pp. 2545-2565 ◽  
Author(s):  
Neil P. Hindley ◽  
Nathan D. Smith ◽  
Corwin J. Wright ◽  
D. Andrew S. Rees ◽  
Nicholas J. Mitchell
Keyword(s):  
General Circulation ◽  
Drake Passage ◽  
General Circulation Models ◽  
Two Dimensional ◽  
Atmospheric Infrared Sounder ◽  
Spectral Window ◽  
Energy And Momentum ◽  
Stockwell Transform ◽  
Cross Track ◽  
Along Track

Abstract. Gravity waves (GWs) play a crucial role in the dynamics of the earth's atmosphere. These waves couple lower, middle and upper atmospheric layers by transporting and depositing energy and momentum from their sources to great heights. The accurate parameterisation of GW momentum flux is of key importance to general circulation models but requires accurate measurement of GW properties, which has proved challenging. For more than a decade, the nadir-viewing Atmospheric Infrared Sounder (AIRS) aboard NASA's Aqua satellite has made global, two-dimensional (2-D) measurements of stratospheric radiances in which GWs can be detected. However, one problem with current one-dimensional methods for GW analysis of these data is that they can introduce significant unwanted biases. Here, we present a new analysis method that resolves this problem. Our method uses a 2-D Stockwell transform (2DST) to measure GW amplitudes, horizontal wavelengths and directions of propagation using both the along-track and cross-track dimensions simultaneously. We first test our new method and demonstrate that it can accurately measure GW properties in a specified wave field. We then show that by using a new elliptical spectral window in the 2DST, in place of the traditional Gaussian, we can dramatically improve the recovery of wave amplitude over the standard approach. We then use our improved method to measure GW properties and momentum fluxes in AIRS measurements over two regions known to be intense hotspots of GW activity: (i) the Drake Passage/Antarctic Peninsula and (ii) the isolated mountainous island of South Georgia. The significance of our new 2DST method is that it provides more accurate, unbiased and better localised measurements of key GW properties compared to most current methods. The added flexibility offered by the scaling parameter and our new spectral window presented here extend the usefulness of our 2DST method to other areas of geophysical data analysis and beyond.

Evaluation of Pendulum NGGM Scenarios by Full Closed-Loop Simulation

2021 ◽  
Author(s):  
Florian Wöske ◽  
Benny Rievers
Keyword(s):  
Closed Loop ◽  
Variational Equation ◽  
Satellite Measurement ◽  
Observation Data ◽  
Near Surface ◽  
The Earth ◽  
Cross Track ◽  
Along Track ◽  
Grace Mission ◽  
Gravity Mission

<p>The GRACE mission (2002-2017) delivered temporal gravity field solutions of the Earth for 15 years. It's successor, GRACE follow-on (GRACE-FO) is continuing it's legacy since May 2018. The time series of monthly gravity fields revealed global mass redistribution in in the near surface layer of the Earth with unprecedented accuracy. This assessed a completely new observable in geoscience disciplines and has become a crucial data product for climate research.<br>Despite the groundbreaking success and relevance of the GRACE mission(s) for Earth observation and climate science, no further successor gravity mission is planned, yet. Summarized by the name Next Generation Gravity Mission (NGGM) concepts for future gravimetry missions have been proposed and analyzed for a while. As an outcome of these studies the so called Bender-configuration (two GRACE-like satellite pairs, one in a polar orbit and a second in an inclined orbit around 60° to 70°) is the concept currently favored by the scientific community for a candidate of the next gravity mission to be realized.</p><p><br>However, an other concept still remains interesting due to specific advantages that might contribute to future improvements of gravity missions. In order to emphasize this, we present results of a full closed loop-simulation for a different ll-SST approach, the so called pendulum. It offers a quite similar overall performance with just two satellites. For this configuration the satellites are following each other in orbits with slightly different longitudes of the ascending nodes, thus the inter-satellite measurement direction is varying between along-track and cross-track. This configuration makes an interferometric laser ranging (LRI) quite challenging on the technical level. Nevertheless, the LRI accuracy is not necessarily needed. The relevance of the pendulum configuration has also been shifted into the focus of the French MARVEL mission proposal.</p><p><br>In this contribution we analyze in detail the performance of the pendulum formation with the main parameters being the angle between along-track and cross-track component of the ranging direction at the equator, and the mean distance between the satellites. We conduct the angle variation for different mean ranges and assumed ranging accuracies. As reference, the GRACE and Bender concepts are simulated, as well. The orbit simulations are performed using a derivative of the ZARM/DLR XHPS mission simulator including high precision implementations of non-gravitational accelerations.<br>The different concepts and configurations include complete GRACE-FO like attitude control and realistic environment models. State-of-the-art instrument noise models based on GRACE/-FO are used to generate observation data for accelerometer (ACC), range dependent inter satellite ranging (KBR/LRI), kinematic orbit solution (KOS) and star camera (SCA). For the gravity recovery process we use the classical variational equation approach. As for real GRACE processing, ACC calibration parameter are estimated and KOS and KBR range-rate observations are weighted by VCE.</p>

Hamilton’s Principle, Lagrange’s Method, and Ship Motion Theory

1984 ◽  
Vol 28 (04) ◽  
pp. 229-237 ◽  
Author(s):  
Touvia Miloh
Keyword(s):  
Lagrangian Density ◽  
Transfer Functions ◽  
Equations Of Motion ◽  
Steady Motion ◽  
Harmonic Oscillation ◽  
Wave Radiation ◽  
Forward Speed ◽  
Forward Motion ◽  
Radiation Problem ◽  
Lagrange’S Method

Lagrange's equations of motion, describing the motion of several bodies on or below a free surface, are here derived from Hamilton's variational principle. The Lagrangian density is obtained by extending Luke's principle to the wave-radiation problem, and the hydrodynamical loads on the bodies are expressed in terms of the Lagrangian density and its derivatives with respect to the generalized coordinates of the bodies. First we consider a forced harmonic oscillation without a forward speed and then we discuss the case of the same oscillatory motion superimposed on arbitrary steady motion. In both cases we employ Lagrange's method to derive the transfer functions between the generalized forces and the amplitudes of the harmonic motions, in terms of added mass, damping, and the hydrostatic restoring coefficients. The case of a steady forward motion, for which the transfer function is already known, is obtained as a particular case of the general solution.

scholarly journals Tropical Cyclone Center Fix Using CYGNSS Winds

2019 ◽  
Vol 58 (9) ◽  
pp. 1993-2003 ◽  
Author(s):  
David Mayers ◽  
Christopher Ruf
Keyword(s):  
Wind Speed ◽  
Tropical Cyclone ◽  
Satellite System ◽  
Center Location ◽  
Residual Difference ◽  
Measurement Results ◽  
Storm Center ◽  
Global Navigation Satellite ◽  
Cross Track ◽  
Along Track

AbstractA new method is described for determining the center location of a tropical cyclone (TC) using wind speed measurements by the NASA Cyclone Global Navigation Satellite System (CYGNSS). CYGNSS measurements made during TC overpasses are used to constrain a parametric wind speed model in which storm center location is varied. The “MTrack” storm center location is selected to minimize the residual difference between model and measurement. Results of the MTrack center fix are compared to the National Hurricane Center (NHC) Best Track, the Automated Rotational Center Hurricane Eye Retrieval (ARCHER), and aircraft reconnaissance fixes for category 1–category 3 TCs during the 2017 and 2018 hurricane seasons. MTrack produces storm center locations at intermediate times between NHC fixes with a factor of 5.6 overall reduction in sensitivity to uncertainties in the NHC fixes between which it interpolates. The MTrack uncertainty is found to be larger in the cross-track direction than the along-track direction, although this behavior and the absolute accuracy of position estimates require further investigation.

scholarly journals Ocean Surface Topography Altimetry by Large Baseline Cross-Interferometry from Satellite Formation

2020 ◽  
Vol 12 (21) ◽  
pp. 3519
Author(s):  
Weiya Kong ◽  
Bo Liu ◽  
Xiaohong Sui ◽  
Running Zhang ◽  
Jinping Sun
Keyword(s):  
Surface Topography ◽  
Ocean Surface ◽  
Baseline Length ◽  
Radar Altimeter ◽  
Satellite Formation ◽  
Satellite Platform ◽  
Marine Gravity ◽  
Development Tendency ◽  
Cross Track ◽  
Along Track

Imaging Radar Altimeter (IRA) is the current development tendency for ocean surface topography (OST) altimetry, which utilizes Synthetic Aperture Radar (SAR) and interferometry to improve the spatial resolution of OST to several kilometers or even better. Meanwhile, centimetric altimetry accuracy should be guaranteed for applications such as geostrophic currents or marine gravity anomaly inversion. However, the baseline length of IRA which determines the altimetric sensitivity is confined by the satellite platform, in consideration of baseline vibration and payload capability. Therefore, the baseline length from a single satellite can extend to only tens of meters, making it difficult to achieve centimetric accuracy. Referring to the successful experience from TerraSAR-X/TanDEM-X, satellite formation can easily extend the baseline length to hundreds or thousands of meters, depending on the helix orbit. Therefore, we propose the large baseline IRA (LB-IRA) from satellite formation for OST altimetry: the carrier frequency shift (CFS) is brought in to compensate for the severe baseline decorrelation, and the helix orbit is carefully selected to prevent severe time decorrelation from along-track baseline. The numerical results indicate that the LB-IRA, whose cross-track baseline ranges between 629~1000 m and along-tack baseline ranges between 0~40 m, can achieve ~1 cm relative accuracy at 1 km resolution.

scholarly journals Precise Orbit Determination for GNSS Maneuvering Satellite with the Constraint of a Predicted Clock

2019 ◽  
Vol 11 (16) ◽  
pp. 1949 ◽  
Author(s):  
Xiaolei Dai ◽  
Yidong Lou ◽  
Zhiqiang Dai ◽  
Caibo Hu ◽  
Yaquan Peng ◽  
...  
Keyword(s):  
Orbit Determination ◽  
Precise Orbit Determination ◽  
Satellite System ◽  
Navigation Satellite ◽  
Precise Orbit ◽  
Gps Satellites ◽  
Global Navigation Satellite ◽  
Cross Track ◽  
Along Track ◽  
Backward Integration

Precise orbit products are essential and a prerequisite for global navigation satellite system (GNSS) applications, which, however, are unavailable or unusable when satellites are undertaking maneuvers. We propose a clock-constrained reverse precise point positioning (RPPP) method to generate the rather precise orbits for GNSS maneuvering satellites. In this method, the precise clock estimates generated by the dynamic precise orbit determination (POD) processing before maneuvering are modeled and predicted to the maneuvering periods and they constrain the RPPP POD during maneuvering. The prediction model is developed according to different clock types, of which the 2-h prediction error is 0.31 ns and 1.07 ns for global positioning system (GPS) Rubidium (Rb) and Cesium (Cs) clocks, and 0.45 ns and 0.60 ns for the Beidou navigation satellite system (BDS) geostationary orbit (GEO) and inclined geosynchronous orbit (IGSO)/Median Earth orbit (MEO) satellite clocks, respectively. The performance of this proposed method is first evaluated using the normal observations without maneuvers. Experiment results show that, without clock-constraint, the average root mean square (RMS) of RPPP orbit solutions in the radial, cross-track and along-track directions is 69.3 cm, 5.4 cm and 5.7 cm for GPS satellites and 153.9 cm, 12.8 cm and 10.0 cm for BDS satellites. When the constraint of predicted satellite clocks is introduced, the average RMS is dramatically reduced in the radial direction by a factor of 7–11, with the value of 9.7 cm and 13.4 cm for GPS and BDS satellites. At last, the proposed method is further tested on the actual GPS and BDS maneuver events. The clock-constrained RPPP POD solution is compared to the forward and backward integration orbits of the dynamic POD solution. The resulting orbit differences are less than 20 cm in all three directions for GPS satellite, and less than 30 cm in the radial and cross-track directions and up to 100 cm in the along-track direction for BDS satellites. From the orbit differences, the maneuver start and end time is detected, which reveals that the maneuver duration of GPS satellites is less than 2 min, and the maneuver events last from 22.5 min to 107 min for different BDS satellites.

The Cause of Tone Generation by Aero-Engine Fans at High Subsonic Tip Speeds and the Effect of Forward Speed

1974 ◽  
Vol 96 (3) ◽  
pp. 228-234 ◽  
Author(s):  
N. A. Cumpsty ◽  
B. W. Lowrie
Keyword(s):  
Boundary Layer ◽  
Forward Speed ◽  
Flow Distortion ◽  
Forward Motion ◽  
Inlet Guide Vanes ◽  
Wall Boundary Layer ◽  
Aero Engine ◽  
Mach Numbers ◽  
Static Conditions ◽  
Tone Generation

Modern aero-engine fans (without inlet guide vanes) produce a tone at blade passing frequency by interacting with the inlet flow distortion. Because the distortion is altered by forward motion of the aircraft the tone is also different under static and inflight conditions. At low tip relative Mach numbers (less than about 0.85) the significant source of distortion is the intake wall boundary layer. At higher tip Mach numbers the principal distortion under static conditions is the atmospheric turbulence drawn into the intake, but in flight this reduces and other forms of distortion may then dominate.

scholarly journals Comments on “A Simple Model for Simulating Tornado Damage in Forests”

2008 ◽  
Vol 47 (2) ◽  
pp. 726-731 ◽  
Author(s):  
Nikolai Dotzek ◽  
Richard E. Peterson ◽  
Bernold Feuerstein ◽  
Martin Hubrig
Keyword(s):  
Simple Model ◽  
Tornado Damage

scholarly journals Using kinetic energy measurements from altimetry to detect shifts in the positions of fronts in the Southern Ocean

Ocean Science ◽  
2018 ◽  
Vol 14 (1) ◽  
pp. 105-116 ◽  
Author(s):  
Don P. Chambers
Keyword(s):  
Kinetic Energy ◽  
Southern Ocean ◽  
Current System ◽  
Sea Surface ◽  
Significant Shift ◽  
Dynamic Topography ◽  
Circumpolar Current ◽  
Cross Track ◽  
Along Track ◽  
The Antarctic

Abstract. A novel analysis is performed utilizing cross-track kinetic energy (CKE) computed from along-track sea surface height anomalies. The midpoint of enhanced kinetic energy averaged over 3-year periods from 1993 to 2016 is determined across the Southern Ocean and examined to detect shifts in frontal positions, based on previous observations that kinetic energy is high around fronts in the Antarctic Circumpolar Current system due to jet instabilities. It is demonstrated that although the CKE does not represent the full eddy kinetic energy (computed from crossovers), the shape of the enhanced regions along ground tracks is the same, and CKE has a much finer spatial sampling of 6.9 km. Results indicate no significant shift in the front positions across the Southern Ocean, on average, although there are some localized, large movements. This is consistent with other studies utilizing sea surface temperature gradients, the latitude of mean transport, and the probability of jet occurrence, but is inconsistent with studies utilizing the movement of contours of dynamic topography.

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