Minimum Surface Pressure Research Articles

AN AUTOMATIC SATELLITE INTERPRETATION OF TROPICAL CYCLONE PATTERNS USING ELASTIC GRAPH DYNAMIC LINK MODEL

In the past decades, satellite interpretation was one of the vital methods for the determination of weather patterns all over the world, especially for the identification of severe weather patterns such as tropical cyclones (TC). The method is based on Dvorak Technique8 which provides a means of the identification of the cyclone and its intensity. This is a kind of pattern-matching techniques and is based on some well-known TC templates for reference. Due to the high variation and complexity of cloud activities for the tropical cyclone patterns, meteorological analysts all over the world so far are still relying on subjective human justification for TC identification purposes. In this paper, an Elastic Graph Dynamic Link Model (EGDLM) is proposed to automate the satellite interpretation process and provides an objective analysis for tropical cyclones. The method integrates Dynamic Link Architecture (DLA) for neural dynamics and Active Contour Model (ACM) for contour extraction of TC patterns. Over 120 satellite pictures provided by National Oceanic and Atmospheric Administration (NOAA) were used to evaluate the system, and 145 tropical cyclone cases that appeared in the period between 1990 to 1998 were extracted for the study. An overall correct rate for TC classification was found to be above 95%. For hurricanes with distinct "eye" formation, the model reported a deviation within 3 km from the "actual eye" location, which was obtained from the reconnaissance aircraft measurements of minimum surface pressure.

The dynamics of heat lows

A numerical model is used to investigate dynamical aspects of the structure and evolution of a heat low in an idealized flow configuration with an area of land surrounded by sea. of particular interest is the evolution of the distributions of relative vorticity and potential vorticity. While the heat low has a minimum surface pressure in the late afternoon following strong solar heating of the land, the relative vorticity is strongest in the early morning hours following a prolonged period of low-level convergence. Thus the heat low is not approximately in quasi-geostrophic balance. the low-level convergence is associated with the sea-breeze and later with the nocturnal low-level jet. the effects of differing sea area, land area and Coriolis parameter on various aspects of the heat low are investigated. Although a cyclonic vortex, the heat low is characterized by an anticyclonic potential-vorticity anomaly relative to its environment throughout much of the lower troposphere on account of the greatly reduced static stability in the convectively well-mixed boundary layer; however, the surface temperature maximum over land corresponds with a cyclonic potential-vorticity anomaly at the surface. the reduced static stability in the mixed layer has the further consequence that the horizontal components of relative vorticity and horizontal potential-temperature gradient make a non-negligible contribution and of opposite sign to the potential vorticity in certain flow regions. Two processes associated with the flow evolution in the model appear to be fundamental to understanding a range of low-level atmospheric phenomena over the arid interior of Australia: these are the deep convective mixing over land during the daytime and the development of a nocturnal low-level jet, which leads to convergence in the trough. Such phenomena include the diurnal behaviour of dry cold fronts and the generation of nocturnal wind surges and bores. It is reasonable to assume that similar processes operate in other arid regions of the world where deep convective mixing over land produces local maxima of diabatic heating in the lower atmosphere.

The dynamics of heat lows

AbstractA numerical model is used to investigate dynamical aspects of the structure and evolution of a heat low in an idealized flow configuration with an area of land surrounded by sea. of particular interest is the evolution of the distributions of relative vorticity and potential vorticity. While the heat low has a minimum surface pressure in the late afternoon following strong solar heating of the land, the relative vorticity is strongest in the early morning hours following a prolonged period of low‐level convergence. Thus the heat low is not approximately in quasi‐geostrophic balance. the low‐level convergence is associated with the sea‐breeze and later with the nocturnal low‐level jet. the effects of differing sea area, land area and Coriolis parameter on various aspects of the heat low are investigated.Although a cyclonic vortex, the heat low is characterized by an anticyclonic potential‐vorticity anomaly relative to its environment throughout much of the lower troposphere on account of the greatly reduced static stability in the convectively well‐mixed boundary layer; however, the surface temperature maximum over land corresponds with a cyclonic potential‐vorticity anomaly at the surface. the reduced static stability in the mixed layer has the further consequence that the horizontal components of relative vorticity and horizontal potential‐temperature gradient make a non‐negligible contribution and of opposite sign to the potential vorticity in certain flow regions.Two processes associated with the flow evolution in the model appear to be fundamental to understanding a range of low‐level atmospheric phenomena over the arid interior of Australia: these are the deep convective mixing over land during the daytime and the development of a nocturnal low‐level jet, which leads to convergence in the trough. Such phenomena include the diurnal behaviour of dry cold fronts and the generation of nocturnal wind surges and bores. It is reasonable to assume that similar processes operate in other arid regions of the world where deep convective mixing over land produces local maxima of diabatic heating in the lower atmosphere.

Development of an Objective Scheme to Estimate Tropical Cyclone Intensity from Digital Geostationary Satellite Infrared Imagery

The standard method for estimating the intensity of tropical cyclones is based on satellite observations (Dvorak technique) and is utilized operationally by tropical analysis centers around the world. The technique relies on image pattern recognition along with analyst interpretation of empirically based rules regarding the vigor and organization of convection surrounding the storm center. While this method performs well enough in most cases to be employed operationally, there are situations when analyst judgment can lead to discrepancies between different analysis centers estimating the same storm. In an attempt to eliminate this subjectivity, a computer-based algorithm that operates objectively on digital infrared information has been developed. An original version of this algorithm (engineered primarily by the third author) has been significantly modified and advanced to include selected “Dvorak rules,” additional constraints, and a time-averaging scheme. This modified version, the Objective Dvorak Technique (ODT), is applicable to tropical cyclones that have attained tropical storm or hurricane strength. The performance of the ODT is evaluated on cases from the 1995 and 1996 Atlantic hurricane seasons. Reconnaissance aircraft measurements of minimum surface pressure are used to validate the satellite-based estimates. Statistical analysis indicates the technique to be competitive with, and in some cases superior to, the Dvorak-based intensity estimates produced operationally by satellite analysts from tropical analysis centers. Further analysis reveals situations where the algorithm needs improvement, and directions for future research and modifications are suggested.

Simulations of the Atmospheres of Synchronously Rotating Terrestrial Planets Orbiting M Dwarfs: Conditions for Atmospheric Collapse and the Implications for Habitability

Planets within the habitable zones of M dwarfs are likely to be synchronous rotators; in other words, one side is permanently illuminated while the other side is in perpetual darkness. We present results of three-dimensional simulations of the atmospheres of such planets, and comment on their possible habitability. Near the ground, a thermally direct longitudinal cell exists, transporting heat from the dayside to the nightside. The circulation is three-dimensional, with low-level winds returning mass to the dayside across the polar regions. Aloft, the zonally averaged winds display a pattern of strong superrotation due to these planets' finite (albeit small) rotation rate. With terrestrial values of insolation, a CO2/H2O atmosphere collapses, or condenses on the surface of the darkside, when surface pressure is approximately 30 mb, this value being much lower for a N2atmosphere. This temperature contrast is also sensitive to factors such as gravity, planetary radius, and IR optical depth τ. These results question the suitability of the concept of a habitable zone around M dwarfs that is independent of planetary parameters. If CO2partial pressure is controlled by the carbonate–silicate cycle, we find that these planets should have a minimum surface pressure of 1000–1500 mb of CO2, as this is the minimum pressure needed to support stable liquid water on the darkside at the inner edge of the habitable zone. We finally conclude that planets orbiting M stars can support atmospheres over a large range of conditions and, despite constraints such as stellar activity, are very likely to be habitable.

Tropical cyclone simulation with Emanuel’s convection scheme

ABSTRACT. A new convection parameterization scheme proposed by Emanuel (1991) is used to simulate the evolution of tropical cyclone. The numerical model used for this study is a 19 level axi-symmetric primitive equation, hydrostatic model in a z co-ordinate system. The vertical domain ranges from 0 to 18 km and the horizontal domain ranges upto 3114 km with a resolution of 20 km. in the central 400 km radius and with increasing radial distance thereafter.
 The evolution of an initially balanced vortex with an initial strength of 9 m/sec is studied. It is shown that Emanuel's convection scheme is successful in simulating the development of the initial vortex into a mature, intense cyclonic storm. At the mature stage, a minimum surface pressure of 930 hPa is attained with the associated low level maximum tangential wind speed of 70 m/sec. The simulated circulation features at the mature stage show the formation of an intense cyclone.
 
 Two different sensitivity experiments were performed. A set of experiments with the variation of sea surface temperature (SST) from 300.5° to 302° K in steps of 0.5° K have shown that the intensity of model cyclone increases with the increase of SST. Another set of experiments with variation of latitude has shown that the cyclonic storm is more intense at lower latitudes.
 

A note on strong mass loss from early sun and warm and wet Mars

Recently, the possibility of strong mass loss from an early sun has been proposed in connection with the lithium depletion problem along with early solar system problems. However, the time scale for this enhanced mass loss is uncertain. Using an empirical relation for the dependence of the Martian surface temperature on solar luminosity and surface pressure, we find that the mass loss time scale for a 1.1 M⊙ sun should be about 1 × 109 years or longer if Mars had liquid water on its surface 3.8 billion years ago. The minimum surface pressure on early Mars should be about 5 bars of CO2.

Tropical Cyclone Simulations with the Betts Convective Adjustment Scheme. Part I: Model Description and Control Simulation

Abstract A new convective parameterization scheme proposed by Betts is tested in a tropical cyclone model. The convective adjustment scheme adjusts the local temperature and moisture structures towards the observed quasi-equilibrium thermodynamic state and includes nonprecipitating shallow convection as well as deep convection. The numerical model used for this study is an axisymmetric, primitive equation, hydrostatic, finite difference model with 15 vertical levels and a horizontal resolution of 20 km. The spectral radiation boundary condition, which uses a different gravity wave speed for each vertical mode, is implemented in the model. It is shown that the convective scheme is capable of simulating the developing, rapidly intensifying, and mature stages of a tropical cyclone from a weak vortex. At the mature stage, the minimum surface pressure and maximum low level tangential wind speed are around 923 mb and 58 m s−1. During the early developing stage, the latent heat release is from the convective par...

A Numerical Study of the East Coast Snowstorm of 10–12 February 1983

A numerical study of the East Coast snowstorm of 10–12 February 1983 has been conducted with the NRL mesoscale model. The three-dimensional, hydrostatic, primitive equation model has 91 × 51 horizontal grid points with a half degree resolution in a verification domain of 100°W to 60°W and 25°N to 45°N. There are ten layers in the vertical of equal σ(=p/ps) thickness. The model uses a split-explicit method for temporal integration and a second-order accurate spatial finite differencing. Model physics include precipitation on the resolvable scale and parameterized boundary layer and cumulus convection. The NMC 2.5 degree hemispheric analyses are used as the basic dataset (called NMC analysis hereafter). Because significant details in the initial conditions contained in the original rawinsonde observations may have been smoothed out by the NMC analysis algorithm, the analyses are also altered to provide a closer fit to the rawinsonde data. Original rawinsonde data are used in this enhancement of the NMC analyses (called enhanced). Forecasts are made from both the NMC analysis and the enhanced analyses to determine whether the enhancement can improve the forecasts. The Barnes analysis scheme with parameters suitable for reducing the short wavelength noise on the model grid scale is used to enhance the NMC analyses with the original soundings. Three types of lateral boundary treatments—constant, tendency damping, and temporal relaxation boundary conditions—are tested and compared. Results from forecast experiments show that the boundary treatment has a great impact on the model performance. The constant boundary condition produces an unusable forecast after 12 h as judged by the S1 scores, while the relaxation boundary condition produces an excellent forecast. The enhancement of the initial conditions has a negligible effect on predictions when reasonable boundary updates are used for the snowstorm case. The enhanced dataset produces a slightly better but still useless forecast when constant boundary conditions are used. Numerical experiments have also been conducted to test the sensitivity of the cyclogenesis to physical processes by suppressing one or more physical processes in the model. It is found that the evaporation from the ocean modulates the location and amount of precipitation. Without the evaporation, the-intensity of the cyclone remains the same but the center stays on the coast instead of staying off shore. The track of the snowstorm is such that the sensible beating from the ocean dampens the development of the cyclone by reducing the low-level baroclinicity. Without the sensible heating, the minimum surface pressure of the cyclone is 11 mb lower. The latent heating is found to be important for this case in which the maximum beating rate is 15°–20°C/day. When latent heating is suppressed, the cyclone translates at a much reduced rate and its central pressure is 10 mb higher after two days of simulation. These results from the sensitivity tests are of course case-dependent.

Surface respreading after collapse of monolayers containing major lipids of pulmonary surfactant

Isotherms have been obtained near 37°C for a series of repetitive compressions and expansions of monolayers that contain major components of lung surfactant. The minimum surface tension or maximum surface pressure which could be achieved under conditions of dynamic compression, and the rate of return of lipid from excluded phase to the monolayers were measured. Monolayers of pure 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC), or of DPPC plus 10 or 30 mol% of the calcium salt of 1-palmitoyl-2-oleoyl- sn-glycero-3-phospho- rac-glycerol (POPG) (POPG-Ca) achieved very high surface pressures or low surface tensions (near 0 mN m −1), but they showed no return of material from the collapse phases under the test conditions. Monolayers of POPG-Ca alone collapsed at relatively low surface pressures (high surface tensions), but showed good return of material from the collapse phase into the monolayer. Monolayers containing more complex mixtures of lipids (DPPC, phosphatidylglycerol (PG), unsaturated phosphatidylcholine (PC), cholesterol (chol)) in ratios similar to those found in surfactant achieved minimum surface tensions intermediate between those of monolayers with less complex compositions. These more complex mixtures showed a better rate of return of lipids from the collapse phases to the monolayer than did simple DPPC-POPG mixtures. 31P-NMR and differential scanning calorimetric investigations of the mixture DPPC/1-palmitoyl-2-oleoyl- sn-glycero-3-phosphocholine(POPC)/POPG/DPPG/chol (10:4:2:1:3) showed that in the bulk phase at 37°C, it was in bilayers in the liquid-crystalline state.

A Comparison of Large and Small Tropical Cyclones

In this paper the climatology and structure of, and possible reasons for, tropical cyclones of different sizes are examined. The climatology of tropical cyclone sizes confirms that tropical cyclones of the western North Pacific are characteristically twice as large as their Atlantic counterparts, and also reveals that the typical size of tropical cyclones varies seasonally and regionally and is only weakly correlated with cyclone intensity (maximum surface wind or minimum surface pressure). Rawinsonde composities of large and small tropical cyclones show that large cyclones have much more relative angular momentum (RAM) than small cyclones, while the differences in RAM between intense and weaker cyclones of equivalent size are less. Some of the implications of this observance are discussed, and a hypothesis that cyclones grow as a result of an increased convergence of angular momentum forced by their environment is presented.

Prediction of Maximum Flow Rates From Geopressured Aquifers

Summary Three methods were developed to predict production history of a geopressured aquifer with surface pressure maintained at a constant, minimal value. Production of a geopressured aquifer in this manner would accelerate the recovery of the energy and thereby maximize its present value. The first technique is centered around the exponential integral solution to the diffusivity equation. The constantly changing flow rate is approximated in a stepwise fashion using the principle of superposition. The effects of aquifer boundaries are included by the addition of image wells to create a rectangular aquifer with the well located at any position within the aquifer. The second technique uses the semisteady-state solution to the diffusivity equation. As before, the constantly changing flow rate is approximated in a stepwise fashion. The effects of aquifer boundaries are included by assuming that the reservoir is circular with the well located at its center. The third technique uses the terminal-pressure, limited-reservoir solution to the diffusivity equation. This technique differs from the other two in that the constantly changing bottomhole pressure (BHP) is approximated in a stepwise fashion using superposition. As in the semisteady-state solution, a circular reservoir with the well located at its center is assumed. The three techniques were applied to two typical south Louisiana geopressured aquifers. Predicted production rates from all three techniques were essentially equal. A sensitivity analysis of the various parameters indicates that production rates are most sensitive to tubing size, formation damage, and those parameters that dictate ultimate possible water recovery, such as PV and initial pressure. Introduction To determine the economic feasibility of producing geopressured aquifers for energy, several investigators have utilized simplified reservoir engineering techniques to predict aquifer behavior during production. These techniques assume an arbitrary, constant flow rate, and the well is produced at this rate until the surface pressure falls to some limiting value. The rate then can be reduced and production continued until the limiting pressure is once again reached. While these previous investigations provided valuable information, the use of a constant flow rate in determining the rate of energy production can decrease the present value of the energy by spreading the production over a long time span. In practice, the optimal flow rate from a geopressured aquifer for a given development scheme could be the maximum possible flow rate. The maximum production rate is realized if a well is produced with the minimum surface pressure possible. The resulting flow rate and BHP would decrease continuously with time, making treatment by simplified reservoir engineering techniques impossible. The optimal development scheme would maximize the present value, requiring both a reservoir engineering study using the described techniques and an economic study. This would consider development and operating costs as well as the income from methane production. This type study would optimize the number of wells and the size of wellbores, and would consider the effects of different well spacings. The scope of this paper is limited to the adaptation of well-known solutions to the diffusivity equation to the treatment of the case where both flow rate and BHP decrease continuously with time. A follow up paper by Quitzau and Bassiouni considers the economics of geopressured energy using one of the techniques discussed in this paper and Monte Carlo simulation. Development of Equations During production of a geopressured aquifer, the surface pressure at any given time is equal to the aquifer pressure near the wellbore less any pressure drop caused by formation damage (skin), and less hydrostatic and frictional losses in the tubing string:The pressure drop caused by skin damage can be found bySince gas will be coming out of solution as the pressure is reduced in the flow string, the frictional and hydrostatic pressure loss terms have to be estimated with one of the numerous two-phase flow correlations available for that purpose. Most of these correlations are documented by Brill and Beggs. Note that these correlations were developed for flow rates and flow path sizes that are much smaller than these required for optimal exploitation of a geopressured well. JPT P. 503^

A Strongly Coupled, Fully Implicit, Three-Dimensional, Three-Phase Well Coning Model

Abstract WELCOS is a robust, three-dimensional, three-phase well coning simulator that couples the well rate equation to the reservoir flow equations. This strong coupling allows well rate to be determined simultaneously with reservoir pressures and saturations. The flexibility obtained permits the use of dynamic constraints on well rates, resulting in a highly stable model. The model may be used to obtain the maximum well productivity for a given set of physical limitations and regulatory constraints – e.g., minimum surface pressure, maximum allowed GOR, WOR, water rate, gas rate, etc. The model can function either as a production well or an injection well and, in general, may be used to study any single-well behavior. This paper describes a strongly coupled formulation and discusses its utility in relation to other implicit models. The linearization of the nonlinear finite difference equations and solution of the resulting linear equations are discussed. Example field applications are included to show the utility of user-supplied production constraints in determining well performance.

A Numerical Simulation Study on the Genesis of a Tropical Storm

The genesis of a tropical storm is studied using a numerical simulation model. The model used is an 11-level primitive equation model covering a channel domain of 25° span with open lateral boundaries at latitudes 5.5 and 30.5°N. The initial basic flow field is based on the mean condition at 80°W during Phase III of GATE. The superposed wave disturbance is initially confined in the lower troposphere. The time integration of the model is carried out to 96 h, during which a tropical storm develops accompanied by an upper level anticyclone. The genetic sequence of the disturbance system, from a shallow easterly wave into a tropical depression and further into a tropical storm, is described. The minimum surface pressure of the system deepens from 1008.4 to 1002.6 mb at 96 h. The maximum surface wind at 96 h is above 17 m s−1. The relative vorticity at 950 mb intensifies from 43 × 10−6 s−1 at the initial time to 237 × 10−6 s−1 at 96 h. The surface convergence increases from 24 × 10−6 10−6 s−1 to 71 × 10−6 s−1. The processes involved in the above transformation are extensively discussed. Attention is given to the change in the area of rainfall and cloud from a zonal pattern to a cluster-type, the deepening of the cloud within the system, the appearance of horizontal tilt of the trough axis and the time variation of its vertical tilt, the evolution of the vertical motion field, the thickening of the convergence layer around the depression center, the formation of a warm core at 335 mb and its downward extension, the appearance of a cold core at a higher level, etc. The intensification of the vortex and the growth of a warm core are analyzed by examining the budgets of vorticity and heat at the tropical depression stage. The vorticity increase at low levels is due to stretching of the vortex. Relative horizontal advection causes a decrease of vorticity in some outer areas. At upper levels, the upward protrusion of positive vorticity from below and relative horizontal advection cause a positive tendency. Both the effect due to horizontal divergence and the twisting up of a horizontal vortex make negative contributions. The net effect at upper levels is to produce a compact positive vorticity area within a large region of negative vorticity. Upper level warming is largely due to the excess of the condensation-convection heating over the cooling effect associated with the upward motion. The appearance of an upper level disturbance in the present model is caused entirely by the forcing from below. Supplemental experiments confirm that, although the diabatic heating effect of radiation plays an important role, the heating due to the condensation of water vapor is essential for the formation of a tropical storm in the present case.

A note on dynamics of the eye of typhoon

In the course of the author's re-examination of the existing theories to illustrate the dynamical origin of the eye of typhoon, his attention is paid to Kuo's formula to determine the radius of the eye by observable or presumable data, and he shows that the same result can be obtained by a different method, i. e. introducing a balanced circular vortex governed by the gradient wind equation with an adiabatically flowing circulation system of Ferrel's and having a positive value of the minimum surface pressure which appears near the center.

Characteristics of North African Easterly Waves During the Summers of 1968 and 1969

Abstract This study uses both spectral and compositing analyses to determine the structure of North African easterly waves during the summers of 1968 and 1969. The average period and wavelength computed by the power-spectrum method are 4.5 days and 3800 km and for the compositing analysis 3.8 days and 3100 km. Although the period and wavelength of individual waves vary considerably, the spectral results are in qualitative agreement with the compositing results except in extreme northern Africa where eastward-moving disturbances of the same period affect the spectral computations. The maximum surface amplitudes of u, v, p and Td associated with the waves occur about 20N near the mean location of the east-west oriented region of minimum surface pressure. East of the Greenwich meridian the amplitude decreases and the wave motion is barely detectable with surface data near 25E. The compositing results show that the waves influence latitudes between 5 and 3ON and that wave features tilt from southwest to north...