Negative Surface Pressure Research Articles

Role of tropical-extratropical interactions in the unprecedented 2022 extreme rainfall in Pakistan: A historical perspective

Pakistan experienced widespread floods that associated with two intraseasonal rainfall events in July–August 2022, resulting in significant loss of life and property. The study investigates the impact of tropical-extratropical interactions on extreme intraseasonal rainfall events over Pakistan in boreal summer. The intraseasonal rainfall events are identified and classified into extreme and moderate types based on their amplitudes. Both types of rainfall events were associated with the northward propagating Boreal Summer Intraseasonal Oscillation (BSISO). However, extreme events were accompanied by less coherent northward propagation of BSISO than moderate events. The Silk Road Pattern (SRP) teleconnection plays a critical role in extreme rainfall events over Pakistan. During extreme events, positive geopotential height anomalies and anticyclonic circulation at 200 hPa are observed in association with the slowly eastward and southward evolutions of the SRP. Positive temperature anomalies associated with the positive geopotential height anomalies extend southwestward from the upper-level to the low-level, leading to low-level heating and negative surface pressure over the Iran plateau. They further induce low-level moisture flux convergence and upward vertical motions over Pakistan, resulting in extreme rainfall. These features are not apparent during moderate events. The extratropical signals associated with the July 2022 intraseasonal rainfall event are similar to those composited results of extreme rainfall events, while reversed signals were observed for the August 2022 event. The outcomes of this study suggest that the intraseasonal variations of the SRP are crucial precursors for extreme rainfall over Pakistan.

Spatial Variation in the Synoptic Structure of Convective Systems over the Great Plains

Abstract During the summer, rainfall over the Rocky Mountains peaks in the afternoon. The diurnal time of maximum rain becomes progressively delayed in going eastward from the Rocky Mountains, such that over much of the Great Plains, maximum rain occurs near 0300 local time. We use Rapid Refresh (RAP) reanalysis data from July and August of 2009–19 to show that there is continuous spatial variation in the mean structure of the high-rain events that occur along this anomalous diurnally propagating rainfall feature. High-rain events that occur farther from the Rockies are more likely to be associated with a larger warm anomaly to the south of the rain event center, a smaller cold anomaly, a larger negative surface pressure anomaly, and increased low-level southerly meridional wind. We also use the Integrated Multi-Satellite Retrievals for GPM (IMERG) rainfall dataset to show that, on hourly time scales, afternoon rainfall that occurs over the Rocky Mountains propagates eastward onto the Great Plains but is rapidly attenuated and becomes negligible east of 100°W. This eastward rainfall propagation appears to be mediated in part by the formation of a low-level cold anomaly and increased surface pressure over the Rocky Mountains, a reversal of the upslope wind, and increased low-level zonal mass convergence over the adjacent near plains. Significance Statement Models have difficulty in simulating the diurnal time of nocturnal rainfall over the Great Plains. Deep convection in this region is often associated with severe weather. Rainfall variability over the Great Plains has a significant impact on soil moisture and agricultural productivity. This paper explores how the structure of deep convective rain events over the Great Plains varies with longitude. The results improve our understanding of deep convection development in the Great Plains and have the potential to contribute to improved forecasts of convective rainfall.

Tracking shock movement on the surface of an oscillating, straked delta wing

Limit cycle oscillations (LCO), a mechanical nonlinearity similar to flutter, have affected high performance aircraft, like the F-16 and F-18, for years. The phenomena causes a lateral motion of the cockpit that makes performance of typical pilot tasks difficult. To better understand the nature of LCO and why high performance aircraft are typically afflicted, a computational model was developed to compare to wind tunnel tests and investigate the flow field around a straked, semispan delta wing and monitor the changes as the wing was pitched in an oscillatory fashion. The oscillations were intended to mimic LCO. By understanding the flow field around an oscillating wing, the fluid force that acts as the source of the motion could be discerned. The computational investigation focused on tracking shock movement along the top surface of the wing to confirm the presence of shock-induced trailing edge separation, one possible driver of LCO. The surface pressure was shown to be sensitive to the starting trim angle, oscillation frequency and oscillation amplitude. A separation bubble aft of the shock was observed as the source of sharp, localized negative surface pressure coefficient. The large change in surface pressure caused by the separation bubble could be an important phenomena contributing to the onset of LCO.

Signatures of midsummer droughts over Central America and Mexico

The annual cycle of precipitation over most parts of Central America and southern Mexico is climatologically characterized by a robust bimodal distribution, normally termed as the midsummer drought (MSD), influencing a large range of agricultural economic and public insurances. Compared to studies focusing on mechanisms underpinning the MSD, less research has been undertaken related to its climatological signatures. This is due to a lack of generally accepted methods through which to detect and quantify the bimodal precipitation accurately. The present study focuses on characterizing the MSD climatological signatures over Central America and Mexico using daily precipitation observations between 1979 and 2017, aiming to provide a comprehensive analysis of MSD in fine scale over this region. This was completed using a new method of detection. The signatures were analyzed from three aspects, namely (1) climatological mean states and variability; (2) connections with large scale modes of climate variability (El Niño–Southern Oscillation (ENSO) and the Madden–Julian Oscillation (MJO)); and (3) the potential afforded by statistical modelling. The development of MSDs across the region is attributed to changes of surface wind–pressure composites, characterized by anomalously negative (positive) surface pressure and onshore (offshore) winds during the peak (trough) of precipitation. ENSO’s modulation of MSDs is also shown by modifying the surface wind–pressure patterns through MSD periods, inducing the intensified North Atlantic Subtropical High and associated easterlies from the Caribbean region, which induce relatively weak precipitation at corresponding time points and subsequently intensify the MSD magnitude and extend the MSD period. Building on previous research which showed MSDs tend to start/end in MJO phases 1 and 8, a fourth–order polynomial was used here to statistically model the precipitation time series during the rainy season. We show that the strength of the bimodal precipitation can be well modelled by the coefficient of the polynomial terms, and the intra-seasonal variability is largely covered by the MJO indices. Using two complete MJO cycles and the polynomial, the bimodal precipitation during the rainy season over Central America and Mexico is synoptically explained, largely contributing to our understanding of the MJO’s modulation on the MSD.

Signaling Between TRPV1/TRPV4 and Intracellular Hydrostatic Pressure in the Mouse Lens.

PurposeThe lens uses feedback to maintain zero pressure in its surface cells. Positive pressures are detected by transient receptor potential vanilloid (TRPV4), which initiates a cascade that reduces surface cell osmolarity. The first step is opening of gap junction hemichannels. One purpose of the current study was to identify the connexin(s) in the hemichannels. Negative pressures are detected by TRPV1, which initiates a cascade that increases surface osmolarity. The increase in osmolarity was initially reported to be through inhibition of Na/K ATPase activity, but a recent study reported it was through stimulation of Na/K/2Cl (NKCC) cotransport. A second purpose of this study was to reconcile these two reports.MethodsIntracellular hydrostatic pressures were measured using a microelectrode/manometer system. Lenses from TRPV1 or Cx50 null mice were studied. Specific inhibitors of Cx50 gap junction channels, NKCC, and Akt were used.ResultsEither knockout of Cx50 or blockade of Cx50 channels completely eliminated the response to positive surface pressures. Knockout of Cx50 also caused a positive drift in surface pressure. The short-term (∼20-minute) response to negative surface pressures was eliminated by blockade of NKCC, but a long-term (∼4-hour) response restored pressure to zero. Both short- and long-term responses were eliminated by knockout of TRPV1 or inhibition of Akt.ConclusionsHemichannels made from Cx50 are required for the response to positive surface pressures. Negative surface pressures first activate NKCC, but a backup system is inhibition of Na/K ATPase activity. Both responses are initiated by TRPV1 and go through PI3K/Akt before branching.

Vortex Dynamics Analysis of Straight-Body-Type-Fuselage Fighter Using CFD Simulation

The choice for using a fighter fuselage in a fighter jet design affects a vortex generation advantageous in maneuverability. To study the effect of straight-body-type-fuselage (SBTF) on the vortex dynamic, a computational fluid dynamics (CFD) method is used, in order to simulate a model of SBTF fighter. The simulation uses Q-criterion to probe vortices, and a logarithmic grid to emphasize the micro-gridding effect of the turbulent boundary layer. The results show detailed quantitative velocity, pressure, trajectory of the vortex core, and wing negative surface pressure distribution (SPD), providing clear pictures of opportunity for performance improvement, better lift, agility, and maneuverability of a fighter if a model requires a new design.

Influence of global sea‐surface temperature on ultra‐low‐frequency variability in Indian summer monsoon rainfall

AbstractA multidecadal or ultra‐low‐frequency mode of variability in Indian summer monsoon rainfall (ISMR) with a spectral peak at nearly 67 years is identified using a nonparametric approach, namely, singular spectrum analysis. Not only does this mode modulate the seasonal mean rainfall over India, but also frequent occurrences of excess or below normal rainfall over India are favored by the phases of this mode. We show that 80% of all droughts occur during the negative phase of this mode, compared with 60% of all floods during its positive phase. Although the existence of this mode was reported in many previous studies, proper understanding of its exact nature and driving mechanism, and how it relates to global sea‐surface temperature (SST), is still not clear. Here, we show that the 67‐year variability in ISMR is associated with a SST mode of similar periodicity, which primarily exhibits a hemispheric SST difference, with the strongest signals over the northern Pacific and Atlantic. The positive phase of this SST mode induces low surface pressure over the northern Arabian Sea. Changes in surface pressure over the northern Arabian Sea govern changes in ISMR. The bridge between the SST mode and central Asian circulation is possibly established through the North Pacific Oscillation. The positive phase of this mode enhances the meridional temperature gradient over India, which acts to strengthen the tropical easterly jet, and subsequently the low‐level westerly jet over India. These lead to a negative surface pressure anomaly over the Indian subcontinent and an associated anomalous cyclonic circulation. The environment thus created is conducive to increased seasonal mean monsoon rainfall over India. The phase of the SST mode is remarkably similar to, and leading by 2–3 years, that of the multidecadal mode in ISMR up to the 1990s. However, the relationship weakens after the early 1990s.

The Flow Visualization CFD Studies of the Fuselage and Rolled-up Vortex Effects of the Chengdu J-10-like Fighter Canard

Fighter aircrafts with high maneuverability and swiftness are due to fuselage effects, caused by canard-fuselage-main wing configuration. Even though the flows around fighters are highly complex, mostly they create rolled-up vortices capable to delay stalls and increase maximum lifts (Calderon, Wang & Gursul, 2012; Mitchell & Delery, 2001; Boelens, 2012; Chen, Liu, Guo & Qu, 2015). The vortex dynamics analysis method employment is introduced, in this case we focus only on the fighter canard. It characterizes the vortex core, develops the pitching moment & main wing total lift, and exploits the vortex centre visualization, the strength, negative surface pressure and its trajectory.This paper explains the influence of the fighter fuselage, it generates rolled-up vortex effects, causes the flow deflected by the fighter fuselage head, strengthen the vortex centre to become vortex core. Above the aircraft head, due to the curved contour head effect, the second vortex centers are developed makes the vortex center above the head more dynamic. Comparing with fighter without fuselage, the flow property changes, for Chengdu J-10-like model with fuselage, are concentrated at the canard leading edge, where the negative pressures are stronger, since the maximum axial velocities of the vortex centre are higher, and give more distinctive vortex breakdown locations.

Midlatitude Rossby wave modulation of the Indian summer monsoon

The dominant mode of July–August seasonal variability of Indian summer monsoon rainfall obtained by performing an empirical orthogonal function analysis over India, excluding northeast India, for the period 1979–2014 is highly correlated to the quasi‐stationary midlatitude Eurasian Rossby wave train, known as the ‘Silk Road’ pattern. A new hypothesis has been proposed and tested using observed Indian rainfall and the ERA‐Interim dataset, by which the positive feedback between the midlatitude Rossby wave and the Indian summer monsoon circulation has been established. A Rossby wave train features successive upper‐tropospheric negative and positive geopotential height anomalies over the northeast of the Mediterranean and northwest of India, respectively. The negative height anomaly decreases the sum of the vertical integral of potential and internal energy, while this increases in the region of positive geopotential height anomalies. This is associated with middle to lower tropospheric midlatitude descent and ascent anomalies at 40°E and 50°E, which cause negative surface temperature anomalies over Syria, Iraq, Jordan and Saudi Arabia, and a positive surface temperature anomaly over Iran, respectively. The negative and positive surface temperature anomalies are associated with positive and negative surface pressure anomalies over Saudi Arabia and Iran, respectively, which generate anomalous northwesterly winds over eastern Saudi Arabia and the Persian Gulf. Further downstream this anomalous northwesterly wind combines with the climatological background cross‐equatorial southwesterly flow in the Arabian Sea. The flow further converges towards central and northwest India. The flow also acts as a source of moisture supply from the warm Arabian Sea and Persian Gulf for the deep convection over the Western Ghats, northwest and central India and hence reinforces active Indian summer monsoon conditions.

Conformal symmetry wormholes and the null energy condition

In this paper we seek a relationship between the assumption of conformal symmetry and the exotic matter needed to hold a wormhole open. By starting with a Morris-Thorne wormhole having a constant energy density, it is shown that the conformal factor provides the extra degree of freedom sufficient to account for the exotic matter. The same holds for Morris-Thorne wormholes in a noncommutative-geometry setting. Applied to thin shells, there would exist a radius that results in a wormhole with positive surface density and negative surface pressure and which violates the null energy condition on the thin shell.

Feasibility of skin-friction diagnostics based on surface pressure gradient field

An intrinsic relation is given between the skin-friction vector and the surface pressure gradient through the boundary enstrophy flux (BEF), and it is used to study the possibility to extract some skin-friction structures from a surface pressure field. This attempt contains two related parts. In the first part, when the BEF field is given, a projected skin-friction field in the image plane can be sought from a surface pressure image based on a variational solution of an optical-flow-like equation. This approach is validated in several classical flows. The second part deals with a practical problem in which the BEF field is not known a priori. In this case, a so-called auxiliary skin-friction field is determined from a surface pressure image alone by using the same variational approach. The auxiliary skin-friction field has the magnitude proportional to the skin-friction magnitude and the direction of the negative surface pressure gradient. The physical meaning of the auxiliary skin-friction field and its applicability to global skin-friction diagnostics are discussed.

Impact of observed North Atlantic multidecadal variations to European summer climate: a linear baroclinic response to surface heating

The observed prominent multidecadal variations in the central to eastern (C–E) European summer temperature are closely related to the Atlantic multidecadal variability (AMV). Using the Twentieth Century Reanalysis project version 2 data for the period of 1930–2012, we present a mechanism by which the multidecadal variations in the C–E European summer temperature are associated to a linear baroclinic atmospheric response to the AMV-related surface heat flux. Our results suggest that over the north-western Atlantic, the positive heat flux anomaly triggers a surface baroclinic pressure response to diabatic heating with a negative surface pressure anomaly to the east of the heat source. Further downstream, this response induces an east-west wave-like pressure anomaly. The east-west wave-like response in the sea level pressure structure, to which we refer as North-Atlantic-European East West (NEW) mode, is independent of the summer North Atlantic Oscillation and is the principal mode of variations during summer over the Euro-Atlantic region at multidecadal time scales. The NEW mode causes warming of the C–E European region by creating an atmospheric blocking-like situation. Our findings also suggest that this NEW mode is responsible for the multidecadal variations in precipitation over the British Isles and north-western Europe.

Subseasonal variations in spatial signatures of ENSO on the Indian summer monsoon from 1901 to 2009

AbstractCorrelations of 1° by 1° seasonal rainfall with Pacific sea surface temperatures (SSTs) reveal spatially distinct teleconnections between El Niño–Southern Oscillation (ENSO) and Indian summer monsoon rainfall over the full monsoon season, as well as three subseasons. Over the full season (June–September), Pacific SSTs correlate with rainfall in Western India more than that in Eastern India. This spatial signature shifts as the monsoon progresses through early (June), middle or peak (July–August), and late (September) subseasons. Specifically, a 1°C cooling of the central equatorial Pacific (i.e., La Niña conditions) can result in the following: ∼70–100% increase in precipitation in north central Indian and the Indo‐Gangetic Plains during the early season, ∼30–80% increase peak season precipitation in south central India and northwestern Rajasthan, and ∼60–100% increase in late season precipitation in northern, northwestern, and central India. Furthermore, the spatial signatures between La Niña and El Niño are asymmetric in that for a particular location, the enhancement and suppression of rainfall associated with La Niña and El Niño conditions, respectively, are not equal. El Niño suppresses peak season rainfall in the south central and northwestern Rajasthan regions more than La Niña enhances it, but the opposite occurs during the late season in northern, northwestern, and central India. Additionally, the correspondence of minima (maxima) in anomalies of velocity potential aloft with maxima (minima) at 925 mb and with positive (negative) surface pressure anomalies suggests that anomalous subsidence (ascent) occurs in July–September during El Niño (La Niña) times. In the early season, however, patterns of velocity potential composites suggest a region of descent (ascent) over the western equatorial Indian Ocean, along with a region of ascent (descent) over the Indian subcontinent that exists only during the early season but not during the peak or late season. These patterns are consistent with the hypothesis that local Hadley cell circulation affects pressure and thus rainfall during the early season but that a larger‐scale mechanism, such as eastward or westward shifts in the Walker circulation, may be more responsible for teleconnections seen throughout the remainder of the season. These findings indicate that focusing monsoon forecasting efforts on these regions and on subseasonal periods while incorporating ENSO asymmetries will yield useful and skillful regional forecasts, compared to the declining utility and skill of all‐India summer monsoon rainfall.

A new hybrid star model in Krori-Barua spacetime

Present paper provides a new model of hybrid star with strange quark matter along with normal baryonic matter. The relation between pressure and density of the quark matter is given by the MIT bag model equation of state. The model is developed in the framework of Krori and Barua (KB) ansatz (Krori and Barua, Phys. A, Math. Gen. 8:508, 1975). All the physical requirements are satisfied by our model. The value of mass calculated from our model is close to the observational data which gives the validity of our present model. We match our interior solution to the exterior Schwarzschild metric where negative surface pressure is required to hold the thin shell against collapsing.

Using nudging to improve global-regional dynamic consistency in limited-area climate modeling: What should we nudge?

Regional climate modelling sometimes requires that the regional model be nudged towards the large-scale driving data to avoid the development of inconsistencies between them. These inconsistencies are known to produce large surface temperature and rainfall artefacts. Therefore, it is essential to maintain the synoptic circulation within the simulation domain consistent with the synoptic circulation at the domain boundaries. Nudging techniques, initially developed for data assimilation purposes, are increasingly used in regional climate modeling and offer a workaround to this issue. In this context, several questions on the “optimal” use of nudging are still open. In this study we focus on a specific question which is: What variable should we nudge? in order to maintain the consistencies between the regional model and the driving fields as much as possible. For that, a “Big Brother Experiment”, where a reference atmospheric state is known, is conducted using the weather research and forecasting (WRF) model over the Euro–Mediterranean region. A set of 22 3-month simulations is performed with different sets of nudged variables and nudging options (no nudging, indiscriminate nudging, spectral nudging) for summer and winter. The results show that nudging clearly improves the model capacity to reproduce the reference fields. However the skill scores depend on the set of variables used to nudge the regional climate simulations. Nudging the tropospheric horizontal wind is by far the key variable to nudge to simulate correctly surface temperature and wind, and rainfall. To a lesser extent, nudging tropospheric temperature also contributes to significantly improve the simulations. Indeed, nudging tropospheric wind or temperature directly impacts the simulation of the tropospheric geopotential height and thus the synoptic scale atmospheric circulation. Nudging moisture improves the precipitation but the impact on the other fields (wind and temperature) is not significant. As an immediate consequence, nudging tropospheric wind, temperature and moisture in WRF gives by far the best results with respect to the Big-Brother simulation. However, we noticed that a residual bias of the geopotential height persists due to a negative surface pressure anomaly which suggests that surface pressure is the missing quantity to nudge. Nudging the geopotential has no discernible effect. Finally, it should be noted that the proposed strategy ensures a dynamical consistency between the driving field and the simulated small-scale field but it does not ensure the best “observed” fine scale field because of the possible impact of incorrect driving large-scale field.

Singularity-free anisotropic strange quintessence star

Present paper provides a new model of anisotropic strange star corresponding to the exterior schwarzschild metric. The Einstein field equations have been solved by utilizing the Krori Barua (KB) ansatz in presence of quintessence field characterized by a parameter omegaq . The obtained solutions are free from central singularity. Our model is potentially stable.The numerical values of mass of the different strange stars SAXJ1808.4-3658(SS1)(radius=7.07 km),4U1820- 30 (radius=10 km),Vela X-12 (radius=9.99 km),PSR J 1614-2230 (radius=10.3 km) obtained from our model is very close to the observational data that confirms the validity of our proposed model. The interior solution is also matched to the exterior Schwarzschild spacetime in presence of thin shell where negative surface pressure is required to hold the thin shell against collapse.

Strange quintessence star in Krori–Barua spacetime

In the present paper a new model of a compact star is obtained by utilizing the Krori–Barua (KB) ansatz [Krori and Barua in J. Phys. A, Math. Gen. 8:508, 1975] in the presence of a quintessence field characterized by a parameter ω q with $-1<\omega_{q}<-\frac{1}{3}$ . The obtained model of strange stars is singularity free and satisfies all the physical requirements. Our model is stable as well as it is in static equilibrium. The numerical values of the mass of the strange stars 4U1820-30 (radius=10 km), SAX J1808.4-3658(SS1) (radius=7.07 km) and Her X-1 (radius=7.7 km) calculated from our model are very close to the standard data. The interior solution is matched to the exterior Schwarzschild spacetime in the presence of a thin shell where a negative surface pressure is needed to keep the thin shell from collapsing.

Evidence of negative surface pressure induced by β-lactoglobulin and β-casein at water/air interface

Protein adsorption is one of the most complex and intriguing phenomenon in interfacial science. This phenomenon has been addressed in this paper for a short time range using maximum bubble pressure tensiometer. This study presents the issue of negative surface pressure of proteins which has been much of a speculation, with the thermodynamic model. Here β-lactoglobulin has been studied at different pHs and the experimental results agree with the theoretical model presented.

On the collapse transition of a polymer brush: the case of lateral mobility.

We consider a polymer brush composed of end-grafted polymer chains. Classical theory advocates that a worsening of the solvent quality results in a smooth decrease of the brush height from a swollen to a dense brush. We report that a homogeneous brush under poor solvent conditions can have a negative surface pressure, indicating an instability in favour of lateral segregation. Also by using a two-gradient version of the self-consistent field (SCF) theory we show that, in contradiction to the classical result, but in line with the negative pressure, the collapse transition for laterally mobile chains has a first-order character, exemplified by the presence of a compact brush that coexists with a dilute gas of end-grafted chains. The dense brush assumes a pancake shape wherein the chains balance the stretching entropy against surface energies. The height of the pancake scales sub-linearly with the chain length because the local grafting density decreases with increasing chain length. In analogy with wetting studies we discuss how the spreading parameter has an influence on the pancake structure. Accordingly, the height increases with worsening of the solvent quality and decreases with increased affinity for the substrate. The two-phase state is expected in many practical situations.

Nonlinear estimation of El Niño impact on the North Atlantic winter

The differences in the teleconnections forced by different El Niño events (Niños) can be partly explained by the intrinsic nonlinearity of the atmospheric response. In the present study, we segregate the responses of the North Atlantic to strong from those to moderate Niños and compare nonlinear and linear estimates. El Niño forcing is represented by the tropical Pacific sea surface temperature anomalies, and the North Atlantic atmospheric response is represented by sea level pressure anomalies in the region. To gain insight into the evolution of El Niño teleconnections in a future climate, linear and nonlinear analyses are carried out on the corresponding data fields in the control and scenario simulations of a climate model experiment. This experiment presents, in its control version, realistic teleconnections. In the observational analysis, the nonlinear method performs only slightly better than the linear one. However, in the analysis of the interannual variability by a long control experiment of a realistic climate simulation, the nonlinear estimate improves significantly with respect to the linear one. The analysis of the corresponding scenario experiment points to an intensification of the (negative) surface pressure anomalies associated with the Niños in the west European sector in a future climate. This feature is related to the important stratospheric anomalies in the same region, revealed by previous studies.