Types Of Wave Trains Research Articles

Classification of large-scale circulation patterns and their spatio-temporal variability during High-PM10 events over the Korean Peninsula

The typical spatio-temporal evolutions of large-scale weather patterns before and after high-concentration events of particulate matter with an aerodynamic diameter ≤ 10 μm (PM10) (High-PM10) over the Korean Peninsula were investigated. Using the K-means clustering method, five significant large-scale weather patterns associated with High-PM10 events were identified. Among the 91 High-PM10 events that occurred during winter/spring of 2007–2018, approximately 41% (38 cases) belonged to Cluster 1 and 5, characterized by upper-tropospheric downstream amplification of pressure anomaly originating from the Barents/Kara Sea of the Arctic Ocean. We refer to this pattern as the wave-train type. Concurrently with this pattern, southwesterly wind anomalies from southeastern China and significant descending air occurred over the Korean Peninsula, causing PM10 accumulation. Despite its dominance of occurrence, the wave-train type exhibited a relatively shorter mean duration of 1–2 days owing to its rapid development and traveling characteristics. Cluster 2 corresponded to approximately 29% (27 cases) of the total cases, and was characterized by a stagnant anticyclone over the northeastern Eurasia region. In the lower atmosphere, southerly winds dominated the Korean Peninsula. Vertical diffusion of PM10 was restricted by a vertically stable condition in the lower-to-mid-troposphere and a notably weak wind speed. Cluster 2 had the longest duration of 3 days and the highest mean PM10 concentration compared to the other clusters. Cluster 3 corresponded to approximately 13% (12 cases) of the total cases and exhibited a stagnant anticyclone centered at the Kamchatka region. In this case, weakened westerly is observed resulting in the characteristics of a circulation pattern that easily accumulates pollutants. Cluster 4 accounted for approximately 15% (14 cases) of all cases, and is a pattern in which air of PM10 inflows following the back of the cyclone located in the northern part of the Korean Peninsula. We emphasize that most of High-PM10 events occurring over the Korean Peninsula are linked to the preceding upper-tropospheric large-scale circulation patterns. They control the low-level transports and accumulation of pollutants.

Autumn Cold Surge Paths over North China and the Associated Atmospheric Circulation

Using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model, we tracked the paths of 46 autumn cold surges affecting North China from 1961 to 2014, and classified them by clustering analysis, thereby investigating their changes and associated atmospheric circulation evolution. Our results indicate that autumn cold surges affecting North China can be classified into three types according to their paths: the north type, west type, and northwest type, with occurrences of 12, 16, and 18 respectively. Different types of cold surges have different atmospheric circulation characteristics. The north type is associated with a blocking type of atmospheric circulation pattern, with an enhanced stretching northeast ridge over the Ural Mountains and a transverse trough over Lake Baikal. However, the northwest type is characterized by a ridge–trough–ridge wave-train pattern that is located over the Barents Sea, West Siberian Plain, and Sakhalin Island, respectively. The west-type cold surge is related to a conversion type: a blocking system over the Ural Mountains forms four days before the cold surge occurrence, after which it becomes a wave-train type. The atmospheric signals detected prior to the occurrences of the three types of cold surges are also explored. The main signal of the north-path cold surges is that the energy propagates eastward from the Azores Islands to the Ural Mountains, and then forms a blocking high over the Urals. However, for the northwest-path cold surges, there is a weak trough over the Ural Mountains that gradually strengthens because the blocking high collapses over the Norwegian Sea. The key signal of the formation of the west-path cold surges is a blocking high over the Norwegian Sea’s continuous enhancement and extension to Novaya Zemlya, which results in a transmission of energy to the Ural Mountains and leads to the formation of a blocking system over here. When the above-mentioned different types of atmospheric circulation characteristics appear, the type of cold surge path and its impact area can be potentially forecasted in advance, which may reduce the losses that result from cold surges.

Prominent mode of summer surface air temperature variability and associated circulation anomalies over the Arabian Peninsula

This study investigates the dominant modes of surface air temperature (SAT) variability and associated circulation changes over the Arabian Peninsula (AP) during summer for the period 1979–2016 based on an empirical orthogonal function (EOF) analysis. The analysis results reveal that the first leading EOF mode is related to the weakening of the subtropical westerly jet stream, which may impact the AP temperature variability through the mid‐latitude Rossby wave trains (successive troughs and ridges). This can be explained by the high correlation of the AP summer temperatures with the quasi‐stationary mid‐latitude/extratropical Eurasian Rossby wave train type patterns, which influences the air temperature variability by modulating the Asian Jets. Furthermore, the high AP SAT variability is also closely associated with strong middle to lower tropospheric descent (subsidence) anomalies, which cause warm temperature anomalies over this region.

Observations of a Fast-mode Magnetosonic Wave Propagating along a Curving Coronal Loop on 2011 November 11

Abstract The detailed analysis of an interesting quasi-periodic fast-propagating (QFP) magnetosonic wave is presented using high-resolution observations taken by the Solar Dynamic Observatory. The QFP wave occurred over the west solar limb during the fast eruption phase of a nearby prominence. It propagated along a group of curving coronal loop and manifested two types of wave trains that showed different morphologies and propagation characteristics. The wavefronts of the first type wave trains are relatively broad, and they changed their propagation direction when they pass through the turning part of the guiding loop. On the contrary, the wavefronts of the other type wave trains are narrow, and their propagation did not affected by geometric changes of the guiding loop. Measurements indicate that the average speeds of the broad (narrow) wave trains is , and the period of the wave trains ranges from 54 to 458 s. We propose that the narrow wave trains may manifest the leakage of the wave trains from the guiding coronal loop, or were guided by another group of invisible coronal loop. In addition, the projection effect and weak magnetic field strength of the guiding coronal loop are proposed to explain the slow wave speed.

A new dynamical index for classification of cold surge types over East Asia

The cold surges over East Asia can be classified into wave-train type and blocking type according to their dynamic origins. In the present study, two dynamic indices are proposed to objectively identify cold surge types using potential temperature (θ) on the dynamic tropopause at 2-potential vorticity units (2-PVU) surface. The two indices are designed to represent primary characteristics of the two types of cold surge. The wave-train index (WI) is defined as a difference of anomalous θ on the 2-PVU surface between the western North Pacific and northeast China, which captures a southward (northward) intrusion of cold (warm) air mass related to the trough-ridge pattern. The blocking index (BI) is defined as a difference of anomalous θ between the subarctic region and northeast China, which indicates air mass overturning related to a reversal of the usual meridional θ gradient commonly observed in the occurrence of blocking type cold surge. Composite analyses based on the distribution of the WI and BI clearly demonstrate the dynamic evolutions of corresponding cold surge types. The wave-train cold surge is associated with a southeastward expansion of the Siberian High and northerly wind near surface, which is caused by growing baroclinic waves. During the blocking cold surge, a geopotential height dipole indicating the subarctic blocking and deepening of East Asian coastal trough induces a southward expansion of the Siberian High and northeasterly wind. Compared to the wave-train type, the blocking cold surge exhibits a longer duration and stronger intensity. In the new framework of these dynamic indices, we can detect a third type of cold surge when both the wave-train and the blocking occur together. In addition, we can exclude the events that do not have the essential features of the upper tropospheric disturbances or the subarctic anticyclonic circulation, which are responsible for cold surge occurrence, using the new indices.

A synoptic and dynamical characterization of wave-train and blocking cold surge over East Asia

Through an agglomerative hierarchical clustering method, cold surges over East Asia are classified into two distinct types based on the spatial pattern of the geopotential height anomalies at 300 hPa. One is the wave-train type that is associated with developing large-scale waves across the Eurasian continent. The other is the blocking type whose occurrence accompanies subarctic blocking. During the wave-train cold surge, growing baroclinic waves induce a southeastward expansion of the Siberian High and strong northerly winds over East Asia. Blocking cold surge, on the other hand, is associated with a southward expansion of the Siberian High and northeasterly winds inherent to a height dipole consisting of the subarctic blocking and the East Asian coastal trough. The blocking cold surge tends to be more intense and last longer compared to the wave-train type. The wave-train cold surge is associated with the formation of a negative upper tropospheric height anomaly southeast of Greenland approximately 12 days before the surge occurrence. Further analysis of isentropic potential vorticity reveals that this height anomaly could originate from the lower stratosphere over the North Atlantic. Cold surge of the blocking type occurs with an amplifying positive geopotential and a negative potential vorticity anomaly over the Arctic and the northern Eurasia in stratosphere. These anomalies resemble the stratospheric signature of a negative phase of the Arctic Oscillation. This stratospheric feature is further demonstrated by the observation that the blocking type cold surge occurs more often when the Arctic Oscillation is in its negative phase.

Relationship between the Arctic Oscillation and Cold Surges over East Asia

Abstract The present study reveals the changes in the characteristics of cold surges over East Asia associated with the Arctic Oscillation (AO). Based on circulation features, cold surges are grouped into two general types: wave train and blocking types. The blocking type of cold surge tends to occur during negative AO periods, that is, the AO-related polarity of the blocking type. However, the wave train type is observed during both positive and negative AO periods, although the wave train features associated with negative AO are relatively weaker. The cold surges during negative AO are stronger than those during positive AO in terms of both amplitude and duration. The cold surges during positive AO in which the extent of effect is confined to inland China passes through East Asia quickly because of weaker Siberian high and Aleutian low, leading to short duration of these cold surges. In contrast, the cold surge during negative AO, characterized by a well-organized anticyclone–cyclone couplet with high pressure over continental East Asia and low pressure over Japan, brings continuous cold air into the entire East Asian region for more than one week with long-lasting cold advection. It is also found that the tracks of the cold surges during negative AO tend to occur more frequently over Korea and Japan and less frequently over China, compared with those during positive AO. The tracks are related to a west–east dipole structure of the ratio of rain conversion to snow according to AO phase, resulting in freezing precipitation or snowfall events over inland China (Korea and Japan) are likely to occur more frequently during the positive (negative) AO periods.

Influences of Arctic Oscillation and Madden‐Julian Oscillation on cold surges and heavy snowfalls over Korea: A case study for the winter of 2009–2010

In the winter of 2009–2010, frequent and long‐lasting cold weather affected Korea. Four major cold surges and several heavy snowfall events were observed, including a record‐breaking event on 4 January 2010. These four cold surges had distinct properties with regard to their relationships to the phases of the Arctic Oscillation (AO) and the Madden‐Julian Oscillation (MJO), suggesting the possible influences of the AO and MJO on the cold surges and heavy snowfalls. The four cold surges were of two distinct types: the wave train type and the blocking type, which were differentiated by their mechanisms. With regard to the relationships of the cold surges to the AO, three cold surges occurred during a strongly negative AO period, which lasted for more than 1 month. The Siberian High expanded from the Arctic high‐pressure region to East Asia during the negative AO period. A cold surge occurred during a positive AO, with the expansion of the Siberian High across the Eurasian continent. An MJO‐induced circulation, corresponding to strong tropical convection over the tropical Indian Ocean, seems to have reinforced the cold surges over East Asia. In addition, the active local Hadley circulation modulated by a convection center over the Indian Ocean tends to enhance midlatitude synoptic disturbances across East Asia and provides favorable conditions for upward motion over the region. In short, the effects of the AO and MJO, along with the existing low‐level moisture supply, contributed to heavy snowfalls associated with strong cold surges over Korea during the winter of 2009–2010.

Compaction in a mantle with a very small melt concentration: Implications for the generation of carbonatitic and carbonate-bearing high alkaline mafic melt impregnations

Xenoliths entrained in alkaline basalts and kimberlites give strong evidence that mantle carbonatitic and carbonated high alkaline mafic silicate melts, which are initially produced at very low degrees of partial melting (≪1%), percolate and accumulate to form impregnations with a melt concentration of up to 10%. At present no compaction model has explained such huge local amplification of melt concentration. Recently, Bercovici et al. [1] have shown that the commonly used equations of compaction are not sufficiently general to describe all melt percolation processes in the mantle. In particular, they show that, when the melt concentration in the mantle is very low, the pressure jump ΔP between the solid and liquid fractions of the mantle mush is very important and plays a driving role during compaction. 1-D compaction waves generated with two different systems of equations are computed. Three types of wave-trains are observed, i.e. (1) sinusoidal waves; (2) periodic waves with flat minima and very acute maxima (‘witch hat waves’); (3) periodic solitary waves with flat maxima and extremely narrow minima (‘bowler hat waves’). When the initial melt distribution in the mantle is quite homogeneous, the compaction waves have sinusoidal shapes and can locally amplify the melt concentration by a factor less than two. When there is a drastic obstruction at the top of the wetted domain, the pressure jump ΔP between solid and liquid controls the shape of the waves. If the computation assumes the equality of pressure between the two phases (ΔP=0), the compaction wave has a ‘bowler hat shape’, and locally amplifies the melt concentration by a factor less than 5. Alternatively, simulations taking into account the pressure jump between phases ΔP predict compaction waves with ‘witch hat shape’. These waves collect a large quantity of melt promoting the development of magmons with local melt concentration exceeding 100× the background melt concentration. It is inferred that in a mantle with very low concentrations of carbonatitic or high alkaline mafic silicate melt the magmons are about 1 km thick and reach, in less than 1 Ma, a melt concentration of about 10%. The magmons are likely generated below the lithosphere at some distance away from the center of hot spots. This can explain the development of mantle carbonatitic eruptions in the African rift and the carbonatite and high alkaline mafic silicate volcanic activity in oceanic islands.

NONLINEAR OPTICS IN THE NEAR-FIELD ZONE OF ATOMS

Elements of a new quantum electrodynamic theory which might enable one to obtain a better understanding of the linear and nonlinear interaction between atomic systems in near-field contact is presented. To follow the space-time dynamics in the atomic near-field zone an electromagnetic propagator formalism with polychromatic photons is constructed. A first-quantized description based on the photon energy wave function for free polychromatic photons is extended in such a manner that the birth process of the photon, which takes place in the near-field zone of the source, can be followed. In order to be able to describe harmonic generation processes in near-field optics polychromatic photons of the simple wave-train type are used. The wave mechanical (first-quantized) description based on wave-train photons is upgraded to a field-theoretic (second-quantized) formalism using a new so-called propagator gauge which is closely related to the Poincaré gauge underlying the multipole description of quantum electrodynamics.

Excitation of 3D-disturbances in wall-bounded shear flow with adverse pressure gradient

The excitation of 3D disturbances by a time-harmonic Dirac point source at the wall in a decclerated and a flat-plate boundary layer is compared. It is demonstrated that the linearized parallelflow theory including the receptivity problem can capture the main features of unstable 3D wavetrains found in previous experiments. Depending on the exciting frequency, three different types of wavetrains are identified.

Solitary wave trains in a cold plasma

The existence of traveling solitary waves, the products of modulation instability in a cold quasi-neutral plasma, is considered. Solitary waves of this type (“solitary wave trains”) are formed as a result of bifurcation from a nonzero wave number of the linear wave spectrum. It is shown that the complete system of equations describing the wave process in a cold plasma has solutions of the solitary wave train type, at least when the undisturbed magnetic field is perpendicular to the wave front. Sufficient conditions of existence of solitary wave trains in weakly dispersive media are also formulated.

A SURVEY OF "RANDOM" WAVE GENERATION TECHNIQUES

Techniques of producing waves in hydraulic models and laboratory flumes have evolved from the simple electrical-mechanical technique of some 15 years ago, to the present sophisticated hydraulic-electric servo systems, controlled by on-line computers and capable of producing a large number of different types of sea states. An accurate definition of the required sea state has become very important, since it has been shown that different types of wave trains, although all having the same significant wave heights and periods, can produce large differences in the results of model tests. Even a specification of the input spectrum, including all relevant spectral parameters, is not sufficient. The occurrance of wave groups, for instance, has to be defined separately. Table 1 illustrates which sea state parameters (A-E) need to be defined and controlled in the laboratory for different types of model studies (1-9). This is just shown as an example, and does not pretend to be a definitive statement. There exists presently a great variety of different techniques and methods to produce irregular waves and there is no assurance that testing the same model in different laboratories will give similar results. As a first step to address this problem, it was thought to be useful to determine the variety (or perhaps similarity) of all laboratory wave generation systems presently used. A discussion with representatives of a number of hydraulics laboratories and ship towing tanks in the spring of 1979 led to the organisation of a survey of wave generation and analysis systems. The results of the survey are shown in the same format as the questionnaire. A list of all institutes which participated is also included.

Nonlinear magnetosonic waves propagating perpendicular to a magnetic neutral sheet

Nonlinear magnetosonic waves propagating in a magnetic neutral sheet are investigated within the framework of a fluid model. It is shown that the behavior of the magnetosonic waves is governed by a ‘modified Burgers equation’ with an additional termc(η)ϕ due to the relevant slowly varying background plasma parameter (density or magnetic field), $$\frac{{\partial \phi }}{{\partial \eta }}$$ where ϕ(ξ, η) is the amplitude of the wave,\(\xi = \int {k_x } {\text{d}}x + k_y y - \omega t\), and η=ex is the coordinate stretched by a smallness parameter e. When we consider fast magnetosonic waves propagating toward the neutral region across the magnetic field, they grow and undergo rapid steepening after passing through the neutral region; i.e., shock formation is promoted by the background inhomogeneity. By the numerical computation of the above equation, the time evolution is examined for two initial disturbances, the pulse type (gaussian) and the wave train type (sinusoidal wave).