Characteristics of Soliton with Dynamic Constraints on its Existence/Propagation in Tropical Easterly Wave

The study concerns the propagation of easterly wave (EW) at tropics as west-moving soliton more steady both in ionn and velocity as evidenced in the dynamic framework.Under the impact of different circulation patterns over the regions of western Pacific trade wind,South-Asia monsoon and their transition,such a soliton becomes tapering off during its westward movement and degrading to a common dispersive wave on the whole,followed by dismtegra-non when striking the South-China Sea monsoon segment,thereby indicating that the sea sector is inaccessible to the soliton When no monsoon trough is present over the South Asian monsoon area around 30癗 or the monsoon depression ]S shallow,it is likely to have west-travelling soliton,which suggests the incursion of the EW into the South-Asian monsoon region.

Cause Analysis of a Double-cyclone Type of Rainstorm Process with Easterly Wave

On the basis of comprehensive analysis on weather background and main influencing system of rainstorm formation,using NCEP reanalysis data,rainfall data of Shaoyang ground regional automatic station,a new generation of Doppler weather radar product information,etc.,high-altitude weather situation and physical formation mechanism of local double-cyclone type of rainstorm process with easterly wave in Shaoyang area on August 14,2016 were analyzed in detail,to find out prophase signal features which had indicating significance for rainstorm forecast. The results showed that:(1) the position of zonal subtropical high pressure in east-west direction was the necessary condition for the formation of easterly wave.(2) The rainstorm formation was closely related to double tropical depressions acting in the south of subtropical high pressure,and westward movement of easterly wave over 500 hPa and low-pressure inverted trough at low layer were main impact systems of the rainstorm.(3) Continuous flow of water vapor from the South China Sea to northwest was the source of water vapor required by this rainstorm.(4) Numerical prediction model products had certain guiding significance for forecasting the heavy precipitation,with important reference value.(5) Doppler radar products had strong forecasting ability in the nowcasting of rainstorm falling zone,which was an important measure of correcting forecast errors.

Analysis on an Easterly Wave Thunderstorm and Gale Weather during the Latter Flood Season of 2010

[Objective] The research aimed to analyze an easterly wave thunderstorm and gale weather during the latter flood season of 2010.[Method] Based on conventional observation data,data of automatic station,NCEP 1°×1° reanalysis data,Doppler radar reflectivity and radial velocity data,the easterly wave thunderstorm and gale weather process which happened during 4-5 August,2010 was analyzed.The circulation situation,wind field and dynamic & thermal structures of easterly wave,echo characteristics of Doppler radar when thunderstorm and gale happened were studied.[Result] The thunderstorm and gale weather happened in the northeaster zone in front of the deep thick easterly wave trough.When thunderstorm and gale weather happened,position of the subtropical high was by north(ridge line was at 35° N).Eastward movement of the north branch of trough compelled subtropical high splitting into east and west circles.Westward extension of the east subtropical high and saddle-type field circulation were favorable for generation and development of the easterly wave.As development and westward movement of the easterly wave,in the influence zone in front of the trough,upper easterly component transmitted downward.Then,low-level northeaster obviously strengthened,and thunderstorm and gale weather appeared.In the zone where thunderstorm and gale happened,airflow had cyclonic convergence at the middle and low layers and anti-cyclonic divergence near the ground layer.Subsidence movement was obvious.Moreover,thermal force structure that it tended to be dry and cold at the middle and high layers,warm and wet at the low layer existed.Supercell storm was at the developed stage on 4th.It had obvious mesocyclone and hooked echo characteristics(meso-and small-scale characteristics).Characteristics of the squall line,gale region and adverse wind region appeared in central west Guangdong on 5th.Doppler characteristics of the mesocyclone,hooked echo,squall line,gale region and adverse wind region had indication significance for short-imminent forecast of the thunderstorm and gale.[Conclusion] This research revealed some information which had significance for forecasting local easterly wave thunderstorm and gale weather.

An Easterly Wave Generated Heavy Rainfall Event over South India—A Case Study

Easterly waves are one of the rain-bearing systems of northeast monsoon and produce massive rainfall events over south India. In the present case study, an attempt is made to identify extreme heavy rainfall event over south India on 26th October, 2006 due to the passage of the easterly wave. Satellite images provide an inverted v-shape easterly wave. Next, circulation features at different levels clearly indicate the location, movement and speed of the easterly wave. Strong north-easterlies with a magnitude of 9.9 m/s are maintained at the surface. The convergence is mainly occupied between 12°N - 16°N, while the divergence is 5°N - 12°N on 26th October, 2006 at the surface level. On 25th, easterly wave is advected north of trough with a magnitude of 0.2 m/s and increased during the remaining days. There are two divergence cells along 5°N and 16°N before and after the event at 700 hPa level. Thus this study helps to bring out the essential characteristics of the easterly wave during northeast monsoon. The highlight of this study is that the easterly wave creates floods in the absence of tropical cyclones over south India.

Mean Kinematic Characteristics of Synoptic Easterly Disturbances over the Atlantic

This study investigates the mean kinematic characteristics of the tropical Atlantic easterly disturbances in January-March （JFM）, April-June （AM J）, July-September （JAS） and October-December （OND） from 1968-1998. For each season, the preferential tracks of these disturbances in the 3--10-day band periods were computed and spatialized, as well as their associated wavelength, velocity and main period, which lies between 3-5 days and between 6-9 days depending on the track and the season. Two main tracks are highlighted over the Atlantic Ocean. During OND and JFM these two tracks are well separated and located in each hemisphere around 15°S and 12.5°N. From AMJ to JAS these tracks migrate northward; in JAS, they merge into one over the northern tropical Atlantic along 17.5°N. The associated wavelength fields exhibit a meridional gradient, with large wavelengths （greater than 4000 km） around the equator, between 5°N and 5°S, and smaller wavelengths outside of this latitude band （between 2500-3500 kin）. The phase speed is also found to exhibit poleward decreasing values from 12-6 m s^-1. Over the north Atlantic track, 6-9-day disturbances were found to occur from January to May and approximately from October to December. From June to September, the 3-5-day waves dominate the synoptic activity. Over the south Atlantic track, between May and August the synoptic variability is mainly explained by the 3-5-day disturbances but from January to April and from September to December both 3-5-day waves and 6-9-day waves can occur.

Application of SWAN+ADCIRC to tide-surge and wave simulation in Gulf of Maine during Patriot's Day storm

The southern coast of the Gulf of Maine in the United States is prone to flooding caused by nor＇easters. A state-of-the-art fully-coupled model, the Simulating WAves Nearshore （SWAN） model with unstructured grids and the ADvanced CIRCulation （ADCIRC） model, was used to study the hydrodynamic response in the Gulf of Maine during the Patriot＇s Day storm of 2007, a notable example of nor＇easters in this area. The model predictions agree well with the observed tide-surges and waves during this storm event. Waves and circulation in the Gulf of Maine were analyzed. The Georges Bank plays an important role in dissipating wave energy through the bottom friction when waves propagate over the bank from offshore to the inner gulf due to its shallow bathymetry. Wave energy dissipation results in decreasing significant wave height （SWH） in the cross-bank direction and wave radiation stress gradient, which in turn induces changes in currents. While the tidal currents are dominant over the Georges Bank and in the Bay of Fundy, the residual currents generated by the meteorological forcing and waves are significant over the Georges Bank and in the coastal area and can reach 0.3 m/s and 0.2 m/s, respectively. In the vicinity of the coast, the longshore current generated by the surface wind stress and wave radiation stress acting parallel to the coastline is inversely proportional to the water depth and will eventually be limited by the bottom friction. The storm surge level reaches 0.8 m along the western periphery of the Gulf of Maine while the wave set-up due to radiation stress variation reaches 0.2 m. Therefore, it is significant to coastal flooding.

Diagnosis of a Severe Rainstorm Event Induced by Eastly Wave and Vortex in Off Southeast Coast of China

Using the NCEP reanalysis at 1°×1° resolution in conjunction with satellite imagery,a study is undertaken of easterly wave related rainstorm events on August 3~4,2001 in seaboards between northern Fujian and southern Zhejiang,expounding the scheme for computing helicity,and exploring the rainstorm evolution and the genesis of the Yandang mountains-triggered a meso-vortex(Duan and Chen,2005) by means of helicity and Q vector divergence.Besides,MM5V2 is employed to simulate the easterly wave caused meso-vorte...

Analysis of Rainstorm Process in South China from September 7 to 8, 2022

Based on the NCEP data of the United States, a rainstorm process in South China during September 7 to 8, 2022 was studied. Synoptic method is a qualitative and empirical forecasting method. The results show that: In early September 2022, the cold air behind the trough line from northeast China to North China can directly drive southward and invade South China from the east road. Typhoon Hinnamnor is located in the saddle field between the mainland subtropical high and the offshore subtropical high. It moves northward on the west side of the coastal subtropical high, affecting the Taiwan Island and the coastal areas of East China. During September 7-8, the wave trough of the 925 hPa Easterly wave was located near 110°E. Easterly jet existed in the southeast of South China. The center of the easterly jet was located to the east of Hainan Island, which could transport abundant water vapor from the sea surface to the sky over South China. The precipitable water in the whole layer of the atmosphere decreased from the southern coastal areas to the north, reaching more than 50 mm in southern China, of which most of the South China Sea, Hainan Island and parts of the western part of Guangdong Province exceeded 60 mm, providing sufficient water vapor supply. The circulation field with convergence at low level and divergence at high level is conducive to vertical uplift to form precipitation.

On the two-layer high-level Green-Naghdi model in a general form

The traditional high-level Green-Naghdi(HLGN)model,which uses the polynomial as the shape function to approximate the variation of the horizontal-and vertical-velocity components along the vertical direction for each-fluid layer,can accurately describe the large-amplitude internal waves in a two-layer system for the shallow configuration(h_(2)/λ■1,h_(1)/λ■1).However,for the cases of the deep configuration(h_(2)/λ■1,h_(1)/λ=O(1)),higher-order polynomial is needed to approximate the variation of the velocity components along the vertical direction for the lower-fluid layer.This,however,introduces additional unknowns,leading to a significant increase in computational time.This paper,for the first time,derives a general form of the HLGN model for a two-layer fluid system,where the general form of the shape function is used during the derivation.After obtaining the general form of the two-layer HLGN equations,corresponding solutions can be obtained by determining the reasonable shape function.Large-amplitude internal solitary waves in a deep configuration are studied by use of two different HLGN models.Comparison of the two HLGN models shows that the polynomial as the shape function for the upper-fluid layer and the production of exponential and polynomial as the shape function for the lower-fluid layer is a good choice.By comparing with Euler’s solutions and the laboratory measurements,the accuracy of the two-layer HLGN model is verified.

Experiments and calculations of wave breaking and evolution of wave groups with high steepness

The evolution of the nonlinear wave groups in deep water is investigated through laboratory measurements and numerical analysis.Laboratory experiments are conducted in deep-water wave tank,focusing on the characteristics of breaking waves arising from the evolved wave train.Some quantitative results are obtained for the significant breaking wave train,including the surface elevation time series,the local geometry,and the energy dissipation.A nonlinear model for the evolution of the wave groups in deep water is developed by adding eddy viscosity dissipation terms in the High Level Irrotational Green-Naghdi(HLIGN)equations.The results of the simulation are compared with the laboratory measurements,and good agreement is observed for the evolved wave train.

Dynamical effect of the zonal wind anomalies over the tropical western Pacific on ENSO cycles

The circulation and zonal wind anomalies in the lower troposphere over the equatorial western Pacific and their roles in the developing and decaying processes of the 1982–1983, 1986 –1987, 1991–1992 and 1997–1998 El Ni?o events and the occurrence of La Ni?a events are analyzed by using the observed data in this paper. The results show that before the developing stage of these El Ni?o events, there were cyclonic circulation anomalies in the lower troposphere over the tropical western Pacific, and the anomalies brought the westerly anomalies over the Indonesia and the tropical western Pacific. However, when the El Ni?o events developed to their mature phase, there were anticyclonic circulation anomalies in the lower troposphere over the tropical western Pacific, and the anomalies made the easterly anomalies appear over the tropical western Pacific. A simple, dynamical model of tropical ocean is used to calculate the response of the equatorial oceanic waves to the observed anomalies of wind stress near the sea surface of the equatorial Pacific during the 1997/98 ENSO cycle, which was the strongest one in the 20th century. It is shown that the zonal wind stress anomalies have an important dynamical effect on the devel-opment and decay of this El Ni?o event and the occurrence of the following La Ni?a event.