Role Of Wind Shear Research Articles

The possible effect of turbopause on formation of mid-latitude sporadic E layers

Sporadic E (Es) layers are thin enhanced ionization patches. The electron density of Es layer is very high, up to 100 times that of the regular E layer. Therefore, Es layer has a significant effect on radio wave propagation. The formation mechanisms of Es layers is very complicated, so it needs multi-observations and simulations research. Combined observations using an ionosonde, very high frequency (VHF) coherent backscatter radar, VHF broadband backscatter radar, and meteor radar were performed. The height and irregular structure of mid-latitude Es layers observed by ionosonde, VHF coherent backscatter radar and VHF broadband backscatter radar were compared with the zonal and meridional winds observed by meteor radar, the role of wind shear on the formation of Es layer was confirmed, and examples were also found where wind shear theory could not explain and apply to the formation of Es layer. We simulated the formation of Es layers based on wind shear theory. The results of simulations and observations revealed other potential role for Es layer formation besides wind shear. By comparing the height of turbopause with that of Es layer, it was found that the variation of the altitudes of turbopause and Es layer was consistent over different latitude stations, and the effect of the turbopause on the formation of Es layer was proposed. The combined effects of eddy diffusion below and molecular ion collision above turbopause can prevent metal ions from drifting downward and promote their convergence to form thin plasma layers at the turbopause height. The turbopause accumulation effect is considered as a potentially important mechanism for the formation of Es layers besides wind shear theory. The study in the paper is helpful for analysis of physical origin and modeling of Es layer.

Role of Wind Shear in the Decay of Convective Boundary Layers

The role of wind shear in the decay of the convective boundary layer (CBL) is systematically investigated using a series of large-eddy simulations. Nine CBLs with weak, intermediate, and strong wind shear are simulated, and their decays after stopping surface heat flux are investigated. After the surface heat flux is stopped, the boundary-layer-averaged turbulent kinetic energy (TKE) stays constant for almost one convective time scale and then decreases following a power law. While the decrease persists until the end of the simulation in the buoyancy-dominated (weak-shear) cases, the TKE in the other cases decreases slowly or even increases to a level which can be maintained by wind shear. In the buoyancy-dominated cases, convective cells occur, and they decay and oscillate over time. The oscillation of vertical velocity is not distinct in the other cases, possibly because wind shear disturbs the reversal of vertical circulations. The oscillations are detected again in the profiles of vertical turbulent heat flux in the buoyancy-dominated cases. In the strong-shear cases, mechanical turbulent eddies are generated, which transport heat downward in the lower boundary layers when convective turbulence decays significantly. The time series of vertical velocity skewness demonstrates the shear-dependent flow characteristics of decaying CBLs.

Role of wind shear, temperature lapse rate, and aerosol in assessment of atmospheric condition

The near-surface environment of the earth remains either in calm or in a turbulent state as per the kinetic force acts, which encourage the growth of disturbance in the atmospheric fluid. In a stable condition, mixing of the air particles at different heights reduces the overall vertical variability of the air particles in the atmosphere while unstable atmospheric condition produces the minimum shear that leads to convective situation and promotes the mixing of its composition. To analyse these types of atmospheric conditions, here two basic parameters temperature lapse rate and aerosol optical depth (AOD), has been taken into consideration. Along with these parameters, a model named hybrid single particle lagrangian integrated trajectory (HYSPLIT) has been utilised to track the air parcel or wind flow pattern. The observations were made over Guwahati (26°N, 92°E), NE region of India. It has been determined from the observations that the wind shear (WS) follows a seasonal pattern. On certain days, the shear is higher than that of the normal condition. In this context, parameters temperature lapse rate and AOD along with WS has been observed and examined to analyse the stability of the atmosphere. It is observed that on the day of high WS value, high AOD and slow decrease of temperature per km (vertically with height) shows a completely different pattern than the normal one.

Structures in sporadic‐E observed with an impedance probe during the SEEK Campaign: Comparisons with neutral‐wind and radar‐echo observations

In order to clarify the origin of the so‐called quasi periodic echoes (QPE) that have been often detected by radar observations in the presence of sporadic‐E (Es) layers in the nighttime midlatitude ionosphere, two sounding rockets were launched during the SEEK (Sporadic‐E Experiment over Kyushu) campaign. Each rocket carried a swept‐frequency impedance probe to measure the E‐region electron‐density (Ne) profile. Using the four Ne profiles obtained during the two rocket flights together with a neutral‐wind profile obtained from a trimethyl aluminum (TMA) chemical release experiment on one of the rockets and QPE obtained with a ground‐based radar, we consider the role of wind shear in the formation of the observed Es layers, and the question of whether QPE are associated with Es layers that are modulated in altitude. The Ne profiles of Es structures that were obtained in the presence of QPE were characterized by the highly concentrated thin layers. The formation of such a thin layer by a neutral‐wind shear process was confirmed in comparison with the TMA measurements. The peak Ne values of the Es layers ranged from 2.2 to 9.3 × 104 el/cm³ near 100‐km altitude. These primary Es layers were accompanied by significant secondary structures that were located about 12 to 20 km above the main Es layers and had peak Ne that ranged from 5.2 × 10³ to 1.3×104 el/cm³. The average altitude profiles of QPE approximately covered the range where the Es‐layer peaks appeared. Our principal finding is that the observed Es structures tended to resemble horizontally stratified layers rather than structures with deep altitude modulation like previous QPE model, although the rocket measurements were separated from those by radar by 90 to 145 km.