Altitude and intensity characteristics of parametric instability excited by an HF pump wave near the fifth electron harmonic

An ionospheric heating experiment involving an O mode pump wave was carried out at European Incoherent Scatter Scientific Association site in Troms？. The observation of the ultra high frequency radar illustrates the systematic variations of the enhanced ion line and plasma line in altitude and intensity as a function of the pump frequency. The analysis shows that those altitude variations are due to the thermal effect, and the intensity variations of the enhanced ion line are dependent on whether or not the enhanced ion acoustic wave satisfy the Bragg condition of radar. Moreover, a prediction that if the enhancement in electron temperature is suppressed,those systematic variations will be absent, is given.

An evaluation of input/dissipation terms in WAVEWATCH Ⅲ using in situ and satellite significant wave height data in the South China Sea

A WAVEWATCH III version 3.14（WW3） wave model is used to evaluate input/dissipation source term packages WAM3, WAM4 and TC96 considering the effect of atmospheric instability. The comparisons of a significant wave height acquired from the model with different packages have been performed based on wave observation radar and HY-2 altimetry significant wave height data through five experiments in the South China Sea domain spanning latitudes of 0°–35°N and longitudes of 100°–135°E. The sensitivity of the wind speed correction parameter in the TC96 package also has been analyzed. From the results, the model is unable to dissipate the wave energy efficiently during a swell propagation with either source packages. It is found that TC96 formulation with the ＂effective wind speed＂ strategy performs better than WAM3 and WAM4 formulations. The wind speed correction parameter in the TC96 source package is very sensitive and needs to be calibrated and selected before the WW3 model can be applied to a specific region.

Hundred-watt level all-fiber visible supercontinuum generation from a graded-index multimode fiber

A monolithic visible supercontinuum(SC)source with a record average output power of 204 W and a spectrum ranging from580 nm to beyond 2400 nm is achieved in a piece of standard telecom graded-index multimode fiber(GRIN MMF)by designing the pumping system.The influence of the GRIN MMF length on the geometrical parameter instability(GPI)effect is analyzed for the first time,to the best of our knowledge,by comparing the SC spectral region dominated by the GPI effect under different fiber lengths.Our work could pave the way for robust,cost-effective,and high-power visible SC sources.

Capital flows, economic growth and the real effective exchange rate: Evidence from China

This paper examines the Granger causal relationship between capital flows and economic growth in China over the period 1998Q1–2019Q2,allowing for real effective exchange rate(REER)effects.As parameter instability tests indicate structural changes,we use bootstrap rolling window causality tests,which suggest that the causal nexus between capital flows and GDP growth is time-varying.We find that the causal links between foreign direct investments(FDIs)and GDP growth are hardly affected by the REER,whereas the REER plays a more important role in affecting the causal connections between portfolio investments and other investments and GDP growth.Our results suggest that cumulative portfolio inflows and cumulative other investment inflows harm GDP growth,whereas cumulative portfolio outflows and cumula-tive other investment outflows positively affect GDP growth.

Simulation Study About the Influence of Atmospheric Stratification on Lightning Activities

A 2D model about charging and discharging processes in thundercloud is used to simulate three differential atmospheric stratifications resulting in discrepant thunderstorm processes in Beijing region. The dynamic and microphysical processes in thunderstorm and their influence on lightning activities are also discussed. The results indicate that ascending velocity and water vapor are the most important factors to influence lightning activities. At the same time, they affect each other and are together controlled by atmospheric stratification. The magnitude of the ascending velocity determines the intensity of storm and the time when the thunderstorm matured. The thunderstorm with strong updrafts can reach a large height in a short time. Strong persistent updrafts and sufficient water vapor which help to generate more ice phase hydrometeors that directly influence charging and discharging process will prolong the mature stage of the thunderstorm and thereby enhance lightning activities. Though the big density of ice phase hydrometeors can be formed, it is difficult to sustain a long time in the condition of strong updrafts and scant water vapor. Under the condition of weak updrafts and sufficient water vapor in the whole levels, it is easy to form warm cloud process in which the ice phase process and lightning activities are weak. The favorable stratification conditions for strong lightning activities are the sufficient vapor in the lower atmosphere, moderate humidity in the mid troposphere. big instability energy and some suitable convective inhibition. Through calculating some atmospheric instability parameters, it is indicated that convective instability index smaller than -10℃ （negative means instable）, convective available potential energy larger than 1000 J kg-1, convective inhibition larger than 40 J kg-1 the 700-hPa potential equivalent temperature larger than 340 K and the 35%-85% humidity in the mid troposphere （700-400 hPa） are the advantageous conditions for strong lightning activities.

Increasing Trend of Summertime Synoptic Wave Train Activity over the Western North Pacific since 1950

The change of summertime synoptic-scale wave train(SWT) activity over the western North Pacific(WNP) since1950 was investigated based on the NCEP–NCAR reanalysis data. It is found that the intensity of SWT has a rising trend, while its structure and phase propagation characteristics remain unchanged. Environmental factors responsible for the rising trend are investigated. By separating the whole period into three warming phases(P1: 1950–1958, P2:1978–1986, and P3: 2006–2014), we found that even though the vertical velocity shows a rising trend, the background low-level vorticity over the monsoon trough region increases from P1 to P2 but decreases from P2 to P3, and so is the low-level barotropic energy conversion(CK). Thus, just the environmental dynamic factor could not explain the continuous rising SWT trend. On the other hand, thermodynamic factor, such as the sea surface temperature(SST), moisture, and atmospheric instability, shows a clear step-by-step increasing trend. A non-dimensional synoptic activity index(SAI) that combines the dynamic and thermodynamic factors is then proposed. This index well captures the observed long-term trend of the SWT intensity.