Breaks in monsoon and related precursors

A comprehensive analysis of eleven break monsoon situations that occurred during the period 1987 to 1997 have been attempted in the study. The various features like daily rainfall departures, wind anomalies and the satellite derived Outgoing Long wave Radiation (OLR) associated with the commencement/cessation of the break monsoon condition are studied with a view to identifying the precursors associate the break situation. The results reveal that there is progressive decrease of below normal rainfall departures 5 days prior to the actual break day in the latitude belts south of 20° N. During the period of the revival of the monsoon, the time section of the daily rainfall departures shows that the daily rainfall departure first starts becoming above normal in the southern most latitudinal belt 5° N to 10°N from the second day onwards after the cessation of the break. Similarly, the easterly anomalies in the zonal wind are first noticed in the southern latitude even 5 days prior to the starting of the break in the lower and middle troposphere. The maximum easterly anomalies in the lower and the middle troposphere move northwards upto 20° N. The composite latitudinal time section of OLR anomaly show a large area of negative OLR anomaly extending from 20°S to 10°N. The area is defined as the Southern. Hemispheric Convective Zone ( SHCZ). The negative OLR anomaly (10 Wm-2 is noticed around 5° S to 0° N. It increases to 20 Wm-2 on the second day of the break on the same latitudinal belt. The daily OLR anomaly pattern shows that the area of the negative OLR anomaly around the equatorial region increases with the approach of a break epoch. The forecasting aspects of the commencement / cessation of the break have been also discussed.

Traveling 10-day Waves at Mid-latitudes in the Troposphere and Lower Stratosphere Revealed by Radiosonde Observations and MERRA-2 Data in 2020

Although the characteristics of the traveling 10-day waves (10DWs) above the middle stratosphere have been well explored, little research has been performed on the counterpart in the troposphere and lower stratosphere (TLS). In the present study, we use radiosonde observations and MERRA-2 data in 2020 to characterize traveling 10DWs in mid-latitudes in the TLS. Single-site observations in both hemispheres show that strong 10DW activities are always accompanied by strong eastward jets (10-13 km). MERRA-2 data indicates that in the troposphere the eastward-propagating modes with larger wavenumbers, i.e., E3, E4, E5 and E6 are dominant. While in the lower stratosphere the eastward- and westward-propagating modes with small zonal wavenumbers e.g., 1 and 2, are dominant. Further research on E3, E4, E5 and E6 modes in the troposphere of both hemispheres shows that all the wave activities are positively correlated to the background zonal wind. The refractive index squared reveal that a strong eastward jet is suitable for these four modes to propagate. However, just above the jet, the eastward wind decreases with altitude, and a thick evanescence region emerges above 15 km. E3, E4, E5 and E6 10DWs cannot propagate upward across the tropopause; as such this can explain why these four modes are weak or even indiscernible in the stratosphere and above. In the troposphere, E5 10DW at 32°S is the most dominant mode in 2020. A case study of the anomalously strong E5 10DW activity on May 12, 2020 indicates that the wave amplification resulted from the upward and equatorward transmission of wave energy flows. Moreover, the tropopause and equatorial region can prevent the propagations of wave energy flows of E5 10DW.

Bayesian method for estimating Weibull parameters for wind resource assessment in the Equatorial region: a comparison between two-parameter and three-parameter Weibull distributions

The two-parameter Weibull distribution has garnered much attention in the assessment of windenergy potential. The estimation of the shape and scale parameters of the distribution has broughtforth a successful tool for the wind energy industry. However, it may be inappropriate to use thetwo-parameter Weibull distribution to assess energy at every location, especially at sites wherelow wind speeds are frequent, such as the Equatorial region. In this work, a robust technique inwind resource assessment using a Bayesian approach for estimating Weibull parameters is firstproposed. Secondly, the wind resource assessment techniques using a two-parameter Weibulldistribution and a three-parameter Weibull distribution which is a generalized form of twoparameterWeibull distribution are compared. Simulation studies confirm that the Bayesianapproach seems a more robust technique for accurate estimation of Weibull parameters. Theresearch is conducted using data from seven sites in Equatorial region from 1o N of Equator to 19oSouth of Equator. Results reveal that a three-parameter Weibull distribution with non-zero shiftparameter is a better fit for wind data having a higher percentage of low wind speeds (0-1 m/s) andlow skewness. However, wind data with a smaller percentage of low wind speeds and highskewness showed better results with a two-parameter distribution that is a special case of threeparameterWeibull distribution with zero shift parameter. The results also demonstrate that theproposed Bayesian approach and application of a three-parameter Weibull distribution areextremely useful in accurate estimate of wind power and annual energy production.

Theoretical investigation of Fe–Rh binary nanoalloys: Chemical ordering and magnetic behavior

Gupta and Density Functional Theory (DFT) calculations were performed to investigate of structural and magnetic behaviors of 19 atom FenRh[Formula: see text] ([Formula: see text]–19) nanoalloys. A double icosahedron structure was considered for FenRh[Formula: see text] ([Formula: see text]–19) nanoalloys. Significantly, the effects of Fe atom addition on the chemical ordering, stability and total magnetic moments of the nanoalloys were investigated. Local optimization results at the Gupta level show that the Fe atoms are located in the center of the double icosahedron structure and finally in the equatorial region on the surface. The mixing energy analysis obtained that Fe[Formula: see text]Rh7 and Fe4Rh[Formula: see text] nanoalloys are the most stable compositions at Gupta and DFT levels, respectively. It was found that FenRh[Formula: see text] ([Formula: see text]–19) nanoalloys are energetically suitable for mixing at both Gupta and DFT levels. Also, the bond order parameter result is compatible with the mixing energy analysis result. The total magnetic moments of the FenRh[Formula: see text] ([Formula: see text]–19) nanoalloys increase with the addition of the Fe atom, which is a ferromagnetic metal.

Time and Altitude spread F echoes distribution over the Christmas Island VHF radar

The goal of this work is to study the time and altitude echoes characteristics under different solar and seasonality conditions using the VHF radar RTI images. The occurrence of equatorial spread F depends on the existence of conditions that can seed the Raileight-Taylor instability, and these conditions can change with solar flux, seasonality, longitude distributions, and day-to-day variability. So, the equatorial spread F is observed as its time and altitude occurrence. The VHF radar of Christmas Island (2.0° N, 157.4° W, 2.9° N dip latitude) has been operational in the equatorial region for some time now, allowing long-term observations. The occurrence of echoes during solar minimum conditions are observed all throughout the night since the post reversal westward electric field is weaker than the solar maximum and the possibilities for the vertical plasma drift to become positive are larger. On other hand, echoes during solar maximum will be controlled by dynamics near the time of the Pre-reversal Peak (PRE). Our results indicate peak time occurrence of echoes along this period shows a well-defined pattern, with echoes being distributed as closer to local sunset during solar maximum and around/closer midnight during solar minimum conditions, meanwhile, the peak altitude occurrence of echoes shows a slightly regular pattern with higher altitude occurrences during solar maxima and lower altitudes during solar minimum conditions.

Impact of Climate Change on Water Resources in Eastern Africa

Climate change is causing great impact on water resources in Eastern Africa, and there is need to establish and implement effective adaptation and mitigation measures. According to IPCC, less rainfall during the months that are already dry could increase drought as well as precipitation, and this has great impact on both permanent and seasonal water resources. Increased sea surface temperature as a result of climate change could lead to increased drought cases in Eastern African and entire equatorial region. Climate change will also result in annual flow reduction in various river resources available within the region such as the Nile River. IPCC predicts that rainfall will decrease in the already arid areas of the Horn of Africa and that drought and desertification will become more widespread, and as a result, there will be an increased scarcity of freshwater even as groundwater aquifers are being mined. Wetland areas are also being used to obtain water for humans and livestock and as additional cultivation and grazing land. This chapter reviews the climate change impacts on water resources within the Eastern Africa Region. The climate change impacts on different water resources such as Ewao Ngiro have been highlighted and projection of future climate change on water resources examined. Stream flow for Ewaso Ngiro was found to have a significant increasing trend in 2030s of RCP4.5 and non-significant decreasing trend in stream flow in 2060s for RCP4.5.

Statistical Study of Ionospheric Equivalent Slab Thickness at Guam Magnetic Equatorial Location

The ionospheric equivalent slab thickness (τ) is defined as the ratio of the total electron content (TEC) to the F2-layer peak electron density (NmF2), and it is a significant parameter representative of the ionosphere. In this paper, a comprehensive statistical analysis of the diurnal, seasonal, solar, and magnetic activity variations in the τ at Guam (144.86°E, 13.62°N, 5.54°N dip lat), which is located near the magnetic equator, is presented using the GPS-TEC and ionosonde NmF2 data during the years 2012–2017. It is found that, for geomagnetically quiet days, the τ reaches its maximum value in the noontime, and the peak value in winter and at the equinox are larger than that in summer. Moreover, there is a post-sunset peak observed in the winter and equinox, and the τ during the post-midnight period is smallest in equinox. The mainly diurnal and seasonal variation of τ can be explained within the framework of relative variation of TEC and NmF2 during different seasonal local time. The dependence of τ on the solar activity shows positive correlation during the daytime, and the opposite situation applies for the nighttime. Specifically, the disturbance index (DI), which can visually assess the relationship between instantaneous τ values and the median, is introduced in the paper to quantitatively describe the overall pattern of the geomagnetic storm effect on the τ variation. The results show that the geomagnetic storm seems to have positive effect on the τ during most of the storm-time period at Guam. An example, on the 1 June 2013, is also presented to analyze the physical mechanism. During the positive storms, the penetration electric field, along with storm time equator-ward neutral wind, tends to increase upward drift and uplift F region, causing the large increase in TEC, accompanied by a relatively small increase in NmF2. On the other hand, an enhanced equatorward wind tends to push more plasma, at low latitudes, into the topside ionosphere in the equatorial region, resulting in the TEC not undergoing severe depletion, as with NmF2, during the negative storms. The results would complement the analysis of τ behavior during quiet and disturbed conditions at equatorial latitudes in East Asia.

Bimodality in ensemble forecasts of 2 m temperature: identification

Bimodality and other types of non-Gaussianity arise in ensemble forecasts of the atmosphere as a result of nonlinear spread across ensemble members. In this paper, bimodality in 50-member ECMWF ENS-extended ensemble forecasts is identified and characterized. Forecasts of 2 m temperature are found to exhibit widespread bimodality well over a derived false-positive rate. In some regions bimodality occurs in excess of 30 % of forecasts, with the largest rates occurring during lead times of 2 to 3 weeks. Bimodality occurs more frequently in the winter hemisphere with indications of baroclinicity being a factor to its development. Additionally, bimodality is more common over the ocean, especially the polar oceans, which may indicate development caused by boundary conditions (such as sea ice). Near the equatorial region, bimodality remains common during either season and follows similar patterns to the Intertropical Convergence Zone (ITCZ), suggesting convection as a possible source for its development. Over some continental regions the modes of the forecasts are separated by up to 15 °C. The probability density for the modes can be up to 4 times greater than at the minimum between the modes, which lies near the ensemble mean. The widespread presence of such bimodality has potentially important implications for decision makers acting on these forecasts. Bimodality also has implications for assessing forecast skill and for statistical postprocessing: several commonly used skill-scoring methods and ensemble dressing methods are found to perform poorly in the presence of bimodality, suggesting the need for improvements in how non-Gaussian ensemble forecasts are evaluated.