Structure of the Kakinada cyclone of 6 November 1996

Radar is a very powerful tool in determining the position, speed and direction of movement, horizontal and vertical extent of the cyclone. Besides, the radar observations can also be expected to provide more vital information on the shape, size and behaviour of the eye of a cyclone. These features are very important input information for cyclone forecasting, especially in assessing the intensity of the cyclone. An effort has been made here to document the above features of a cyclone that struck the east Godavari coast in November 1996. The cyclone formed over central Bay of Bengal in the afternoon of 5 November 1996 and intensified into a severe cyclonic storm with a core of hurricane winds next day. The cyclone was tracked by Cyclone Detection Radar (CDR) Visakhapatnam from the initial stage of its formation till it crossed the coast near Kakinada. In this paper, the radar track of the cyclone over sea, along with the size. shape and behaviour of the eye as observed on radar have been discussed. The variation of other parameters like eyewall width, radius of maximum reflectivity and wall cloud height and relationship between eyewall width and eye diameter have also been discussed.

Characteristic features of Orissa super cyclone of 29th October, 1999 as observed through CDR Paradip

lkj & bl 'kks/k&Ik= esa 29 vDrwcj] 1999 esa mM+hlk ds rV ij vk, egkpØokr ds Øfed fodkl ds jsMkj ls izkIr gq, vfHky{k.kksa dks izysf[kr djus dk iz;kl fd;k x;k gSA 280800 ;w- Vh- lh- vkSj 290200 ;w- Vh- lh- ds e/; fy, x, 18 ?kaVs dh vof/k ds ih- ih- vkbZ- fp=ksa ls rS;kj fd, x, /kzqoh; vkjs[kksa ds fo’ys"k.k ls bl egkpØokr ds Øfed fodkl ds jkspd igyqvksa dk irk pyk gSA bl fo’ys"k.k ls izkIr gq, izcyhdj.k ds ladsr izs{k.k dh vU; iz.kkfy;ksa ds mi;ksx ls izkIr gq, fo’ys"k.kksa ds vuq:Ik ik, x, gSaA An attempt is made to document the radar observed features of evolution of super cyclone that hit Orissa on 29 October, 1999. Analysis of polar diagrams comprising of hourly PPI images taken between 280800 UTC and 290200 UTC reveals interesting aspects of development of this Super Cyclone in terms of waxing and waning of eye size in relation to intensification process. The smallest radius of maximum reflectivity is in conformity with the colossal death toll observed close to the track of the super cyclone. Structural changes observed through radar images are in conformity with intensify changes as seen through other observing systems.

Highly reflective and conductive AlInN/GaN distributed Bragg reflectors realized by Ge-doping

We report on the realization of highly conductive and highly reflective n-type AlInN/GaN distributed Bragg reflectors (DBR) for use in vertical cavity surface emitters in a metalorganic vapor phase epitaxy process. While Ge-doping enables low-resistive n-type GaN/AlInN/GaN heterostructures, very high Ge doping levels compromise maximum optical reflectivities of DBRs. Simulations of the Bragg mirror's reflectivities together with structural analysis by X-ray diffraction reveal an increased absorption within the doped AlInN layers and interface roughening as major causes for the observed reduction of the optical reflectivity. By adjusting the Ge doping level in the AlInN layers, this structural degradation was minimized and highly conductive, 45-fold AlInN/GaN DBR structures with a maximum reflectivity of 99 % and vertical specific resistance of 5x10-4 Ωcm2 were realized.

Analysis of three unusual severe weather events over Delhi during May-June, 2018 using Dual-Pol Doppler Weather Radar and GNSS data

High-impact weather events, such as thunderstorms and dust storms, are aspects of a changing climate that are likely to have an adverse effect on society. A number of such severe weather events struck Delhi and adjoining areas during the months of April, May and June of the year 2018. Three events observed during May-June have been analyzed using observations from C-Band Polarimetric Doppler Weather Radar (DWR) and ground based Global Navigational Satellite (GNSS) receiving system installed at Mausam Bhawan, New Delhi. Here, an attempt has been made to study the data regarding these unusual events from DWR observations especially of polarimetric nature and cross verify it with the data obtained from GNSS receiving system. Reflectivity of more than 60 dbZ was observed in all the events by the DWR system except on 9 June when a squall line formed with maximum reflectivity around 54 dBZ and the wind velocity increased upto 120 knots on the same date on few occasions and generally varied between 45-60 knots during the period of the storms. The height of these storms varied between 12 kms and 13.6 kms except on 9 June when the storm height was observed to be more than 15 kms by the DWR. Though the maximum reflectivity was a bit less on 9th June but the vertical extent of the clouds was greater and therefore the estimated value of IPWV from GNSS had a maximum of 67 mm as compared to the values in the range of 40 to 45 mm for other storm events. Apart from the single-pol DWR observations, the dual-pol products presented a more comprehensive ingredients of the storms in respect of the size, shape and variety of the hydrometeors and also their non-meteorological nature. The information regarding the concentration of hydrometeors has also been a positive point while analyzing through the eyes of a dual-pol radar. These multiple thunderstorms have been discussed to bring out some of their important features and a good amount of agreement has been observed between the data obtained from dual-pol DWR system and GNSS.

Optimal parameters for fiber Bragg gratings for sensing applications: a spectral study

The spectral characteristics viz. reflectivity, bandwidth, and sidelobes’ intensity for uniform and apodized (Gaussian, hyperbolic tangent, apod1, sine, and raised sine) fiber Bragg gratings (FBGs) were studied as a function of grating length and index modulation. The optimal grating length and index modulation to obtain maximum reflectivity and minimum sidelobes were determined, as needed for sensing applications. The impact of various apodization profiles on the spectral response has also been assessed. The results indicate that out of the apodization profiles considered for the study, sine, Gaussian, and raised sine profiles offer the desired output. Article highlights The reflectivity (of main peak) and sidelobes’ intensity increase with grating length and index modulation. The bandwidth decreases with grating length and increases with index modulation. The ideal grating length and index modulation were found to be 5 mm and 0.0008 respectively to obtain maximum reflectivity and minimum intensity for sidelobes. Sine, Gaussian, and raised sine profiles are the best suitable apodization profiles among those considered.

Thumb Rule for Nowcast of Dust Storm and Strong Squally Winds over Delhi NCR using DWR Data

ABSTRACTSqually winds are the natural hazards and are often associated with the severe thunderstorms (TS), which mostly affects plains of North West India during pre monsoon season (March to May). Squally winds of the order more than 60 kmph are very devastating. Under influence of these strong squally winds trees, electricity poles, advertisement sign boards fall, sometimes human life is also lost. The main objective of this study is to find out the thumb rule based on Doppler Weather Radar (DWR) Data to Nowcast the squally winds over a region. To detect thumb rule, five cases of thunder storm accompanied with squally winds ranging from (55 kmph to 110 kmph) are taken in to consideration. These TS’s occurred over Delhi NCR (National Capital Region) during May – June 2018. Maximum reflectivity (Max Z) data of Delhi DWR, Cloud Top Temperature (CTT) data from INSAT and squally winds along with other weather parameters observed at Safdarjung and Palam observatories are utilized to find out the Thumb Rule.Based on the analysis, it is concluded that presence of a western disturbance (WD), presence of East-West trough from North-west Rajasthan upto East UP through south Haryana and very high temperature of the order of 40 degree Celsius over the nearby area are very conducive for occurrence of squally winds accompanied with thunderstorms. Thumb rule find out in this study is that, squally winds of the order of 55 kmph or more will effect a station if a thunderstorm (having Max Z echo with vertical extension of cell >7 km, reflectivity >45 dBz and at a distance of more than 100 km from the station) moving towards station is present in one to two hour before images of Doppler Weather Radar.

Fireworks on Weather Radar and Camera

High-sensitivity weather radars easily detect nonmeteorological phenomena characterized by weak radar returns. Fireworks are the example presented here. To understand radar observations, an experiment was conducted in which the National Severe Storms Laboratory (NSSL)’s research (3-cm wavelength) dual-polarization radar and a video camera were located at 1 km from fireworks in Norman, Oklahoma. The fireworks from the 4 July 2017 celebration were recorded by both instruments. The experiment is described. Few bursts recorded by the camera are analyzed to obtain the height of the explosion, its maximum diameter, number of stars, and the duration of the visible image. Radar volume scans are examined to characterize the height of the observation, the maximum reflectivity, and its distribution with height. The fireworks location is close to the Terminal Doppler Weather Radar (TDWR) that operates in single polarization at a 5-cm wavelength and monitors hazardous weather over the Oklahoma City airport. A third radar with data from the event is the Weather Surveillance Radar-1988 Doppler (WSR-88D) located in Norman. It has a wavelength of 10 cm and supports technical developments at the Radar Operation Center. Reflectivity factors measured by the three radars are compared to infer the size of dominant scatterers. The polarimetric characteristics of fireworks returns are analyzed. Although these differ from those of precipitation, they are indistinguishable from insect returns. Radar observation of larger fireworks in Fort Worth, Texas, with a WSR-88D is included and compared with the observations of the smaller fireworks in Norman. We expect the detectability of explosions would be similar as of fireworks. Pinpointing locations would be useful to first responders, or air quality forecasters. A benefit of fireworks recognition in weather radar data is that it can prevent contamination of precipitation accumulations.

Kajian Quasi Linear Convective System Di Bengkulu Pada Tanggal 10 November 2017 Menggunakan Wrf-Arw

<p class="AbstractEnglish"><strong>Abstract: </strong>The Quasi Linear Convective System (QLCS) is a meso-scale convective weather system that has the potential to bring heavy rains and destructive strong winds. One of the Quasi Linear Convective Systems (QLCS) that have occurred in Indonesia is the QLCS that was formed in Bengkulu on November 10, 2017. QLCS can be identified using weather radar observations through maximum reflectivity imagery that forms long lines. WRF-ARW (Weather Research and Forecasting - Advanced Research) weather modeling is able to simulate meso-scale atmospheric conditions. This study aims to examine the phenomenon of QLCS using identification of weather radar observations and the results of WRF-ARW modeling. The results showed a QLCS with a length of 82 km, began to form at 09:30 UTC and reached its peak at 10.50 UTC with a maximum reflectivity of 63 dBz. Atmospheric dynamics conditions in the form of wind / streamline patterns, vertical velocity, relative humidity, Convective Available Potential Energy (CAPE) and cloud fraction from WRF-ARW model outputs show a suitable pattern and support the occurrence of convective systems around the scene. Wind patterns at the time of the event indicate a convergence region. Meanwhile the vertical velocity value reaches a peak of 0.8 Pa / s before QLCS starts entering the mature phase. The relative humidity is 95% - 100% and the CAPE value reaches 1000 J / Kg to 1500 J / Kg. Cloud fraction in the layer near the surface reaches 1%. Verification results with observational data show that rainfall parameters produce smaller errors compared to the results of verification reflectivity values. This shows that the WRF-ARW model is still inaccurate in modeling reflectivity data.</p><p class="AbstrakIndonesia"><strong>Abstrak: </strong><em>Quasi Linear Convective System</em> (QLCS) merupakan sistem cuaca konvektif skala meso yang berpotensi membawa hujan lebat dan angin kencang yang sifatnya merusak. Salah satu <em>Quasi Linear Convective System</em> (QLCS) yang pernah terjadi di Indonesia adalah QLCS yang terbentuk di Bengkulu pada tanggal 10 November 2017. QLCS dapat diidentifikasi menggunakan pengamatan radar cuaca melalui citra <em>reflectivity</em> maksimum yang membentuk garis memanjang. Pemodelan cuaca WRF-ARW (<em>Weather Research and Forecasting </em><em>–</em><em> Advanced Research</em>) mampu mensimulasikan kondisi atmosfer skala meso. Penelitian ini bertujuan untuk mengkaji fenomena QLCS dengan menggunakan identifikasi pengamatan radar cuaca dan hasil permodelan WRF-ARW. Hasil penelitian menunjukkan QLCS dengan panjang 82 km, mulai terbentuk pada pukul 09.30 UTC dan mencapai puncaknya pada pukul 10.50 UTC dengan <em>reflectivity</em> maksimum 63 dBz. Kondisi dinamika atmosfer yang berupa pola angin/<em>streamline</em>, <em>vertical velocity</em>, kelembapan relatif,<em> Convective Available Potential Energy</em> (CAPE) dan <em>cloud fraction</em> hasil keluaran model WRF-ARW menunjukan pola yang sesuai dan mendukung terjadinya sistem konvektif di sekitar lokasi kejadian. Pola angin pada waktu kejadian menunjukan adanya daerah konvergensi. Sementara itu nilai <em>verti</em><em>c</em><em>al</em> <em>velocity</em> mencapai puncaknya 0.8 Pa/s pada saat sebelum QLCS mulai memasuki fase matang. Kelembaban relatif sebesar 95% - 100% dan nilai CAPE mencapai 1000 J/Kg hingga 1500 J/Kg. <em>Cloud fraction</em> di lapisan dekat permukaan mencapai 1 %. Hasil verifikasi dengan data observasi menunjukan parameter curah hujan menghasilkan <em>error </em>yang lebih kecil dibandingkan dengan <em>error</em> hasil verifikasi nilai <em>reflectivity</em>. Hal tersebut menunjukan bahwa model WRF-ARW masih kurang akurat dalam memodelkan data <em>reflectivity</em><em>.</em></p>

Characteristics of the Supercell Cb Thunderstorm and Electrical Discharges on 19 August 2015, North Caucasus: A Case Study

The development of extremely powerful thunderstorm which took place on August 19, 2015 is discussed in this paper. High depth hail cloud originated on the Black Sea Coast and classified as a supercell as well as several weaker hailstorms passed more than 1000 km over Northern Caucasus of Russia, the Caspian Sea, and then invaded the territory of Kazakhstan. During more than 20 hours of existence this supercell produced heavy hail, rain, intense lightning discharges, gust and tornado which rarely occurs in the region. The study of the structure and characteristics of the thunderstorm during the formation of electrical discharges and their frequency were of particular interest. According to the forecast, development of convective clouds and separate thunderstorms were expected, though the powerful hail process was not expected due to small vertical temperature gradients and the absence of cold fronts. Supercell was tracked by 5 radars located in this area, which showed its right-hand development with clock-wise deviation from the leading stream on 40-50 degrees to the right and the resulting speed of propagation was about 60-85km/h. The maximum reflectivity factor exceeded value 75dBZ, top of the clouds reached 15-16km and the height of the hail core raised on 11.2km. The size of hailstones size on most of the hail path was 2&ndash;3cm, and at the peak of cloud development - 4&ndash;5cm. Maximum frequencies of cloud-to-ground flashes of negative and positive polarities reached 30-35min-1 and 60-70min-1 correspondingly, while frequency of cloud-to-cloud flashes was significantly higher and amounted up to 300-500min-1 at the peak of the supercell development. An important fact is that the maximum frequency of flashes of different types coincided in time, showing that the reason of all discharges is similar. Total current of the cloud-to-ground flashes of positive and negative polarities was almost identical in magnitude and differed by sign. It was 200-300 kiloampere at the peak of thunderstorm development. The minimum value of radiation temperature, measured by SEVIRI radiometer installed onboard of Meteosat-10 satellite in 10.8 &mu;m channel, was near to -60&ordm;C. The minimum temperature value on the top of the supercell was comparable to coupled radar and sounding data. The most intensive precipitation flux derived from radiometric measurements was about 22000m3/sec; at the same period radars assessments showed precipitation up to 550mm/h (mixed phase precipitation) and size of hail 4.5cm. The combined satellite-radar-lightning data analysis showed that radar derived characteristics of the supercell reached their maximums earlier than maximum in lightning activity. The highest correlation coefficient between radar and lightning characteristics of the supercell storm was found for pair maximum reflectivity and intensity of LF (0.55) and VHF (0.66) discharges. Estimations of relationship between hail size and lightning activity showed that with increasing hail size, thunderstorm activity increases for both cloud-to-ground and intracloud flashes (on the level 0.46 - 0.59). Analysis of doppler-polarimetric data showed strong inflow zone associated with tornado. Tornadic debris signature was manifested by radar reflectivity factor ZH &gt; 60 dBZ, differential reflectivity ZDR &gt; -1 dB, copolar cross-correlation coefficient &rho;HV &lt; 0.6, and it was collocated with the tornado vortex signature. Doppler velocities in mesocyclone zone reached values -43 and +63 m/s. Prominent radar echo hook was identified in 1.5 km layer above the ground, while ZDR columns was relatively narrow (4&ndash;8 km wide) and not very deep (4.5 km).

The Impact of Microphysics Parameterization in the Simulation of Two Convective Rainfall Events over the Central Andes of Peru Using WRF-ARW

The present study explores the cloud microphysics (MPs) impact on the simulation of two convective rainfall events (CREs) over the complex topography of Andes mountains, using the Weather Research and Forecasting- Advanced Research (WRF-ARW) model. The events occurred on December 29 2015 (CRE1) and January 7 2016 (CRE2). Six microphysical parameterizations (MPPs) (Thompson, WSM6, Morrison, Goddard, Milbrandt and Lin) were tested, which had been previously applied in complex orography areas. The one-way nesting technique was applied to four domains, with horizontal resolutions of 18, 6, and 3 km for the outer ones, in which cumulus and MP parameterizations were applied, while for the innermost domain, with a resolution of 0.75 km, only MP parameterization was used. It was integrated for 36 h with National Centers for Environmental Prediction (NCEP Final Operational Global Analysis (NFL) initial conditions at 00:00 UTC (Coordinated Universal Time). The simulations were verified using Geostationary Operational Environmental Satellites (GOES) brightness temperature, Ka band cloud radar, and surface meteorology variables observed at the Huancayo Observatory. All the MPPs detected the surface temperature signature of the CREs, but for CRE2, it was underestimated during its lifetime in its vicinity, matching well after the simulated event. For CRE1, all the schemes gave good estimations of 24 h precipitation, but for CRE2, Goddard and Milbrandt underestimated the 24 h precipitation in the inner domain. The Morrison and Lin configurations reproduced the general dynamics of the development of cloud systems for the two case studies. The vertical profiles of the hydrometeors simulated by different schemes showed significant differences. The best performance of the Morrison scheme for both case studies may be related to its ability to simulate the role of graupel in precipitation formation. The analysis of the maximum reflectivity field, cloud top distribution, and vertical structure of the simulated cloud field also shows that the Morrison parameterization reproduced the convective systems consistently with observations.