Polarimetric Doppler Weather Radar Research Articles

Assessment of ISRO’s S-band polarimetric Doppler Weather Radar (DWR) at SHAR with IMD-DWR and GPM-Ku radar

ABSTRACT This paper describes the first assessment of ISRO’s indigenously developed S-band Polarimetric Doppler Weather Radar (DWR) at Sriharikota High Altitude Range (SHAR), Sriharikota (13.66°N, 80.23°E). The assessment is done during the passage of a tropical cyclone ‘Phethai’ and four different cases of Mesoscale convective systems. A comparison of reflectivity measured from SHAR-DWR with India Meteorological Department (IMD) DWR located at Chennai (13.07°N, 80.28°E) and Ku-band space-borne radar of the Global Precipitation Mission (GPM) is done using the common volume matching method. A good comparison is observed between SHAR-DWR with IMD-DWR and GPM-Ku radar in both space and height. The vertical structure of the cyclone is provided using Contour Frequency by Altitude Diagrams (CFAD) which show the vertical extent up to an altitude of 16 km with a reflectivity between 25 and 30 dBZ. Maximum occurrence of 30 dBZ occurs below 6 km. Bright band signatures show ~ 25 dBZ between 4 and 5 km depicting the stratiform precipitation of the cyclone. Further rain rate is estimated using both reflectivity and the polarimetric product which compared well with rain estimated from IMD-DWR and rainfall observed from rain gauges. Rain rate is observed from 5 to 35 mm hr−1. Hydrometer classification during the passage of tropical cyclone ‘Phethai’ shows the presence of rain below 4 km and graupels, ice crystals, and large droplets above.

Revealing the Precipitation Characteristics of Tropical Cyclone Ockhi from Polarimetric Doppler Weather Radar in Conjunction with Disdrometer Observations

Abstract This paper describes the rainfall and microphysical structure of precipitation associated with Tropical Cyclone Ockhi using polarimetric Doppler weather radar (PDWR) products. The study reports the statistical analysis of precipitation types of tropical cyclone cloud systems over the north Indian Ocean, by combining the observations of the PDWR and disdrometer for the first time. There are few studies that mention initial DWR observations of TC over this low-latitude region below 23.5°N. We tried to further carry out a statistical analysis of precipitating clouds in a cyclone from its depression stage to severe cyclonic stage. This study tries to classify and quantify the contribution of convective and stratiform rain to the total TC rainfall. Precipitating clouds have been classified into convective and stratiform based on reflectivity measurements. The vertical profiles (VPRs) of the radar reflectivity Z and the differential reflectivity ZDR obtained for the stratiform and the convective events are compared. A study of the VPR of the convective events reveals that the Z and ZDR parameters tend to increase as the raindrops descend toward the ground owing to enhanced collision–coalescence processes. The VPR of stratiform rain shows signatures of the bright band (BB). The drop size distribution (DSD) parameters and rainfall rate pertaining to the two different precipitation regimes are estimated from the radar data and have been compared. The Joss–Waldvogel Disdrometer measurements have been used to derive DSD parameters and polarimetric rain-rate relation.

Adopting a Neuro-Fuzzy Logic Method for Fall Armyworm Detection and Monitoring Using C-Band Polarimetric Doppler Weather Radar With Field Verification

Adopting a Neuro-Fuzzy Logic Method for Fall Armyworm Detection and Monitoring Using C-Band Polarimetric Doppler Weather Radar With Field Verification

Extreme precipitation over complex terrain using multiple remote sensing observation: A case study in the Great Bandung, Indonesia

Intense precipitation events are the main cause triggering hydrometeorological hazards over complex terrain. Two extreme precipitation (EP) events led to major flooding on 23–25 March 2021 and produced a rain-hail mixture (RHM) on 11 April 2021 in the Greater Bandung (GB) basin area, Indonesia. We investigated the spatial and vertical structure of precipitating cloud systems and the plausible mechanism triggering the two case studies with combined multiple remote sensing observations using an X-band polarimetric Doppler Weather Radar (Xpol) and X-band rain scanner radar (RSR) network, supported by rain gauges and satellite observation. The local processes controlling the intense rainfall events over the complex topography were quantified for the first time using an observational campaign in Indonesia. During the first EP event (23–25 March 2021), the modified satellite algorithm successively confirmed that the mesoscale convective system triggered the local anomalous circulation. The RSR network reveals that the EP in eastern GB contributed to the overflow of the Citarum River alongside the basin, coinciding with the eastward propagating convective system that produced oblate-shaped water droplets without hail. Nevertheless, during the second EP event on 11 April 2021, the strengthening of mountain-based convection played a main role in producing RHM, confirmed by a hail differential reflectivity larger than 12 dB and exhibited hail early stage over two height levels in different locations (981 m and 1033 m) in the GB. Our study also found Doppler vorticity-based and rain sizes combination indicators using RSR data networks in capturing such extreme weather events over complex topography with 35 min early times to support the early warning system of hydrometeorological disaster mitigation over GB, Indonesia.

Characterization of deep convective cells during the Indian summer monsoon using C-band polarimetric Doppler Weather Radar observations over Thumba (8.5o N, 77o E)

The vertical structure and dynamics of deep convective clouds plays an important role during the Indian summer monsoon period. The characteristics of deep convective cells (DCC) and their microphysics remain unclear, especially during the Indian summer monsoon (ISM). Further, the intensity of convection is an important element, which plays a key role in the progression of the monsoon. The present study focuses on characterizing DCC over a coastal location Thumba (8.50 N, 770 E) during the Indian summer monsoon periods of 2017, 2018 and 2019 using C-band polarimetric Doppler Weather Radar (DWR) measurements in terms of their intensity, vertical extent, top heights and their microphysical properties. A method is devised to identify the DCC from the DWR observed reflectivity cross-sections. The results showed that the occurrence of reflectivities in the range of 25–35 dBZ dominates below 6 km and the reflectivities in the range of 10–20 dBZ dominates above 6 km. The diurnal evolution of 40 dBZ depth radar echoes in DCC were analysed for June–September months, which showed peaks at preferential timings. The mean diurnal evolution of DCC also been investigated and it is found that these systems peak at three local time intervals viz., 00–05, 13–16 and 19–23 h during ISM period. Further, a separate analysis has been carried out for land and oceanic region for 40 dBZ depth radar echoes in DCC. The analysis show that the occurrence of 40 dBZ depth radar echoes peak at early-morning and late-night over the ocean and afternoon and late night over the land regions. The present results provide a quantitative assessment of DCC including their diurnal evolution during the Indian summer monsoon season over Thumba using DWR observations for the first time.

Structure and evolution of organized precipitation bands: C-band doppler weather radar observations over Thumba (8.5o N, 77o E)

In the present communication, C-band polarimetric Doppler Weather Radar (C-DWR) observations are used to investigate the structure and evolution of organized precipitation bands during the Indian summer monsoon (ISM) of 2017, 2018 and 2019 over Thumba (8.50 N, 770 E), a coastal location in south India. The C-DWR observations show organized high radar reflectivity structures of ∼50 dBZ that organized into narrow bands of ∼200 km (North-South) in length and 10–20 km (East-West) in width with vertical extent of ∼6–8 km. These narrow bands of precipitation structures are observed to be formed over the Arabian Sea and subsequently propagating towards the radar site. The observed differential radar reflectivity (Zdr) and the correlation co-efficient values indicate the horizontally oriented droplets and non-uniform hydrometeors. The potential formation mechanisms of the precipitation bands are investigated using reanalysis winds. The results show that blocking effect induced by the Western Ghats around the radar site play a key role in the formation of organized precipitation bands. It is noted that the location of the blocking effect induced convergence (conducive for the formation of precipitating clouds) with respect to the orography is proportional to the intensity of the low-level winds. The significance of the present study lies in understating the structure and evolution of organized precipitation bands and discussing their potential formation mechanisms during the ISM using C-DWR observations.

C-band polarimetric Doppler Weather Radar observations during an extreme precipitation event and associated dynamics over Peninsular India

C-band polarimetric Doppler Weather Radar observations during an extreme precipitation event and associated dynamics over Peninsular India

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.

C-band Doppler weather radar observations during the passage of tropical cyclone ‘Ockhi’

Recently, a C-band polarimetric Doppler weather radar (DWR) was installed and commissioned at Thumba (8.5° N, 77° E), a west coastal station in the southern peninsula of India known as ‘Gateway of Indian Summer Monsoon’, for monitoring severe weather events and tropical cyclones. The DWR operates in the frequency range of 5.6 to 5.65 GHz with a peak transmitting power of 250 kW and employs state-of-the-art technology for both transmitter and receiver subsystems. Apart from providing regular base products such as reflectivity (Zh), radial velocity (V) and spectral width (σ), the DWR being equipped with dual polarization capability provides additional products such as differential reflectivity (Zdr), differential phase shift (ϕdp) and correlation coefficient (ρhv), which are used to study the microphysical properties of rain bearing clouds. The ‘Ockhi’ cyclone was the most recent one from 29th November to 2nd December 2017, which caused large devastation in terms of both economic and human life in Kerala coastal places. The C-band polarimetric DWR provides an opportunity to investigate the spatial and vertical structure of ‘Ockhi’ cyclone over the south-west coast of Kerala. The cyclone ‘Ockhi’ developed near the west of Srilanka and later advanced and stretched out near south-east of Kanyakumari through the Arabian Sea and impacted the coastal places of Kerala on 1st December 2017. During its formative stage, the eyewall was not clearly visible. The cyclone eye was clearly seen at the well-developed stage of cyclone, when it was in the vicinity of DWR range. The overall spatial extent of cyclone is ~ 1000 km as seen in INSAT-3D images. The maximum surface wind speed was observed to be around 30 m/s near to the Kerala coast. The outer fringes of the cyclone were located above the Trivandrum and caused heavy rainfall on 30 November 2017 around 17 h. The C-band DWR has captured the various stages of cyclone ‘Ockhi’ and its primary bands. Observations of C-band polarimetric DWR indicates that the vertical cross section of reflectivity along the cyclone eye showed that the size of cyclone is around 20 km and the precipitating cloud top heights reaching as high as 10–12 km. The cyclone’s outer rainbands are slanted outward and were more intense than the inner rainbands. The area surrounding the cyclone eye is the eyewall, characterized by very strong wind and torrential rainfall. The large differential reflectivity values ranging from 2 to 3 dB are found in the eyewall and rainbands regions. The outer rainband is characterized by large Zdr values with high reflectivity above the melting layer. The different values of Zdr are observed in the eyewall and outer rainband regions, which suggest that different microphysical characteristics prevail. As time progress, the cyclone system gradually intensified and the eyewall became more intense compared to the outer ones. The present study utilizes the C-band polarimetric DWR observations to characterize the spatial and vertical structure of cyclone ‘Ockhi’ and provides the ample information on the polarimetric signatures of cyclone structure to improve the better understating on the microphysical characteristics of tropical cyclones.

Characteristics and Structure of the Cumulonimbus Cloud with Waterspout over the Gulf of Finland

The characteristics of the сumulonimbus cloud with waterspout that has passed over the Gulf of Finland are analyzed. The characteristics were obtained from polarimetric Doppler weather radar, radiometer, and lightning detector data. The waterspout was formed close to the cyclone center. The analysis of instability indices revealed high atmospheric instability. The sinking of the rotational motion in the cloud before the waterspout generation is shown. The radar characteristics of the cloud at the moment of waterspout observation are considered in detail. It is concluded that good identifiers for the waterspout detection are the “Zdr column” and the zone in the lower part of the cloud with differently directed values of Doppler velocity and with the high values of velocity spectrum width.

Validation of a Multilag Estimator on NJU-CPOL and a Hybrid Approach for Improving Polarimetric Radar Data Quality

For the estimation of weak echo with low signal-to-noise ratio (SNR), a multilag estimator is developed, which has better performance than the conventional method. The performance of the multilag estimator is examined by theoretical analysis, simulated radar data and some specific observed data collected by a C-band polarimetric radar in previous research. In this paper, the multilag estimator is implemented and verified for Nanjing University C-band polarimetric Doppler weather radar (NJU-CPOL) during the Observation, Prediction and Analysis of Severe Convection of China (OPACC) field campaign in 2014. The implementation results are also compared with theoretical analysis, including the estimation of signal power, spectrum width, differential reflectivity, and copolar correlation coefficient. The results show that the improvement of the multilag estimator is little for signal power and differential reflectivity, but significant for spectrum width and copolar correlation coefficient when spectrum width is less than 2 ms−1, which implies a large correlation time scale. However, there are obvious biases from the multilag estimator in the regions with large spectrum width. Based on the performance analysis, a hybrid method is thus introduced and examined through NJU-CPOL observations. All lags including lag 0 of autocorrelation function (ACF) are used for moment estimation in this algorithm according to the maximum usable lag number. A case study shows that this hybrid method can improve moment estimation compared to both conventional estimator and multilag estimator, especially for weak weather echoes. The improvement will be significant if SNR decreases or the biases of noise power in the conventional estimator increase. In addition, this hybrid method is easy to implement on both operational and non-operational radars. It is also expected that the proposed hybrid method will have a better performance if applied to S-band polarimetric radars which have twice the maximum useable lags in the same conditions with C-band radars.

Design of a Variable Depth Axially Corrugated Horn Antenna at X-Band for Low Cross-Polarization Applications

In this paper, the design of an axially corrugated conical horn antenna is presented for the application in a transportable polarimetric Doppler Weather Radar (DWR) at X-Band. Such types of applications require very low cross-polarization and the same is achieved for the current feed horn. Additionally, since it is to be used for transportable weather radar and the actual operating frequency depends at the corresponding site condition, the horn has been designed to operate the commonly used weather radar band of 9.3 GHz to 9.5 GHz. The proposed feed horn has five corrugations with variable depth and linear profile for the ease of fabrication. The horn was fabricated using aluminium material and measurements were carried out in Compact Antenna Test Facility (CATF). Measurement result confirms −18 dB of edge taper as requirement with a cross polarization of better −30 dB which are in good agreement with the simulated one. Measured data of the feed pattern is used to simulate in GRASP9 software package and the overall antenna performance ensures the fulfilment of required specifications for the polarimetric Doppler weather radar system.

Storm characteristics and precipitation estimates of monsoonal clouds using C-band polarimetric radar over Northwest India

Storm is a convective cell much smaller than a mesoscale convective system (MCS) but typically larger than a cumulonimbus cloud and heavy precipitation and lightning are often associated with it. Storms contribute major fraction of the convective precipitation in MCSs. Storm characteristics and precipitation estimates around New Delhi (28.6°N, 77.2°E; an Indian land location) during June–September period of the year 2013 are reported here using data of C-band polarimetric Doppler weather radar. Storms, defined based on radar reflectivity thresholds (30 dBZ for simple storms and 40 dBZ for intense storms), are tracked and their properties are extracted. Our results show that about 80% of storms exist for 1 h or less. The areas of 90% of simple storms are less than 100 km2 and the largest area averaged over storm lifespan does not exceed 400 km2. The majority of storms (> 80%) move with speeds less than 30 km h−1. About 60–65% of simple/intense storms have echo top heights between 6 and 10 km, while only few of them exceed 17 km. The values of average thickness of simple and intense storms lie between ~ 2–10 and ~ 1–7 km, respectively. It is not the vertical extent of a storm but its area-time integral that correlates better with the total precipitation amount. Around the New Delhi area, daily accumulated precipitation derived from relations incorporating polarimetric variables is in good agreement with the rain gauge measurements while that obtained from relations based on radar reflectivity factor (Zh) alone highly underestimates precipitation. This suggests that polarimetric capability is needed in Doppler weather radars to get the realistic precipitation estimates. The mean precipitation water content derived from Zh (~ 0.96 g m−3) is about 30–40% less compared to that derived from polarimetric relations. Our findings on storm properties have implications for cloud parameterizations and in short-term weather forecasting.

A new ash concentration estimation method using polarimetric data: The RMA observation of the 2015 Calbuco eruption

The Chilean volcano Calbuco erupted twice in 2015. The first eruption occurred at 21:04 UTC April 22nd, and the second at 04:00 UTC April 23rd. The ash cloud elevated to stratospheric levels, and extended hundreds of kilometers to the North East reaching Argentina. The RMA0, a polarimetric Doppler weather radar (located at San Carlos de Bariloche airport in Argentina, 124 km to the East) detected both clouds. The movement of the ash cloud could be followed in detail, and the height is reached, about 25 km, allowed an estimation of the total mass ejected: (4.4±0.7)×1011 kg for the first eruption and (1.9±0.3)×1012kg for the second. These estimates suggest this eruption should be classified by a VEI 4 or 5. A new formulation was developed to allow the use of Kdp and Zdr polarimetric radar variables to quantify the concentration of volcanic ash. Also ρhv is used to infer the change of behavior between early and later stages of the eruption.

Airborne polarimetric Doppler weather radar: trade-offs between various engineering specifications

Abstract. NCAR EOL is investigating potential configurations for the next-generation airborne phased array radar (APAR) that is capable of retrieving dynamic and microphysical characteristics of clouds and precipitation. The APAR will operate at C band. The APAR will use the electronic scanning (e-scan) feature to acquire the optimal number of independent samples for recording research-quality measurements. Since the airborne radar has only a limited time for collecting measurements over a specified region (moving aircraft platform ∼ 100 m s−1), beam multiplexing will significantly enhance its ability to collect high-resolution, research-quality measurements. Beam multiplexing reduces errors in radar measurements while providing rapid updates of scan volumes. Beamwidth depends on the size of the antenna aperture. Beamwidth and directivity of elliptical, circular, and rectangular antenna apertures are compared and radar sensitivity is evaluated for various polarimetric configurations and transmit–receive (T/R) elements. In the case of polarimetric measurements, alternate transmit with alternate receive (single-channel receiver) and simultaneous reception (dual-channel receiver) is compared. From an overall architecture perspective, element-level digitization of T/R module versus digital sub-array is considered with regard to flexibility in adaptive beamforming, polarimetric performance, calibration, and data quality. Methodologies for calibration of the radar and removing bias in polarimetric measurements are outlined. The above-mentioned engineering options are evaluated for realizing an optimal APAR system suitable for measuring the high temporal and spatial resolutions of Doppler and polarimetric measurements of precipitation and clouds.

Quality Analysis of Differential Phase Data for C-Band Dual- Polarimetric Doppler Weather Radar

Quality Analysis of Differential Phase Data for C-Band Dual- Polarimetric Doppler Weather Radar

Quantitative Differences between Lightning and Nonlightning Convective Rainfall Events as Observed with Polarimetric Radar and MSG Satellite Data

Abstract To increase understanding of the relationships between lightning and nonlightning convective storms, lightning observations from the National Aeronautics and Space Administration (NASA) African Monsoon Multidisciplinary Analyses (NAMMA) campaign were analyzed with Meteosat Second Generation (MSG) geostationary satellite and S-band NASA Polarimetric Doppler Weather Radar (NPOL) data. The study’s goal was to analyze the time evolution of infrared satellite fields and ground-based polarimetric radar during NAMMA to quantify relationships between satellite and radar observations for lightning and nonlightning convective clouds over equatorial Africa. Using NPOL data, very low-frequency arrival time difference lightning data, and MSG Spinning Enhanced Visible and Infrared Imager observations, the physical attributes of growing cumulus clouds, including ice mass production, updraft strength, cloud depth, and cloud-top glaciation were examined. It was found that, on average, the lightning storms had stronger updrafts (seen in the satellite and radar fields), which lead to the formation of deeper clouds (seen in the satellite and radar fields) and subsequently much more ice in the mixed-phase region (as confirmed in radar observations), as well as much more nonprecipitating ice in the top 1 km of the cloud (as quantified in both satellite and radar fields) than the nonlightning storms. Computed radar-derived ice masses in cumulus clouds verifies the traditional MSG indicators of cloud-top glaciation, while NPOL verifies internal structures (i.e., large amounts of graupel) where satellite and radar show strong updrafts.

Optimization of radome wall and joint for X-band reflector antenna using Floquet modal analysis

The performance of high frequency weather radars becomes questionable when the antenna system is enclosed by a radome because losses are more at higher frequency. To achieve high performance and accuracy, the radome wall and joints should be designed and optimized properly. Current manuscript presents the detailed study of A-sandwich radome wall and joint characteristics derived for polarimetric Doppler Weather Radar reflector antenna at X-band frequency. The diameter of the reflector antenna is 2.4 m which will be protected by a spherical A-sandwich radome of diameter 4.2 m. Radome wall is optimized by parametric variation of skin and core thickness using Floquet’s modal analysis in Ansoft HFSS Software package. Performances of radome panel with three different joint cross-sections have been compared in terms of insertion loss and phase variation and the best one is proposed for X-band antenna radome. Measurement was carried out at Compact Antenna Test Facility where the joint of two flat rectangular radome panels was hanged vertically in front of reflector antenna. Simulated results are compared with measured results to validate the proposed design.

Observations of Coastally Transitioning West African Mesoscale Convective Systems during NAMMA

Observations from the NASA 10 cm polarimetric Doppler weather radar (NPOL) were used to examine structure, development, and oceanic transition of West African Mesoscale Convective Systems (MCSs) during the NASA African Monsoon Multidisciplinary Analysis (NAMMA) to determine possible indicators leading to downstream tropical cyclogenesis. Characteristics examined from the NPOL data include echo-top heights, maximum radar reflectivity, height of maximum radar reflectivity, and convective and stratiform coverage areas. Atmospheric radiosondes launched during NAMMA were used to investigate environmental stability characteristics that the MCSs encountered while over land and ocean, respectively. Strengths of African Easterly Waves (AEWs) were examined along with the MCSs in order to improve the analysis of MCS characteristics. Mean structural and environmental characteristics were calculated for systems that produced TCs and for those that did not in order to determine differences between the two types. Echo-top heights were similar between the two types, but maximum reflectivity and height and coverage of intense convection (>50 dBZ) are all larger than for the TC producing cases. Striking differences in environmental conditions related to future TC formation include stronger African Easterly Jet, increased moisture especially at middle and upper levels, and increased stability as the MCSs coastally transition.