Lower Atmospheric Wind Profiler Research Articles

Wind Profiler for Understanding of Meiyu at Dongshan

Abstract: To understand the Meiyu Boundary layer evolutionand vertical structure of precipitating cloud systems over Dongshan, special observational campaigns have been conducted downstream of the Yangtze River during June and July in the years 2001 and 2002. We deployed a Lower Atmospheric Wind Profiler (LAWP) with Radio Acoustic Sounding System (RASS) at the Meteorological Observatory, Dongshan within a mesoscale network that consists of three X-band Doppler radars, three AWS, and Micro rain radar to observe the inner structure of precipitating cloud systems seen frequently in the observational area. The LAWP provides vertical profiles of three-dimensional wind, vertical structure of the precipitating cloud system, convective boundary layer (CBL), and temperature from the (RASS) lower atmosphere with a height resolution of 60 m to 200 m and a time resolution of about 1 to 60 minutes. LAWP had been operated in two modes: low mode and high mode up to 4 km and 11 km height during non-rainy and rain conditions, respectively. A study was carried out during an intensive observational period (IOP-2001 and IOP-2002) to understand the pre-convective environments in the boundary layer during pre-Meiyu and Meiyu convective days to find out whether there is any precursor before the convection triggering. Further in Meiyu precipitating cloud systems, the reflectivity vertical structure can be used to identify the range of precipitation processes from the young, dynamically vigorous cells to the mature, bright band resolved stratiform rain.

Balloon-borne aerosol–cloud interaction studies (BACIS): field campaigns to understand and quantify aerosol effects on clouds

Abstract. A better understanding of aerosol–cloud interaction processes is important to quantify the role of clouds and aerosols on the climate system. There have been significant efforts to explain the ways aerosols modulate cloud properties. However, from the observational point of view, it is indeed challenging to observe and/or verify some of these processes because no single instrument or platform has been proven to be sufficient. Discrimination between aerosol and cloud is vital for the quantification of aerosol–cloud interaction. With this motivation, a set of observational field campaigns named balloon-borne aerosol–cloud interaction studies (BACIS) is proposed and conducted using balloon-borne in situ measurements in addition to the ground-based (lidar; mesosphere, stratosphere and troposphere (MST) radar; lower atmospheric wind profiler; microwave radiometer; ceilometer) and space-borne (CALIPSO) remote sensing instruments from Gadanki (13.45∘ N, 79.2∘ E), India. So far, 15 campaigns have been conducted as a part of BACIS campaigns from 2017 to 2020. This paper presents the concept of the observational approach, lists the major objectives of the campaigns, describes the instruments deployed, and discusses results from selected campaigns. Balloon-borne measurements of aerosol and cloud backscatter ratio and cloud particle count are qualitatively assessed using the range-corrected data from simultaneous observations of ground-based and space-borne lidars. Aerosol and cloud vertical profiles obtained in multi-instrumental observations are found to reasonably agree. Apart from this, balloon-borne profiling is found to provide information on clouds missed by ground-based and/or space-borne lidar. A combination of the Compact Optical Backscatter AerosoL Detector (COBALD) and Cloud Particle Sensor (CPS) sonde is employed for the first time in this study to discriminate cloud and aerosol in an in situ profile. A threshold value of the COBALD colour index (CI) for ice clouds is found to be between 18 and 20, and CI values for coarse-mode aerosol particles range between 11 and 15. Using the data from balloon measurements, the relationship between cloud and aerosol is quantified for the liquid clouds. A statistically significant slope (aerosol–cloud interaction index) of 0.77 found between aerosol backscatter and cloud particle count reveals the role of aerosol in the cloud activation process. In a nutshell, the results presented here demonstrate the observational approach to quantifying aerosol–cloud interactions.

Impact of land surface physics on the simulation of boundary layer characteristics at a tropical coastal station

Abstract In this study the influence of land surface physics on the simulation of Planetary Boundary Layer (PBL) characteristics in the Advanced Research Weather Research and Forecast (WRF-ARW) is examined at the tropical costal station Kalpakkam. High resolution simulations were conducted using WRF-ARW with two land surface models (LSM) (Noah and Noah MP) for winter (2–5 February 2011) and South West (SW) monsoon (15–18 September 2010). Data from a Lower Atmospheric Wind Profiler (LAWP), GPS-Sonde, meteorological towers and sonic anemometer were used to analyze the PBL properties. Significant variation in the surface and PBL properties were noticed in the simulations with the two LSMs and various features of the PBL were produced better by Noah MP than Noah. The Noah because of higher exchange coefficients simulated more warm and humid boundary layers compared to the Noah MP. In the study region higher (lower) sensible heat flux is simulated compared to the latent and soil heat fluxes during the dry winter (rainy SW monsoon). The variation in the surface energy partitioning resulted in a variation in the simulated PBL depth by the two LSMs. The PBL simulated by Noah MP was shallower than the Noah. During winter higher Bowen ratio associated with the Noah MP resulted in stronger entrainment of upper dry air which suppressed the vertical growth of the PBL. Whereas in SW monsoon, the convective and mechanical turbulence simulated by Noah MP was less than that of Noah, which has lead to a shallow PBL in Noah MP. Overall, the Noah MP simulated the thermodynamical structure, winds and vertical extent of the PBL better than Noah. The improvement in simulations with Noah MP are due to the explicit treatment of plant canopy, snow and ground surface, tiling scheme for vegetation and bare soil, and due to moderate exchange coefficients for soil heat and moisture.

IJARCCE - Computer and Communication Engineering

Lower Atmospheric Wind Profiler (LAWP) is used to provide continuous high resolution wind measurements in the lower atmosphere. Signal processing of this atmospheric radar is necessary to estimate the wind profiler moments and signal to noise ratio (SNR). The signals, which are processed in the present work has been obtained from the LAWP at National Atmospheric Research Laboratory (NARL), Gadanki, India. SNR computation is an important parameter in signal processing. This paper discusses improvement of SNR using wavelets for LAWP signals. In this paper wavelet denoising is used to improve SNR. Denoising is performed by selecting a DB10 wavelet. SNR for this data is computed for original signal and de-noised signal. Results show that there is 7dB improvement in SNR after denoising using DB10 wavelet for LAWP signals.

Statistical Characteristics of Multipeak Raindrop Size Distributions at the Surface and Aloft in Different Rain Regimes

Abstract Two years (∼672 h) of lower-atmospheric wind profiler (LAWP) and 4 yr (∼733 h) of Joss–Waldvogel disdrometer measurements are utilized to study the multipeak (MP) occurrence statistics at the surface and aloft. For the first time, an attempt has been made to address several key questions regarding MPs: their occurrence statistics and their dependency on height, season, and type of precipitation. MPs are not exceptional; rather, they are observed at all altitudes, albeit with different occurrence percentages. The occurrence of MPs seems to be height dependent, and this dependency varies with the type of rain system. The occurrence percentage of bimodal echo (two peaks) is high above (below) the melting level (ML) in convection (in other types of rain). The percentage occurrence of bimodal echo in warm rain is similar to that in cold rain, but only below the ML. The spectrum with more than two peaks appears to be predominantly in convection, particularly above 4 km. The MP statistics on the surface DSD derived from disdrometer data also support the profiler statistics qualitatively (occurrence is more likely in convection); however, the magnitudes of the percentage of occurrence are different at the surface and aloft. The peaks in the raindrop size distribution (DSD) spectra exist predominantly in drop diameter ranges of 0.45–0.65 and 0.9–1.3 mm in all types of rain, consistent with earlier numerical and observational studies. The MP occurrence does not have seasonal dependence aloft, but shows some variation at the surface with a larger percentage of the occurrences in the southwest monsoon. However, peaks in the surface DSD exist at same diameters in both monsoon seasons.

High resolution observations of turbulence in the troposphere and lower stratosphere over Gadanki

Abstract. High resolution (150 m) wind measurements from 13–17 July 2004 by Mesosphere-Stratosphere-Troposphere (MST) radar and 15–16 July 2004 by Lower Atmospheric Wind Profiler (LAWP) have been used to study the time variation of turbulence intensity. Layers of higher turbulence are observed in the lower stratosphere on 15–16 July which give rise to mixing in the region. Enhancement in short-period gravity wave activity and turbulent layers are observed after 22:00 LT which could be due to a dry convection event that occurred at that time. The breakdown of the convectively generated high frequency waves seems to have given rise to the turbulence layers. Wind shear is found to be high above the easterly jet, but very poor correlation is observed between square of wind shear and turbulence parameters in the region. The heights of the turbulent layers in the lower stratosphere do not correlate with levels of minimum Richardson number. A monochromatic inertia gravity wave could be identified during 13–17 July 2004. A non-linear interaction between the waves of different scales as proposed by Hines (1992) might also be responsible for the breakdown and generation of turbulence layers.

Multipeak Raindrop Size Distribution Observed by UHF/VHF Wind Profilers during the Passage of a Mesoscale Convective System

Abstract The Indian Mesosphere–Stratosphere–Troposphere radar (IMSTR), Lower Atmospheric Wind Profiler (LAWP), and Joss–Waldvogel (JW) disdrometer measurements during the passage of two distinctly different (in terms of total rain and rainfall rate) convective storms are utilized to understand the nature and origin of the multipeak raindrop size distribution (MRDSD). Important issues, such as the preferential stage and height at which bi- or multimodal rain distribution occurs in a mesoscale convective system (MCS) are addressed. For both of the storms, the MRDSD is observed during the transition period from convection to stratiform rain. The pattern and variation of the MRDSD during this period is strikingly similar in both of the storms. The MRDSD is first observed above the freezing level in the presence of heavy riming. The subsequent spectra have shown bimodal distribution below the freezing level, and the bimodality is attributed to the coexistence of ice and supercooled droplets. Interestingly, the bimodal distribution has not varied much with altitude when it is produced because of the coexistence of ice and supercooled droplets. The MRDSD is also observed at few range gates and for a short duration. Such a type of MRDSD is seen during the transition period between decaying and intensifying rain.

Classification of Tropical Precipitating Systems Using Wind Profiler Spectral Moments. Part I: Algorithm Description and Validation

Abstract The lower atmospheric wind profiler (LAWP) measurements made at Gadanki, India, have been used to develop an objective algorithm to classify the tropical precipitating systems. A detailed investigation on the existing classification scheme reveals major shortcomings in the scheme. In the present study, it is shown with examples that the Doppler velocity gradient (DVG) criterion is a necessary but certainly not a sufficient condition to identify the radar bright band. Such gradients in Doppler velocity can exist in other types of rain systems, for example, in convection, due to the modulation of Doppler velocity of hydrometeors by vertical air motion. The approach of the new classification scheme deviates considerably from that of existing algorithms. For instance, the new algorithm, in contrast to identifying the stratiform rain and assuming the remaining rain as convection, identifies first convection and later stratiform precipitation based on their specific characteristics. The other interesting feature in this algorithm is that it was built on the strengths of other potential classification schemes and theoretically accepted thresholds for classification of the precipitation. The performance of the new algorithm has been verified with the help of time–height maps of profiler moments and corresponding surface rainfall patterns.

Onset of Indian summer monsoon over Gadanki (13.5°N, 79.2°E): Study using lower atmospheric wind profiler

The onset of Indian summer monsoon (ISM) over Gadanki (13.5°N; 79.2°E) is identified using variations in signal‐to‐noise ratio (SNR), wind speed, wind direction and vertical velocity at 1.5 km (∼850 hPa) using lower atmospheric wind profiler (LAWP). Strengthening of the low level wind speed attaining 8 ms−1 with directional change from south‐easterlies to south‐westerlies defines the beginning of the monsoon. Enhancement in SNR few days before with noticeable magnitude of 5–10 dB at the time of onset combined with clear‐air vertical velocity reversal from downward to upward few days before onset and persisting during monsoon activity supplements the wind speed criteria in identifying onset. Hydrometeor velocity shows large downward values exceeding more than 1 ms−1 indicating occurrence of rainfall. It is proposed that UHF radar at a location can be used to identify the onset of ISM based on wind speed without considering rainfall separately.

Diurnal and seasonal variability of TKE dissipation rate in the ABL over a tropical station using UHF wind profiler

This paper presents the diurnal and seasonal variation of Turbulence Kinetic Energy (TKE) dissipation rate ( ε) in the Atmospheric Boundary-Layer (ABL) over a tropical station, Gadanki (13.5° N, 79.2° E) in India. Doppler spectral width measurements made by Lower Atmospheric Wind Profiler (LAWP) operating at 1357 MHz are utilized to estimate ε in the height region of 0.5–4.0 km on clear air days. Various non-turbulent spectral broadenings are calculated and separated out from the observed spectral width before estimating ε. It is found that in the lower tropospheric height region ε is in the range from 10 −5.0 to 10 −1.0 m 2 s −3. ε showed significant diurnal variation in the boundary-layer. The larger values of ε, 10 –2.7 m 2 s −3, are noted to be associated with the Convective Boundary-Layer (CBL). The parameter ε is also showing significant seasonal variation. In summer and monsoon seasons the boundary-layer depths are observed up to a height of ∼4.0 km while the same are confined to below 2.0 km in post-monsoon and winter seasons.

Planetary boundary layer and precipitation studies using lower atmospheric wind profiler over tropical India

For the first time in India, an L‐band (1357.5 MHz) lower atmospheric wind profiler (LAWP) has been installed and successfully operated at Gadanki, India, since September 1997. The first results of the accuracy can be given on the basis of about 24‐day intercomparisons between LAWP and mesosphere‐stratosphere‐troposphere radar data. The root‐mean‐square differences (RMS deviation) have been found to range between 1.18 m/s and 1.6 m/s for the wind speed. The two wind profilers compliment each other quite well, considering both the availability and the reliability of the wind measurements. Statistics of the data availability can be shown based on 775 days of data in low mode and about 532 days of data in high mode. The 80% availability of the LAWP was determined with 3.6‐km wind measurements in low mode and 5‐km wind measurements in high mode. LAWP observations show well‐marked planetary boundary layer diurnal variation on clear sunny days. We found that with a few exceptions the drier period has a higher boundary layer compared with the wet period, indicating that in the wet season, most of the net solar radiation evaporated moisture rather than heating the surface and therefore contributed little to buoyant forcing. We classified precipitating clouds into three types: convective, transition, and stratiform. Diurnal and seasonal variation of the occurrence of precipitating cloud systems shows that the precipitation primarily occurs in the afternoon and the convective and transition clouds are most frequent in the summer monsoon, while the occurrence of stratiform clouds is predominant in the winter monsoon.

Lower atmospheric wind profiler at Gadanki, tropical India: Initial results

For the first time at Gadanki, India, an L-band (1357.5 MHz) Lower Atmospheric Wind Profiler (LAWP) has been in operation since August 1997. Gadanki-LAWP provides continuous high-resolution wind measurements in the first few kilometers of the atmosphere and offers excellent opportunity to diagnose convective planetary boundary layer and precipitating cloud systems. To check the reliability winds observed with the Gadanki-LAWP system are compared with the Indian MST radar measurements. Though the echo mechanism is different, the comparison of wind speed shows fairly good agreement. Gadanki-LAWP can provide continuous convective atmospheric boundary layer (CBL) height measurements with very good time resolution (5 minutes or less), allowing for detailed understanding of the growth and fluctuations of the CBL. In this paper we also examine the application of LAWP to the diagnosis and classification of precipitating cloud systems at Gadanki.

Classification of tropical precipitating systems and associated Z‐R relationships

Simultaneous observations of Indian Mesosphere‐Stratosphere‐Troposphere (MST) radar, Lower Atmospheric Wind Profiler (LAWP) and disdrometer, located at Gadanki (13.5°N, 79.2°E), over two seasons are used to derive the Z‐R relationships, of the form Z = ARb, for different types of precipitation and for different seasons. Disdrometer data are classified into three types, convection, transition, and stratiform, based on the variation of the median volume diameter D0 with the rain rate R. The disdrometer classification is verified by comparing with the profilers classification, based on reflectivity (in terms of range corrected signal‐to‐noise ratio), Doppler velocity, spectral width, and vertical air velocity. Overall agreement between the two classification schemes is found to be reasonable. The variations in the coefficient A and the exponent b in the Z‐R relation for the case studies presented here are explained with the help of variations in drop size distribution parameters. From the total data the percentage occurrence of precipitation is found to be 55% stratiform, 9% convective, and 36% transition, whereas the total rainfall is 12, 54, and 34%, respectively. Interestingly, the exponent b (coefficient A) is found to be smaller (larger) in the case of stratiform (convective) precipitation than that in convective (stratiform) precipitation, in contrast to the earlier results. The values of A and b are also derived for different monsoon seasons.