R.T. Waghmare

Measurements of carbon dioxide and heat fluxes during monsoon-2011 season over rural site of India by eddy covariance technique

An increase in carbon dioxide (CO2) concentrations in the atmosphere due to anthropogenic activities is responsible for global warming and hence in recent years, CO2 measurement network has expanded globally. In the monsoon season (July–September) of year 2011, we carried out measurements of CO2 and water vapour (H2O) concentrations along with wind and air temperature over a tropical site in south-east India having rural topography. To collect these observations, the instrumentations used were the sonic anemometer for wind and temperature, and the open path H2O/CO2 infrared gas analyzer for CO2 and H2O concentrations. Using these observations, we explored the diurnal variability of CO2 flux along with sensible and latent heat. The CO2 flux was positive during night-time and negative during daytime and in phase with convective instability. The CO2 flux relationships with the meteorological parameters such as wind speed, temperature and heat fluxes have been analysed. The seasonal (monsoon) half hour mean of CO2 flux which was −3.55xa0μmol mu2009−u20092xa0su2009−u20091 indicated the experimental site as a CO2 sink region (net seasonal uptake). An increase in CO2 concentrations during weekends was not observed due to unavailability of heavy vehicular traffic.

Relationship between aerosol and lightning over Indo-Gangetic Plain (IGP), India

The relationship between aerosol and lightning over the Indo-Gangetic Plain (IGP), India has been evaluated by utilising aerosol optical depth (AOD), cloud droplet effective radius and cloud fraction from Moderate Resolution Imaging Spectroradiometer. Lightning flashes have been observed by the lightning Imaging sensor on the board of Tropical Rainfall and Measuring Mission and humidity from modern-era retrospective-analysis for research and applications for the period of 2001–2012. In this study, the role of aerosol in lightning generation over the north-west sector of IGP has been revealed. It is found that lightning activity increases (decreases) with increasing aerosols during normal (deficient) monsoon rainfall years. However, lightning increases with increasing aerosol during deficient rainfall years when the average value of AOD is less than 0.88. We have found that during deficient rainfall years the moisture content of the atmosphere and cloud fraction is smaller than that during the years with normal or excess monsoon rainfall over the north-west IGP. Over the north-east Bay of Bengal and its adjoining region the variations of moisture and cloud fraction between the deficient and normal rainfall years are minimal. We have found that the occurrence of the lightning over this region is primarily due to its topography and localised circulation. The warm-dry air approaching from north-west converges with moist air emanating from the Bay of Bengal causing instability that creates an environment for deep convective cloud and lightning. The relationship between lightning and aerosol is stronger over the north-west sector of IGP than the north-east, whereas it is moderate over the central IGP. We conclude that aerosol is playing a major role in lightning activity over the north-west sector of IGP, but, local meteorological conditions such as convergences of dry and moist air is the principal cause of lightning over the north-east sector of IGP. In addition, atmospheric humidity also plays an important role in regulating the effect of aerosol on the microphysical properties of clouds over IGP region.

Evaluation of Noah-LSM for soil hydrology parameters in the Indian summer monsoon conditions

The micrometeorological observations, collected over a station in Ranchi (23°45′N, 85°30′E) which is under the monsoon trough region of India, were used in the Noah-LSM (NCEP, OSU, Air Force and Office of Hydrology Land Surface Model) to investigate the model performance in wet (2009 and 2011) and dry (2010) conditions during the south-west summer monsoon season. With this analysis, it is seen that the Noah-LSM has simulated the diurnal cycle of heat fluxes (sensible and ground) reasonably. The simulated heat fluxes were compared with its direct measurements by sonic anemometer and soil heat flux plate. The net radiation and sensible heat flux are simulated well by the model, but the simulation of ground heat flux was found to be poor in both dry as well as wet conditions. The soil temperature simulations were also found to be poor in 0–5- and 5–10-cm layers compared to other deeper layers. The observations were also correlated with the Modern Era Retrospective-analysis for Research and Applications (MERRA) data. The correlation between the observations and ground heat flux was better in MERRA dataset than that of the Noah-LSM simulation.

Noah-lsm simulation on various soil textures in tropical semi-arid regions

Abstract Land Surface Processes Experiment was conducted in the year 1997 in which land surface observations were collected over a tropical semi-arid region of Gujarat, India. Using these observations, Noah Land Surface Model version 2.7.1 (Noah-LSM) has been tested in the wet and dry surface conditions for four test sites, viz., Anand (22°35′ N, 72°55′ E), Derol (22°40′ N, 73°45′ E), Arnej (22°40′ N, 72°15′ E), and Khandha (22°02′ N, 73°11′ E) having different soil texture (sandy loam and clay). Model simulations for net radiation, skin temperature, and soil temperature at various depths were compared with observations. Initial results of soil and surface temperature showed good agreement for clay soil texture compared with sandy loam textures during dry periods. In contrast, for wet periods. Contrastingly, for wet periods, the net radiation and skin temperature showed better agreement for sandy loam textures than for clay textured soils. The model simulation was repeated for the sandy loam soil texture soil during dry period and for the clay texture soil during the wet period by replacing the model estimated soil thermal conductivity by the annual mean soil thermal conductivity of test stations. The results were improved for sandy loam texture but remain unchanged for clay texture. Comparison of simulated and observed parameters shows good correlation, high index of agreement, and low error. Overall, the results simulated by Noah-LSM for both soil textures are comparable with the observations.

Carbon dioxide and water vapour characteristics on the west coast of Arabian Sea during Indian summer monsoon

Carbon dioxide, water vapour, air temperature and wind measurements at 10xa0Hz sampling rate were carried out over the coast of Arabian Sea, Goa (15°21′N, 73°51′E) in India. These observations were collected, in association with the surface layer turbulent parameters for the Arabian Sea Monsoon Experiment (ARMEX). In the summer monsoon period, concentration of CO2 was in the range of 550–790xa0mgxa0mu2009−u20093 whereas the water vapour was in the range of 17.5–24.5xa0g mu2009−u20093. The Fast Fourier Transform (FFT) analysis has been performed on these observations to investigate the spectral behaviour of CO2 and water vapour. The relation between CO2 and water vapour on various atmospheric scales has been proposed. CO2 and water vapour observations confirmed the existence of periodicities of large (11, 8xa0days), meso (5xa0days) and micrometeorological (20xa0min) scales.

Cloud condensation nuclei over the Bay of Bengal during the Indian summer monsoon

The first measurements of cloud condensation nuclei (CCN) at five supersaturations were carried out onboard the research vessel “Sagar Kanya” (cruise SK-296) from the south to the head-bay of the Bay of Bengal as part of the Continental Tropical Convergence Zone (CTCZ) Project during the Indian summer monsoon of 2012. In this paper, we assess the diurnal variation in CCN distributions at supersaturations from 0.2% to 1% (in steps of 0.2%) and the power-law fit at supersaturation of 1%. The diurnal pattern shows peaks in CCN concentration (NCCN) at supersaturations from 0.2% to 1% between 0600 and 0700 LST (local standard time, UTC+0530), with relatively low concentrations between 1200 and 1400 LST, followed by a peak at around 1800 LST. The power-law fit for the CCN distribution at different supersaturation levels relates the empirical exponent (k) of supersaturation (%) and the NCCN at a supersaturation of 1%. The NCCN at a supersaturation of 0.4% is observed to vary from 702 cm−3 to 1289 cm−3, with a mean of 961±161 cm−3 (95% confidence interval), representing the CCN activity of marine air masses. Whereas, the mean NCCN of 1628±193 cm−3 at a supersaturation of 1% is higher than anticipated for the marine background. When the number of CCN spectra is 1293, the value of k is 0.57±0.03 (99% confidence interval) and its probability distribution shows cumulative counts significant at k ≈ 0.55±0.25. The results are found to be better at representing the features of the marine environment (103 cm−3 and k ≈ 0.5) and useful for validating CCN closure studies for Indian sea regions.摘 要作为大陆热带辐合带 (CTCZ) 计划的组成部分, 利用“萨加尔坎亚”科考船(编号SK-296)船载仪器对 2012 年印度夏季风期间孟加拉湾南部到前端地区五种过饱和度下的云凝结核 (CCN) 进行了首次观测. 本文分析了过饱和度从 0.2%到 1%(间隔为 0.2%) 下的 CCN 日变化特征和在 1%过饱和度下使用幂函数拟合的 CCN 谱分布. 日变化特征显示过饱和度从 0.2%到 1%时 CCN数浓度(NCCN) 在 0600 到 0700 LST(当地时间, 协调世界时 +0530)出现峰值, 接着在 1200 到 1400 LST 出现相对低值, 然后在 1800 LST 左右又出现峰值. 不同过饱和度下幂函数拟合的 CCN 谱分布依赖于和过饱和(%)相关的经验参数 k 以及 1%过饱和度下的 CCN 数浓度. 过饱和度为 0.4%时 CCN 数浓度的变化范围为 702 cm−3 到 1289 cm−3, 平均值为 961 ± 161 cm−3(95%置信区间), 代表了海洋性 CCN 特征. 然而当过饱和度为 1%时, 1628 ± 193 cm−3 的平均 NCCN 高于预期的海洋背景 CCN 数浓度. 当 CCN 谱的参数 C 值是 1293 时, 参数 k 值为 0.57 ± 0.03(99%置信区间)并且其概率分布的累计频数显著出现在 k ≈ 0.55 ± 0.25. 上述结果能够更好的代表海洋性 CCN 特征(C=103 cm−3 和 k ≈ 0.5)并且有助于验证印度洋地区的 CCN 闭合结果.

The influence of wind speed on surface layer stability and turbulent fluxes over southern Indian peninsula station

Surface to atmosphere exchange has received much attention in numerical weather prediction models. This exchange is defined by turbulent parameters such as frictional velocity, drag coefficient and heat fluxes, which have to be derived experimentally from high-frequency observations. High-frequency measurements of wind speed, air temperature and water vapour mixing ratio (eddy covariance measurements), were made during the Integrated Ground Observation Campaign (IGOC) of Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) at Mahabubnagar, India (16∘44′N, 77∘59′E) in the south-west monsoon season. Using these observations, an attempt was made to investigate the behaviour of the turbulent parameters, mentioned above, with respect to wind speed. We found that the surface layer stability derived from the Monin–Obukhov length scale, is well depicted by the magnitude of wind speed, i.e., the atmospheric boundary layer was under unstable regime for wind speeds >4 m s−1; under stable regime for wind speeds <2 m s−1 and under neutral regime for wind speeds in the range of 2–3 m s−1. All the three stability regimes were mixed for wind speeds 3–4 m s−1. The drag coefficient shows scatter variation with wind speed in stable as well as unstable conditions.