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 10 Hz 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 CO 2 was in the range of 550-790 mg m -3 whereas the water vapour was in the range of 17.5-24.5 g m -3. The Fast Fourier Transform (FFT) analysis has been performed on these observations to investigate the spectral behaviour of CO 2 and water vapour. The relation between CO 2 and water vapour on various atmospheric scales has been proposed. CO 2 and water vapour observations confirmed the existence of periodicities of large (11, 8 days), meso (5 days) and micrometeorological (20 min) scales

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 southeast 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 -3.55 μmol m-2 s-1 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

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

Giant Anharmonic Phonon Scattering in PbTe

Understanding the microscopic processes affecting the bulk thermal conductivity is crucial to develop more efficient thermoelectric materials. PbTe is currently one of the leading thermoelectric materials, largely thanks to its low thermal conductivity. However, the origin of this low thermal conductivity in a simple rocksalt structure has so far been elusive. Using a combination of inelastic neutron scattering measurements and first-principles computations of the phonons, we identify a strong anharmonic coupling between the ferroelectric transverse optic (TO) mode and the longitudinal acoustic (LA) modes in PbTe. This interaction extends over a large portion of reciprocal space, and directly affects the heat-carrying LA phonons. The LA-TO anharmonic coupling is likely to play a central role in explaining the low thermal conductivity of PbTe. The present results provide a microscopic picture of why many good thermoelectric materials are found near a lattice instability of the ferroelectric type

Oscillation of wind temperature humidity in the atmospheric surface layer over tropical semi-arid stations

Analysis of wind, air temperature, humidity and rainfall data from Land Surface Processes Experiment (LASPEX) in the surface layer at Anand (22°35′N, 72°55′E) and Khandha (22°02′N, 73°11′E) during January to December 1997 is presented. Wind and temperature at various levels showed prominent diurnal variation. Progression of daily wind and temperature revealed the intra-seasonal, quasi-biweekly and 6–9 day oscillations indicated large-scale convection, transport of heat and water vapor from Arabian Sea towards these stations.Power spectrum of wind and humidity corroborated the planetary scale Madden–Julian oscillation in the surface layer. Periodic oscillations of 21, 6–9, 1 day and 12 h were prominent in the spectrum of all variables. Low-frequency spectral peaks showed the energy in wind is 2–3 times higher over Khandha than at Anand whereas temperature is 3 times higher at Anand than Khandha

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

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. Copyrigh

Planetary Boundary Layer and aerosol interactions over the Indian sub-continent

Aerosols, both natural as well as anthropogenic, affect the radiative forcing of EarthU+05F3s climate and reduce surface albedo. The Planetary Boundary Layer (PBL) height, which depends upon surface heat budget, is analyzed considering the increase in green house gases (GHGs) from pre-industrial to post-industrial era. The PBL climatology shows deeper PBL during pre-monsoon and summer monsoon seasons as compared to post-monsoon and winter. The PBL height has decreased in post-industrial decade compared to pre-industrial decade. The PBL height reduction is due to increasing aerosol and GHGsU+05F3 concentrations in the recent decades, which causes surface warming and upper tropospheric cooling. Similarly, due to higher loading of the volcanic aerosol injected from the low latitude eruptions, the atmospheric circulation has been affected

Planetary Boundary Layer height over the Indian subcontinent during extreme monsoon years

Planetary Boundary Layer (PBL) plays an important role in the regional monsoon circulation by exchanging heat and moisture between the earth surface and free atmosphere. However, PBL climatology over the Indian sub-continent in the context of extreme monsoon conditions is not available for its use in the regional climate models. In this study, a large-scale seasonal feature of PBL height over the Indian sub-continent is explored with 40 years (1961-2000) ERA-40 reanalysis data. The variations in the PBL height associated with excess and deficient monsoons over India are examined. The seasonal climatology showed higher PBL height during pre-monsoon (spring) and monsoon seasons as compared to post-monsoon and winter. For the extreme monsoon situations, PBL over the north-west (NW) India has greatly reciprocated. Over the NW India, during deficient monsoon years, composite anomalies of the PBL are observed to be negative indicating large reduction in PBL. Whereas during excess monsoon years, observed positive anomalies suggest increase in the PBL. During excess (deficient) monsoon years, the convection and the LLJ are found to be stronger (weaker) associated with the higher (lower) PBL height

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

Pre-monsoon/monsoon thunderstorm characteristics over Pune-An investigation using Doppler Sodar observations

Doppler sodar observations of three dimensional (3D) wind fields and thermal structure of convective boundary layer (CBL) on a few thunderstorm days of 2009 during pre-monsoon (May and June; June due to delayed arrival of monsoon over Pune) and monsoon (July and August) are analyzed. They reveal the typical signatures of wind fields for the late afternoon thunderstorm (TS) such as deceleration of winds with or without change in direction leading to convergence a few minutes (∼15–30 min) prior to the onset of TS. Pre-monsoon TS are characterized by broad updrafts and narrow downdrafts in CBL in contrast to the narrow updrafts and broad downdrafts of a normal day (i.e. No-TS day). Mean vertical velocity averaged over CBL period shows net updraft on TS days and net downdraft on No-TS day for the pre-monsoon cases. Similarly calm winds are observed in the CBL on TS-days that support enhanced free convection. During the monsoon period updrafts are observed on both TS and No-TS days with higher values on TS days in comparison, due to the dominance of large-scale monsoon flow over local convection. Relatively higher turbulence kinetic energy (TKE) in CBL is observed on all TS days. Analysis shows that TKE maximum for the day is attained about 1.5–2.0 h prior to the onset of afternoon TS. Mixed-layer depth, determined from TKE profile, is higher than lifting condensation level (LCL) on TS days in May and June indicating saturation of air parcels in updrafts