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Tree-ring analysis over western Himalaya and its long-term association with vapor pressure and potential evapotranspiration
No full textMulti species tree-ring chronologies of the western Himalaya revealed strong significant negative relationship with potential evapotranspiration (PET) and vapor pressure (VP), and positive with moisture index (MI) and Palmer Drought Severity Index (PDSI) during spring season (March to May). The preliminary study showed that the MI and PDSI particularly in spring season might have a large scale positive association in developing of annual ring-width patterns, whereas PET and VP during the season are found not to be conducive for the trees growth. PET and VP from the beginning of the year 1917 showed strong influence on tree growth. High and low PET/VP might be associated with low and high MI/PDSI of the region. Extremely narrow ring width indices were observed in the year of 1921, 1941, 1953, 1954 and 1985 at most of the tree sites which are under the severe moisture stress condition due to extremely high PET and VP of the region. Also, extremely low PET and VP were found during 1917, 1933 and 1982, reflecting ring-width index above the normal due to enough moisture supply. Thus, the released and suppressed tree growth over the region is probably linked with the high and low MI/PDSI of the region. Loss or accumulation of soil moisture of the region might be precondition before the starting of growing season of the trees. The recent observation also suggests a weakening of VP and PET's influence on tree growth during recent few decades as compared to early period in sliding 31-years windows over western Himalaya. Correlation analysis of PET with MI and VP as well as PDSI for the period 1902-2002 during spring season indicated statistically strong correlation ( r= -0.53, 0.82, -0.50) respectively which is highly significant at 0.01 level
Temperature analysis over southwest Iran: Trends and projections
No full textThe present study intends to show the effect of climate change on trends and patterns of temperature over the southwestern part of Iran. The research has been divided into two parts. The first part consists of an analysis of the temperature trends of mean temperature (TM), maximum temperature (TMAX), and minimum temperature (TMIN) over 39 stations in the study region for the period 1950-2007. The trends in these parameters were detected by linear regression, and significance was tested by t test. Mann-Kendall rank test (MK test) was also employed to confirm the results. The second part of the research involved future projection of temperature based on four models. The models used were Centre National de Recherches Meteorologiques, European Center Hamburg Model, Model for Interdisciplinary Research on Climate, and UK Meteorological Office. Temperature projections were done under B1 and A1B emissions scenarios. The analysis of temperature trends revealed a significant increase during summer and spring seasons. TMAX was stable than TMIN and TM, and winter was stable as compared with summer, spring, and autumn seasons. Results of modeling showed that temperature may increase between 1.69 and 6.88 °C by 2100 in the study area. Summer temperatures may increase with higher rates than spring, winter, and autumn temperatures
Improved simulation of Indian summer monsoon in latest NCEP climate forecast system free run
No full textSimulation of Indian summer monsoon features by latest coupled model of National Centers for Environmental Prediction (NCEPs) Climate Forecast System version 2 (CFSv2) is attempted in its long run. Improvements in the simulation of Indian summer monsoon as compared with previous version (CFSv1) is accessed and areas which still require considerable refinements are introduced. It is found that, spatial pattern of seasonal mean rainfall and wind circulations are more realistic in CFSv2 as compared with CFSv1. Variance and northward propagation of intraseasonal oscillation (ISO), which also contribute to the seasonal mean rainfall are remarkably improved. However, the central Indian dry bias still persists and amplified. Pervasive cold bias in surface (2m air temperature) as well as in the whole troposphere is further increased in CFSv2. These cold biases may be partly attributed to the lack of model's ability to realistically simulate the ratio of convective and stratiform rainfall. Sea-surface temperature (SST) over the Indian Ocean is underestimated in CFSv2. However, CFSv1 shows east-west dipole structure in the bias. The teleconnection of El Nino Southern Oscillation (ENSO) and Indian summer monsoon rainfall (ISMR) in terms of Niño3 SST and monsoon rainfall correlation is more realistic in the latest version of the model. Overall, there are substantial improvements in CFSv2 as compared with CFSv1, but it has to evolve further to realistically simulate the mean and variability of ISMR
Increased frequency of extreme Indian ocean dipole events due to greenhouse warming
No full textThe Indian Ocean dipole is a prominent mode of coupled ocean-atmosphere variability, affecting the lives of millions of people in Indian Ocean rim countries. In its positive phase, sea surface temperatures are lower than normal off the Sumatra-Java coast, but higher in the western tropical Indian Ocean. During the extreme positive-IOD (pIOD) events of 1961, 1994 and 1997, the eastern cooling strengthened and extended westward along the equatorial Indian Ocean through strong reversal of both the mean westerly winds and the associated eastward-flowing upper ocean currents. This created anomalously dry conditions from the eastern to the central Indian Ocean along the Equator and atmospheric convergence farther west, leading to catastrophic floods in eastern tropical African countries but devastating droughts in eastern Indian Ocean rim countries. Despite these serious consequences, the response of pIOD events to greenhouse warming is unknown. Here, using an ensemble of climate models forced by a scenario of high greenhouse gas emissions (Representative Concentration Pathway 8.5), we project that the frequency of extreme pIOD events will increase by almost a factor of three, from one event every 17.3 years over the twentieth century to one event every 6.3 years over the twenty-first century. We find that a mean state change-with weakening of both equatorial westerly winds and eastward oceanic currents in association with a faster warming in the western than the eastern equatorial Indian Ocean-facilitates more frequent occurrences of wind and oceanic current reversal. This leads to more frequent extreme pIOD events, suggesting an increasing frequency of extreme climate and weather events in regions affected by the pIOD
Climatic response of various tree ring parameters of fir (Abies pindrow) from Chandanwadi in Jammu and Kashmir, western Himalaya, India
Get PDFTotal ring width (TRW) and earlywood width (ERW) of fir (Abies pindrow) compared to latewood width (LRW) are strongly correlated with Palmer Drought Severity Index (PDSI) during summer season (March to October). Correlation coefficients for the period 1876-1948 between PDSI and TRW as well as ERW are 0.43 and 0.50 respectively, which is found to be significant at 0.01 level. Thereafter, their relationship weakened as temperature changed over the region, whereas maximum latewood density (MXD) reveals significant negative association with PDSI during summer season. Moreover, monthly mean, maximum and minimum temperatures during August to September of the region indicate significant positive response with MXD. Correlation coefficients of MXD with mean, maximum and minimum temperatures are 0.60, 0.61 and 0.51 respectively, which is significant at 0.01 level. There is also high temporal stability in the relationship between MXD and temperature from 1916 onwards over the region
Simulation of severe thunder storm event: A case study over Pune, India
No full textNumerical simulation of a typical tropical thunder storm event at Pune (18.53°N, 73.85°E), India, has been performed using the three nested domain configuration of Weather Research and Forecasting-Advanced Research Weather Model (version 3.2). The model simulations have been compared with observations. Sensitivity to cumulus parameterization schemes, namely Betts-Miller (BM), Grell-Devenyi (GD), and Kain-Fritsch (KF), for simulation of vertical structure and time evolution of weather parameters has been evaluated using observations from automatic weather station and global positioning system radiosonde ascents. Comparison of spatial distribution of 24-h accumulated rain with Tropical Rainfall Measuring Mission data shows that BM scheme could simulate better rain than GD and KF schemes. The BM scheme could well simulate the development of storm and heavy rain as it could generate sufficiently humid and deep layer in the lower and middle atmosphere, along with co-existence of updrafts and downdrafts and frozen hydrometeors at the middle level and rain water near the surface
Addendum to: "A global assessment of precipitation chemistry and deposition of sulfur, nitrogen, sea salt, base cations, organic acids, acidity and pH, and phosphorus"
No full textThe screening of measurement-based precipitation chemistry and wet and dry deposition data involved detailed assessments of site representativeness, sampling protocols, laboratory analyses, data completeness and overall measurement qualit
Diurnal and seasonal characteristics of aerosol ionic constituents over an urban location in Western India: Secondary aerosol formation and meteorological influence
Get PDFWater-soluble ionic constituents (Cl–, NO3–, SO42–, Na+, NH4+, K+, Mg2+ and Ca2+) of PM2.5 were measured using Ambient Ion Monitor coupled-to Ion Chromatography (AIM-IC) with a time resolution of one hour at Ahmedabad (an urban location in a semi-arid region of western India) during summer and winter to study the diurnal and seasonal variations. Maximum abundances of most of the species were observed during afternoon hours in summer, whereas minimum concentrations were found during winter at the same local time. During summer, the concentration levels of most of the constituents in a diurnal cycle are largely influenced by variations in the ambient relative humidity. During winter, the emission strength and boundary layer dynamics impact the diurnal cycle. Secondary inorganic species like NH4+, NO3– and SO42– exhibit significant differences in their relative abundances during winter and summer. Four factors have been derived by Positive Matrix Factorization (PMF) analysis of the water-soluble ionic constituents. These are secondary, sea-salt, mineral dust sources, while the fourth factor is associated with K+, which is likely to be due to emissions related to biomass burnin
Corrigendum to "Boundary layer jet on the lee side of Western Ghats during southwest monsoon as revealed by high resolution sodar winds"
No full textWaves off Gopalpur, northern Bay of Bengal during Cyclone Phailin
Get PDFThe wave statistical parameters during Cyclone Phailin which crossed the northern Bay of Bengal are described based on the Directional Waverider buoy-measured wave data from 8 to 13 October 2013. On 12 October 2013, the cyclone passed within 70 km of the Waverider buoy location with a wind speed of 59.2 m sg-1 (115 knots), and during this period, a maximum significant wave height of 7.3 m and a maximum wave height of 13.5 m were measured at 50 m water depth. Eight freak wave events are observed during the study period. The ratio of the maximum wave height to significant wave height recorded is found to be higher than the theoretical value and the ratio of the crest height to wave height during the cyclone was 0.6 to 0.7. The characteristics of the wave spectra before and after the cyclone is studied and found that the high-frequency face of the wave spectrum is proportional to f-3 before the cyclone and is between f-4 and f -5 during the cyclone period