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The present work evaluates eleven existing empirical models to estimate Precipitable Water Vapor ( P W V ) over a high-altitude (4500 m amsl), cold-desert environment. These models are tested extensively and used globally to estimate P W V for low altitude sites (below 1000 m amsl). The moist parameters used in the model are: water vapor scale height ( H c ), dew point temperature ( T d ) and water vapor pressure ( E s 0 ). These moist parameters are derived from surface air temperature and relative humidity measured at high temporal resolution from automated weather station. The performance of these models are examined statistically with observed high-resolution GPS ( G P S P W V ) data over the region (2005–2012). The correlation coefficient (R) between the observed G P S P W V and Model P W V is 0.98 at daily data and varies diurnally from 0.93 to 0.97. Parameterization of moisture parameters were studied in-depth (i.e., 2 h to monthly time scales) using G P S P W V , T d , and E s 0 . The slope of the linear relationships between G P S P W V and T d varies from 0.073°C −1 to 0.106°C −1 (R: 0.83 to 0.97) while G P S P W V and E s 0 varied from 1.688 to 2.209 (R: 0.95 to 0.99) at daily, monthly and diurnal time scales. In addition, the moist parameters for the cold desert, high-altitude environment are examined in-depth at various time scales during 2005–2012. [ABSTRACT FROM AUTHOR]

Integrated precipitable water vapor (PWV) retrieved from Moderate Resolution Imaging Spectro-radiometer (MODIS) in near-infrared channels is examined with the PWV estimated from the Global Positioning System (GPS) data and measured surface temperature and pressure values over Hanle, located at a high-altitude (∼4500 m) trans-Himalayan region. Since the accuracy of MODIS derived PWV over the large elevated topography of the region is not well studied, the present work focus on the validation of MODIS PWV using the GPS data during 2005–2012. The study reveals that MODIS PWV compares well with the GPS PWV data with bias −0.018 cm, root mean square error (RMSE) 0.137 cm and coefficient of determination ( R 2 ) 0.91. The two types of data products are compared on short (daily) and long temporal (monthly-seasonal) scales in order to evaluate the seasonal dependence of PWV. The peak values of PWV from MODIS and GPS data at the site varied from 1.7 to 2.05 cm and 1.2 to 1.4 cm as the daily and the monthly means, respectively, which occurred during August. However, the seasonal peak of PWV occurred during summer as 0.88 and 0.97 cm for MODIS and GPS data, respectively. The present study noticed that about 85% of the total PWV estimated from MODIS as well as GPS data lies below 1.0 cm over the site. The seasonal study of PWV reveals that MODIS data is found to be underestimating the PWV when compared to GPS data with bias −0.095 cm and RMSE 0.215 cm particularly during summer. This is due to dry and high-altitude terrain of Hanle particularly during summer months. However, there are marginal differences (bias varied from 0.007 to 0.017 cm) during the remaining seasons and seasonally R 2 varies from 0.62 to 0.87. GPS PWV exhibits distinct diurnal cycle with minimum in morning as well as in night and peak in the late afternoon (16–18 h) irrespective of the seasons. However, the diurnal cycle is very prominent during summer than the rest of the seasons. [ABSTRACT FROM AUTHOR]

Abstract: Water vapour plays a dominant role in the high-energy thermodynamics of the atmosphere, notably, the genesis of storm systems. However, its distribution is difficult to resolve by conventional means, since water vapour exhibits very high spatial and temporal variability. The growing networks of continuously operating GPS systems, however, offer the possibility of estimating the integrated water vapour (IWV) or, equivalently precipitable water vapour (PW). These estimates constitute critical inputs in operational weather forecasting and fundamental research to model atmospheric storm systems, atmospheric chemistry, and the hydrological cycle. This paper presents the results of IWV estimates from GPS data from continuously operating GPS stations established by C-MMACS at Bangalore, Kodaikanal, Hanle and Shillong over the 3-year period (2001–2003). These are the first results of such an endeavor, towards the study of PW at four different geographical locations in the Indian subcontinent. [Copyright &y& Elsevier]

Precipitable Water Vapor (PWV) is estimated using MODIS (Moderate Resolution Imaging Spectro-radio-meter) Terra level 3 data with daily resolution i. e MOD08_D3 at 64 cGPS (continuous Global Positioning System) stations spatially spread over Indian subcontinent between geodetic latitude 5° to 35° N and geodetic longitude of 70° to 96° E. MODIS-PWV is compared with GPS-PWV estimated at these cGPS stations to check the validity of water vapor retrieved from MODIS data in Indian subcontinent. Correlation coefficient (R2) between daily values of MODIS and GPS water vapor is above 0.9 with RMSE (root mean square error) of 2–5 mm for 22 cGPS in peninsular India, above 0.9 with RMSE of 3–6 mm for 5 cGPS in northeast India and above 0.8 with RMSE of 1–9 mm for 26 cGPS in Himalayas. PWV time series at all the cGPS stations indicated distinct seasonal cycle for both MODIS and GPS PWV with high RMSE (~6 mm) in wet months and low RMSE (~3 mm) during dry months. Taking advantage of broad spatial spread of stations and long span of data, model for spatial variability of GPS-PWV for Indian subcontinent is proposed. Inter-annual and seasonal variability of GPS-PWV is discussed in detail for peninsular India, northeast India and Himalayas. • Validation of MODIS-PWV using long data span at 64cGPS sites for Indian region. • MODIS-PWV has high RMSE, bias for coastal, islands and varying topography regions. • MODIS data fails to capture the seasonal variability of PWV for Indian sub-continent. • Spatial variability function of GPS-PWV is given for Indian Sub-continent. • Relation between the seasonal variability of PWV and temperature variation is given. [ABSTRACT FROM AUTHOR]

The present work reports atmospheric opacity at 220 GHz over Indian Astronomical Observatory (IAO)-Hanle during 2006 to 2018. The opacity data were derived from the radiometric measurement of sky-brightness temperature as a function of zenith angle for every 10 min during day and night. Since the operating frequency range is not completely opaque during rainfall or cloudy atmosphere, observations are performed even during rainfall or cloudy sky conditions. The minimum opacities observed at the site varied from 0.06-0.07 at 1st quartile and 0.08-0.09 at 2nd quartile during December-January. Opacity at Hanle is linearly correlated with high temporal resolution GPS (Global Positioning System) Precipitable Water Vapor (PWV) with a correlation coefficient of about 0.8. The observed median opacity at Hanle has increased by 44% during the best observing months (October–March) and 24% over the annual data (October-September) with reference to the opacity observed during 2000–2003. Such increasing opacity trends are apparently due to effects of the dynamics of the regional and global hydrological cycle. In order to assess the impacts of the regional and global hydrological cycle, PWV obtained from AErosol RObotic NETwork (AERONET), satellite and reanalysis data were studied at nine high-altitude astronomical observatories spread spatially across the globe such as Atacama desert in Chile, Mauna Loa Observatory in Hawaii, Hanle and Merak in India, Ali and Yangbajing Observatories in Tibet, LLAMA in Argentina, and Dome A and Dome C in the Antarctic Plateau during 2003-2018. On an average, PWV trend over Atacama desert is increasing by 0.01 to 0.03 mm per year and at IAO-Hanle, Merak and Ali by 0.01 to 0.05 mm per year, indicating non uniform dynamic hydrological cycles. Interestingly, there is no noticeable PWV trend for the sites located in the Antarctic Plateau. During the four best observing months, PWV observed at Hanle, Merak and Ali sites have values lower than the Mauna Loa observatory by 0.14 mm and 0.56 mm at 1st and 2nd quartiles, respectively. • Median opacities at Hanle during 2006–2018 varied from 0.08–0.09 in winter. • Increasing opacity trends of 24% are noticed at Hanle using multi-year data sets. • Median precipitable water vapor (PWV) at Merak and Hanle varied from 2.16–2.23 mm. • Increasing opacity trends are attributed to increasing PWV of 0.01–0.05 mm yr-1. • Increasing PWV (0.01–0.03 mm yr-1) is observed at driest site in Atacama desert. [ABSTRACT FROM AUTHOR]