GPS Water Vapor and Its Comparison with Radiosonde and ERA-Interim Data in Algeria

Remote sensing of atmospheric water vapor using global positioning system（GPS） data has become an effective tool in meteorology,weather forecasting and climate research. This paper presents the estimation of precipitable water（PW）from GPS observations and meteorological data in Algeria,over three stations located at Algiers,Bechar and Tamanrasset.The objective of this study is to analyze the sensitivity of the GPS PW estimates for the three sites to the weighted mean temperature（T;）,obtained separately from two types of T;–T;regression [one general,and one developed specifically for Algeria（T;stands for surface temperature）],and calculated directly from ERA-Interim data. The results show that the differences in T;are of the order of 18 K,producing differences of 2.01 mm in the final evaluation of PW. A good agreement is found between GPS-PW and PW calculated from radiosondes,with a small mean difference with Vaisala radiosondes.A comparison between GPS and ERA-Interim shows a large difference（4 mm） in the highlands region. This difference is possibly due to the topography. These first results are encouraging,in particular for meteorological applications in this region,with good hope to extend our dataset analysis to a more complete,nationwide coverage over Algeria.

Correlation between Atmospheric Water Vapor and Diurnal Temperature Range over China

Diurnal temperature range （DTR） is an im- portant measure in studies of climate change and variability. The changes of DTR in different regions are affected by many different factors. In this study, the degree of correlation between the DTR and atmospheric precipitable water （PW） over China is explored using newly homogenized surface weather and sounding observations. The results show that PW changes broadly reflect the geographic patterns of DTR long-term trends over most of China during the period 1970-2012, with significant anticorrelations of trend patterns between the DTR and PW, especially over those regions with higher magnitude DTR trends. PW can largely explain about 40% or more （re 0.40） of the DTR changes, with a d（PW）/d（DTR） slope of -2% to -10% K^-1 over most of northwestern and southeastern China, despite certain seasonal dependencies. For China as whole, the significant anticorrelations between the DTR and PW anomalies range from -0.42 to -0.75, with a d（PW）/d（DTR） slope of-6% to -11% K^-1. This implies that long-term DTR changes are likely to be associated with opposite PW changes, approximately following the Clausius-Clapeyron equation. Furthermore, the relationship is more significant in the warm season than in the cold season. Thus, it is possible that PW can be considered as one potential factor when exploring long-term DTR changes over China. It should be noted that the present study has a largely statistical focus and that the underlying physical processes should therefore be examined in future work.

Variations in stable hydrogen and oxygen isotopes in atmospheric water vapor in the marine boundary layer across a wide latitude range

The newly-developed cavity ring-down laser absorption spectroscopy analyzer with special calibration protocols has enabled the direct measurement of atmospheric vapor isotopes at high spatial and temporal resolution. This paper presents real-time hydrogen and oxygen stable isotope data for atmospheric water vapor above the sea surface, over a wide range of latitudes spanning from 38°N to 69°S. Our results showed relatively higher values of 8180 and 82H in the subtropical regions than those in the tropical and high latitude regions, and also a notable decreasing trend in the Antarctic coastal region. By combining the hydrogen and oxygen isotope data with meteoric water line and backward trajectory model analysis, we explored the kinetic fractionation caused by subsiding air masses and related saturated vapor pressure in the subtropics, and the evaporation-driven kinetic fractionation in the Antarctic region. Simultaneous observations of meteorological and marine variables were used to interpret the isotopic composition characteristics and influential factors, indicating that d-excess is negatively correlated with humidity across a wide range of latitudes and weather conditions worldwide. Coincident with previous studies, d-excess is also positively correlated with sea surface temperature and air temperature （Tair）, with greater sensitivity to Tair. Thus, atmospheric vapor isotopes measured with high accuracy and good spatial- temporal resolution could act as informative tracers for exploring the water cycle at different regional scales. Such monitoring efforts should be undertaken over a longer time period and in different regions of the world.

Analysis of Precipitation Resource and Weather Modification Potential in Anyang

Using ground water vapor pressure and precipitation data at four times of one day during 1985- 2014 in each county（ city） of Anyang,precipitable water at each station was calculated,and temporal-spatial distribution of atmospheric maximum precipitable water and its change trend over the years in the city were analyzed. Results showed that atmospheric maximum precipitable water in Anyang City had the characteristics of summer far more than winter,autumn slightly higher than spring,west and south more,and east and north less,and presented the increasing trend year by year. We further analyzed the characteristic of monthly rainfall enhancement potential in each county,and mean in whole year was 80%. In spring and winter,rainfall enhancement potential in the west was bigger than east,while rainfall enhancement potential in the east was bigger than west in summer and autumn. The research provides reference basis for rationally carrying out artificial rainfall work,which could effectively ease uneven temporal-spatial distribution problem of water resource in Anyang City.

Short-term variations of vapor isotope ratios re- veal the influence of atmospheric processes

Stable isotopes of atmospheric water vapor reveal rich information on water movement and phase changes in the atmosphere. Here we presented two nearly continuous time-series of δD and δ18O of atmospheric water vapor （δv） measured at hourly intervals in surface air in Beijing and above a winter wheat canopy in Shijiazhuang using in-situ measurement technique. During the precipitation events, the δv values in both Beijing and Shijiazhuang were in the state of equilibrium with precipitation water, revealing the influence of precipitation processes. However, the δv departures from the equilibrium state were positively correlated with local relative humidity. Note that the δv tended to enrich in Beijing, but deplete in Shijiazhuang during the precipitation events, which mainly resulted from the influence of transpiration processes that enriched the δv in Shijiazhuang. On seasonal time-scale, the δv values were log-linear functions of water vapor mixing ratios in both Beijing and Shijiazhuang. The water vapor mixing ratio was an excellent predictor of the δv by the Rayleigh distillation mechanisms, indicating that air mass advection could also play an important role in determining the δv. On a diurnal time-scale, the δv reached the minimum in the early afternoon hours in Beijing which was closely related to the atmospheric processes of boundary layer entrainment. During the peak of growing season of winter wheat, however, the δv reached the minimum in the early morning, and increased gradually through the daytime, and reached the maximum in the late afternoon, which was responsible by the interaction between boundary layer entrainment and the local atmospheric processes, such as transpiration and dew formation. This study has the implications for the important role of vegetation in determining the surface δv and highlights the need to conduct δv measurement on short-term （e.g. diurnal） time scales.

Decadal Variability of Extreme Precipitation Days over Northwest China from 1963 to 2012

Daily precipitation data from 153 meteorological stations over Northwest China during summer from 1963 to 2012 were selected to analyze the spatiotemporal distribution of extreme summer precipitation frequency.The results show that the extreme precipitation frequency was regional dependent.Southern Gansu,northern Qinghai,and southern Shaanxi provinces exhibited a high extreme precipitation frequency and were prone to abrupt changes in the frequency.Northwest China was further divided into three sub-regions（northern,central,and southern） based on cluster analysis of the 50-yr extreme precipitation frequency series for each meteorological station.The extreme precipitation frequency changes were manifested in the northern region during the late 1970 s and in the central region from the end of the 1980 s to the 1990 s.The southern region fluctuated on a timescale of quasi-10 yr.This study also explored the mechanism of changes in extreme precipitation frequency.The results demonstrate that stratification stability,atmospheric water vapor content,and upward motion all affected the changes in extreme precipitation frequency.