Trends Of Precipitable Water Research Articles

Precipitable Water Content Climatology over Poland

In this work, the high-resolution spatial and temporal variability of precipitable water (PW) over Poland is presented. PW is one of the key parameters of the atmosphere taken into account in thermodynamic and radiation models. The daily PW values from years 2001–2010, calculated with the use of the WRF model, were compared with PW from soundings. The WRF modeled PW is in close agreement with measurements for the whole column of the troposphere and for individual levels: below 1.5 km, 1.5–3 km, 3–6 km and 6–10 km. The best agreement is observed in the lower part of the troposphere, especially for winter months. At the levels of 1.5 km to 10 km, the WRF model overestimates the PW values throughout the year, whereas up to 1.5 km PW is underestimated. The study shows an increasing trend of PW annual values between 1983 and 2010, but the trend is statistically insignificant. A significant positive trend with a high Sen’s slope is observed for the summer season up to 3 km in the troposphere, along with a significant negative tendency for spring. The trends in PW over Poland and Central Europe identified in this study contribute to the ongoing discussion on the observed climate changes.

Corrections of Radiosonde‐Based Precipitable Water Using Ground‐Based GPS and Applications on Historical Radiosonde Data Over China

AbstractThe usage of radiosonde humidity data in climate studies and atmospheric reanalysis has been greatly hampered by the inhomogeneity issue mainly caused by radiosonde sensor changes. In this work, high‐quality precipitable water (PW) products derived from a national Global Positioning System (GPS) network in China covering the period from 1999 to 2015 were used to quantify errors in radiosonde‐derived PW products for different radiosonde types. Correlations between PW biases and factors including the station location, mean PW, weighted mean temperature (Tm), and solar elevation angle were carefully analyzed. Biases in PW products derived from the mechanical radiosondes (GZZ2, used at most stations before 2001) show strong correlations with the station elevation and Tm, and a PW correction model was then developed. For GTS1 and GTS1‐1 (widely used in current operational system), due to the unobvious correlations between PW biases and these factors, corrections were estimated as mean values of PW biases at all collocated stations. For GTS1‐2, GTS2(U)‐1, and TD2‐A (used at a few stations), subject to insufficient GPS‐radiosonde collocated stations, they are left uncorrected. The corrected radiosonde‐derived PW products (referred as Corr) were compared with the uncorrected products (referred as Raw) as well as PW products derived from the radiosonde data homogenized using the method proposed by Dai et al. (2011; referred as Dai, https://doi.org/10.1175/2010JCLI3816.1). Corr products show better agreements with GPS‐derived PW than Raw and Dai, and artificial significant decreasing PW trends in the recent two decades in Raw products were greatly reduced after applying the proposed corrections.

Variability and Trends in Global Precipitable Water Vapor Retrieved from COSMIC Radio Occultation and Radiosonde Observations

The spatial and temporal variations in global precipitable water (PW) derived from satellite and radiosonde observations during 2007–2016 are compared and analyzed in this study. The two observations show a good agreement in global spatiotemporal distributions and trends in PW. Generally, PW shows apparent latitudinal and seasonal variations. The averaged PW peaks in the tropical region, with the value of 40 mm or higher, and then decreases apparently to the polar region, less than 10 mm. PWs are larger in warm seasons and smaller in cold seasons for both hemispheres. It is indicated that the spatial and seasonal variabilities of PW are highly related to water vapor source and surface temperature as a direct heat source. The global PWs have changed in the past 60 years and, to some extent, strongly in the recent 10 years. It is found that PWs at Australian stations present statistically significant decreasing trends in last 60 years, while PWs at most stations in the United States have increasing trends. According to the global observations, it is found that PWs show uptrends over land and downtrends over the ocean in last 10 years, implying the widespread increase of water vapor in the troposphere over land.

Multiscale Variations of Precipitable Water over China Based on 1999–2015 Ground-Based GPS Observations and Evaluations of Reanalysis Products

Abstract The dense ground-based GPS provides a good tool to study water vapor distribution and multiscale variations, especially for linear trends on the interannual scale and short-term variations on the diurnal scale. It can also serve as an independent data source to evaluate performances of reanalyses. In this study, the 6-hourly precipitable water (PW) products at more than 260 GPS stations over China from 1999 to 2015 were analyzed and eight commonly used reanalyses, including 20CR version 2 (20CRv2), CFSR, ERA-Interim, JRA-25, JRA-55, MERRA, NCEP–NCAR, and NCEP–DOE AMIP-II, were evaluated. The climatological annual mean GPS PW distribution over China roughly shows a decreasing trend from southeast to northwest, with the largest annual and semiannual amplitudes in the lower reaches of the Yangtze River and mideastern China, respectively, and the smallest values in the Tibetan Plateau and southwestern China. All reanalyses (except for 20CRv2) can generally reproduce well the climatological annual mean PW (within 20%), annual amplitudes (within 20%), and semiannual amplitudes (within 20% except in the tropical monsoon region), but they all show wet biases in the Tibetan Plateau. Diurnal variation amplitudes reproduced by all reanalysis products are smaller than amplitudes estimated from GPS observations over China as a whole, and none of the reanalyses can capture the diurnal phases correctly. PW linear trends at most GPS stations in the recent 16 years are insignificant or with absolute values smaller than 0.10 mm yr−1. However, because of the assimilation of the unhomogenized radiosonde humidity data, most reanalyses show artificial decreasing PW trends (except in 20CRv2 and CFSR).

The Use of Ground-Based GPS Precipitable Water Measurements over China to Assess Radiosonde and ERA-Interim Moisture Trends and Errors from 1999 to 2015

Abstract Global positioning system (GPS) data from over 260 ground-based permanent stations in China covering the period from 1 March 1999 to 30 April 2015 were used to estimate precipitable water (PW) above each site with an accuracy of about 0.75 mm. Four types of radiosondes (referred to as GZZ2, GTS1, GTS1-1, and GTS1-2) were used in China during this period. Instrumentation type changes in radiosonde records were identified by comparing PW calculated from GPS and radiosonde data. Systematic errors in different radiosonde types introduced significant biases to the estimated PW trends at stations where more than one radiosonde type was used. Estimating PW trends from reanalysis products (ERA-Interim), which assimilate the unadjusted radiosonde humidity data, resulted in an artificial downward PW trend at almost all stations in China. The statistically significant GPS PW trends are predominantly positive, consistent in sign with the increase in moisture expected from the Clausius–Clapeyron relation due to a global temperature increase. The standard deviations of the differences between ERA-Interim and GPS PW in the summer were 3 times larger than the observational error of GPS PW, suggesting that potentially significant improvements to the reanalysis could be achieved by assimilating denser GPS PW observations over China. This work, based on an entirely independent GPS PW dataset, confirms previously reported significant differences in radiosonde PW trends when using corrected data. Furthermore, the dense geographical coverage of the all-weather GPS PW observations, especially in remote areas in western China, provides a valuable resource for calibrating regional trends in reanalysis products.

Global Water Vapor Trend from 1988 to 2011 and Its Diurnal Asymmetry Based on GPS, Radiosonde, and Microwave Satellite Measurements

Abstract This study analyzes trends in precipitable water (PW) over land and ocean from 1988 to 2011, the PW–surface temperature Ts relationship, and their diurnal asymmetry using homogenized radiosonde data, microwave satellite observations, and ground-based global positioning system (GPS) measurements. It is found that positive PW trends predominate over the globe, with larger magnitudes over ocean than over land. The PW trend is correlated with surface warming spatially over ocean with a pattern correlation coefficient of 0.51. The PW percentage increase rate normalized by Ts expressed as is larger and closer to the rate implied by the Clausius–Clapeyron (C–C) equation over ocean than over land. The 2-hourly GPS PW data show that the PW trend from 1995 to 2011 is larger at night than during daytime. Nighttime PW monthly anomalies correlate positively and significantly with nighttime minimum temperature Tmin at all stations, but this is not true for daytime PW and maximum temperature Tmax. The ratio of relative PW changes with Tmin () is larger and closer to the C–C equation’s implied value of ~7% K−1 than . This suggests that the relationship between PW and Ts at night is a better indicator of the water vapor feedback than that during daytime, when clouds and other factors also influence Ts.

Detecting Long-Term Trends in Precipitable Water over the Tibetan Plateau by Synthesis of Station and MODIS Observations*

Abstract Long-term trends in precipitable water (PW) are an important component of climate change assessments for the Tibetan Plateau (TP). PW products from Moderate Resolution Imaging Spectroradiometer (MODIS) are able to provide good spatial coverage of PW over the TP but limited in time coverage, while the meteorological stations in the TP can estimate long-term PW but unevenly distributed. To detect the decadal trend in PW over the TP, Bayesian inference theory is used to construct long-term and spatially continuous PW data for the TP based on the station and MODIS observations. The prior information on the monthly-mean PW from MODIS and the 63 stations over the TP for 2000–06 is used to get the posterior probability knowledge that is utilized to build a Bayesian estimation model. This model is then operated to estimate continuous monthly-mean PW for 1970–2011 and its performance is evaluated using the monthly MODIS PW anomalies (2007–11) and annual GPS PW anomalies (1995–2011), with RMSEs below 0.65 mm, to demonstrate that the model estimation can reproduce the PW variability over the TP in both space and time. Annual PW series show a significant increasing trend of 0.19 mm decade−1 for the TP during the 42 years. The most significant PW increase of 0.47 mm decade−1 occurs for 1986–99 and an insignificant decrease occurs for 2000–11. From the comparison of the PW data from JRA-55, ERA-40, ERA-Interim, MERRA, NCEP-2, and ISCCP, it is found that none of them are able to show the actual long-term trends and variability in PW for the TP as the Bayesian estimation.

A high-quality, homogenized, global, long-term (1993-2008) DORIS precipitable water data set for climate monitoring and model verification

For the first time a high-quality, consistent, global, long-term data set of zenith tropospheric delay (ZTD) and precipitable water (PW) is produced from Doppler orbitography radiopositioning integrated by satellite (DORIS) measurements at 81 sites. The data set was screened using a two-level procedure. First, postprocessing information is used to apply range checks and outlier checks to ZTD and formal error estimates. Second, outliers are detected by comparing DORIS ZTD with European Centre for Medium-Range Weather Forecasts reanalysis (ERA-Interim) data. These procedures reject 3% and 1% of the data, respectively. A linear drift is evidenced in the screened DORIS ZTD data compared to ERA-Interim and Global Positioning System (GPS) data, which potentially results from biases introduced by the progressive replacement of Alcatel antennas with Starec antennas. The DORIS PW is homogenized by applying a bias correction computed form comparison with ERA-Interim data each time station equipment is changed. The homogenized DORIS data are in excellent agreement with GPS data (correlation of 0.98 and standard deviation of differences of 1.5 kg m−2) and with ERA-Interim and satellite PW data (correlation > 0.95 and standard deviation of differences < 2.7 kg m−2). The agreement with radiosonde data is less good. Preliminary results of water vapor trends and variability are shown for 31 sites with more than 10 years of data. Good consistency is found between DORIS PW trends and ERA-Interim trends, which demonstrates the high potential of the DORIS PW data set for climate monitoring and model verification. The final DORIS PW data set is freely available in the supporting information.

Trends and variability in atmospheric precipitable water over the Tibetan Plateau for 2000-2010

The trends and variations in precipitable water (PW) over the Tibetan Plateau (TP) from 2000 to 2010 are analysed using the monthly mean PW datasets from Moderate Resolution Imaging Spectroradiometer (MODIS) and ERA-Interim reanalysis of European Centre for Medium-Range Weather Forecasts (ECMWF). Three different methods (including linear fit, non-parametric and non-linear) are used to estimate PW trends and their significance. The trend patterns derived from MODIS and ECMWF are very similar except for the magnitude. Increasing trends are found in the eastern and western TP; with decreasing trends in the middle. Atmospheric water vapour is more changeable compared to the surrounding areas and large PW anomalies occur frequently in July and August over the TP. Regression analysis between monthly mean anomalies of ECMWF PW and ECMWF surface air temperature (SAT) indicates reanalyses data show larger regression slope (7.36 +/- 0.75 % K-1) over the TP than the MODIS observations (4.81 +/- 0.72 % K-1) mainly in the non-monsoon season. The comparison of the vertically integrated moisture flux and its divergence between the wettest and driest monsoon seasons indicates that the PW spatial variability in monsoon seasons over the TP is affected by the large-scale atmospheric circulation. Although the TP region is under the influence of one large-scale circulation pattern (the monsoon) and the consistent warming background, the PW trends and the relation of PW and temperature are spatially heterogeneous, which is particularly important for predicting hydrological changes in this region.

Recent changes in tropospheric water vapor over the Arctic as assessed from radiosondes and atmospheric reanalyses

Changes in tropospheric water vapor over the Arctic are examined for the period 1979 to 2010 using humidity and temperature data from nine high latitude radiosonde stations north of 70°N with nearly complete records, and from six atmospheric reanalyses, emphasizing the three most modern efforts, MERRA, CFSR and ERA‐Interim. Based on comparisons with the radiosonde profiles, the reanalyses as a group have positive cold‐season humidity and temperature biases below the 850 hPa level and consequently do not capture observed low‐level humidity and temperature inversions. MERRA has the smallest biases. Trends in column‐integrated (surface to 500 hPa) water vapor (precipitable water) computed using data from the radiosondes and from the three modern reanalyses at the radiosonde locations are mostly positive, but magnitudes and statistical significance vary widely between sites and seasons. Positive trends in precipitable water from MERRA, CFSR and ERA‐Interim, largest in summer and early autumn, dominate the northern North Atlantic, including the Greenland, Norwegian and Barents seas, the Canadian Arctic Archipelago and (on the Pacific side) the Beaufort and Chukchi seas. This pattern is linked to positive anomalies in air and sea surface temperature and negative anomalies in end‐of‐summer sea ice extent. Trends from ERA‐Interim are weaker than those from either MERRA or CFSR. As assessed for polar cap averages (the region north of 70°N), MERRA, CFSR and ERA‐Interim all show increasing surface‐500 hPa precipitable over the analysis period encompassing most months, consistent with increases in 850 hPa air temperature and 850 hPa specific humidity. Data from all of the reanalyses point to strong interannual and decadal variability. The MERRA record in particular shows evidence of artifacts likely introduced by changes in assimilation data streams. A focus on the most recent decade (2001–2010) reveals large differences between the three reanalyses in the vertical structure of specific humidity and temperature anomalies.

Trends in Precipitable Water and Relative Humidity in China: 1979–2005

AbstractAnnual and seasonal trends of precipitable water (PW) and relative humidity (RH) at 850, 700, and 500 hPa are studied using the data from 106 radiosonde stations over China during the period 1979–2005. Analysis shows evidence of an increase in PW associated with the slight warming observed in the lower to midtroposphere over China. The northern part of China shows a significant upward trend of PW in summer, and drying of the atmosphere in winter is found in most regions over China. Annual and seasonal trends in RH at the 850-, 700-, and 500-hPa levels show no significant trends in most regions in China except for Xinjiang, which shows an upward trend, and central China, where there was a downward trend in RH at 500 hPa. It is found that changes in PW are coincident with the warming of the surface and the lower to midtroposphere. The RH in the lower to midtroposphere in most regions over China has remained steady during the most recent 30 years, as might be expected given the increasing of PW and the warming above the surface. The long-term trend of precipitation over China may be linked to the trends of PW and RH at the lower level and midlevel.

Radiosonde‐based trends in precipitable water over the Northern Hemisphere: An update

In an effort to update previous analyses of long‐term changes in column‐integrated water vapor, we have analyzed trends in surface‐to‐500‐hPa precipitable water (PW) calculated from radiosonde measurements of dew point depression, temperature, and pressure at approximately 300 stations in the Northern Hemisphere for the period 1973–2006. Inhomogeneities were addressed by applying a homogenization algorithm that adjusts for both documented and undocumented change points. The trends of the adjusted PW time series are predominantly upward, with a statistically significant trend of 0.45 mm decade−1 for the Northern Hemisphere land areas included in the analysis. Particularly significant increases are found in all seasons over the islands of the western tropical Pacific, and trends are also positive and statistically significant for the year as a whole and in at least one season in Japan and the United States. These results indicate that the widespread increases in tropospheric water vapor, which earlier studies had reported and shown to be physically consistent with concurrent increases in temperature and changes in moisture transport, have continued in recent years.

The Interannual Variability and Trend of Precipitable Water over Southern Greece

AbstractThe precipitable water (PW) content was estimated over southern Greece for three atmospheric layers, using 28-yr twice-daily radiosonde measurements of temperature, humidity, and atmospheric pressure. Precipitable water demonstrates considerable variation at the monthly and interannual time scales as well as statistically significant upward trends at the annual level and for June–August (JJA) and September–November (SON). The relationship between PW and surface climate was also found to vary by season and surface climate variable. Disaggregation of seasonal PW trends by synoptic type revealed that seasonal trends might be attributed to increases in moisture in a limited number of airmass types such that maritime air masses appear to be becoming moister while their continental counterparts are drying. Despite fundamental changes to the intrinsic PW properties of air masses for some synoptic categories, the significance of these for determining the overall trend in seasonal PW levels is related to their weighted contribution as determined by changing airmass frequency. Consequently, the climatological effects of a moistening or drying air mass may be offset by a declining frequency. It is also shown that increasing PW trends cannot be attributed unequivocally to airmass warming as significant increases in PW have occurred in conjunction with falling temperatures in some seasons and airmass types. Accordingly, factors other than the commonly assumed global-warming-related increase in atmospheric moisture via the link between temperature and saturation vapor pressure must be considered if the mechanisms responsible for PW trends over southern Greece are to be fully understood.

Trends and variability in column-integrated atmospheric water vapor

An analysis and evaluation has been performed of global datasets on column-integrated water vapor (precipitable water). For years before 1996, the Ross and Elliott radiosonde dataset is used for validation of European Centre for Medium-range Weather Forecasts (ECMWF) reanalyses ERA-40. Only the special sensor microwave imager (SSM/I) dataset from remote sensing systems (RSS) has credible means, variability and trends for the oceans, but it is available only for the post-1988 period. Major problems are found in the means, variability and trends from 1988 to 2001 for both reanalyses from National Centers for Environmental Prediction (NCEP) and the ERA-40 reanalysis over the oceans, and for the NASA water vapor project (NVAP) dataset more generally. NCEP and ERA-40 values are reasonable over land where constrained by radiosondes. Accordingly, users of these data should take great care in accepting results as real. The problems highlight the need for reprocessing of data, as has been done by RSS, and reanalyses that adequately take account of the changing observing system. Precipitable water variability for 1988–2001 is dominated by the evolution of ENSO and especially the structures that occurred during and following the 1997–98 El Nino event. The evidence from SSM/I for the global ocean suggests that recent trends in precipitable water are generally positive and, for 1988 through 2003, average 0.40±0.09 mm per decade or 1.3±0.3% per decade for the ocean as a whole, where the error bars are 95% confidence intervals. Over the oceans, the precipitable water variability relates very strongly to changes in SSTs, both in terms of spatial structure of trends and temporal variability (with a regression coefficient for 30°N–30°S of 7.8% K−1) and is consistent with the assumption of fairly constant relative humidity. In the tropics, the trends are also influenced by changes in rainfall which, in turn, are closely associated with the mean flow and convergence of moisture by the trade winds. The main region where positive trends are not very evident is over Europe, in spite of large and positive trends over the North Atlantic since 1988. A much longer time series is probably required to obtain stable patterns of trends over the oceans, although the main variability could probably be deduced from past SST and associated precipitation variations.

Atmospheric Water Vapor over China

Abstract Chinese radiosonde data from 1970 to 1990 are relatively homogeneous in time and are used to examine the climatology, trends, and variability of China’s atmospheric water vapor content. The climatological distribution of precipitable water (PW) is primarily dependent on surface temperature. Influenced by the east Asia monsoon, China’s precipitable water exhibits very large seasonal variations. Station elevation is also a dominant factor affecting water vapor distribution in China. An increase (decrease) in precipitable water over China is associated with an increase (decrease) of precipitation in most regions. Increases in the percentage of PW relative to climatology are greater in winter and spring than in summer and autumn. Interannual variation and trends in precipitable water and surface temperature are closely correlated in China, confirming a positive “greenhouse” feedback. Interannual variations between precipitable water and precipitation are also significantly correlated.