Global Precipitable Water Research Articles

Significant Increase in African Water Vapor over 2001–2020

Atmospheric water vapor is not only a key element of the global hydrological cycle but also the most abundant greenhouse gas. The phase transition and transportation of water vapor are essential for maintaining global energy balance and regulating hydrological processes. However, due to insufficient meteorological observational data, climate research in Africa faces significant limitations despite its substantial contribution to changes in global precipitable water vapor (PWV). In this study, we used MODIS near-infrared (NIR) PWV products and Berkeley temperature data to depict the spatial–temporal variability in PWV across Africa from 2001 to 2020. The results reveal a significant increasing trend in PWV over Africa, with an increase of 0.0158 cm/year. Nearly 99.96% of Africa shows an increase in PWV, with 88.95% of these areas experiencing statistically significant changes, particularly in central regions of Africa. The increase in PWV is more pronounced in high-value months compared to low-value months. The equatorial region of the Congo Basin exhibits higher PWV, which gradually decreases as latitude increases. Despite significant warming (0.0162 °C/year) in Africa, there is no consistent positive correlation between temperature and water vapor. A positive relationship between PWV and temperature is observed in western Africa, while a negative relationship is noted in eastern and southern Africa on an annual scale. Additionally, an increasing trend in precipitation (4.6669 mm/year) is observed, with a significant positive correlation between PWV and precipitation across most of Africa, although this relationship varies by month. These findings provide valuable insights into the comprehension of the hydrothermal variation in Africa amidst climate warming.

Rising trends of global precipitable water vapor and its correlation with flood frequency

Using 4 global reanalysis data sets, significant upward trends of precipitable water vapor (PWV) were found in the 3 time periods of 1958–2020, 1979–2020, and 2000–2020. During 1958–2020, the global PWV trends obtained using the ERA5 and JRA55 data sets are 0.19 ± 0.01 mm per decade (1.15 ± 0.31%) and 0.23 ± 0.01 mm per decade (1.45 ± 0.32%), respectively. The PWV trends obtained using the ERA5, JRA55, NCEP-NCAR, and NCEP-DOE data sets are 0.22 ± 0.01 mm per decade (1.18 ± 0.54%), 0.21 ± 0.00 mm per decade (1.76 ± 0.56%), 0.27 ± 0.01 mm per decade (2.20 ± 0.70%) and 0.28 ± 0.01 mm per decade (2.19 ± 0.70%) for the period 1979–2020. During 2000–2020, the PWV trends obtained using ERA5, JRA55, NCEP-DOE, and NCEP-NCAR data sets are 0.40 ± 0.25 mm per decade (2.66 ± 1.51%), 0.37 ± 0.24 mm per decade (2.19 ± 1.54%), 0.40 ± 0.26 mm per decade (1.96 ± 1.53%) and 0.36 ± 0.25 mm per decade (2.47 ± 1.72%), respectively. Rising PWV has a positive impact on changes in precipitation, increasing the probability of extreme precipitation and then changing the frequency of flood disasters. Therefore, exploring the relationship between PWV (derived from ERA5 and JRA55) change and flood disaster frequency from 1958 to 2020 revealed a significant positive correlation between them, with correlation coefficients of 0.68 and 0.79, respectively, which explains the effect of climate change on the increase in flood disaster frequency to a certain extent. The study can provide a reference for assessing the evolution of flood disasters and predicting their frequency trends.

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.

Low Dimensional Embedding of Climate Data for Radio Astronomical Site Testing in the Colombian Andes

We set out to evaluate the potential of the Colombian Andes for millimeter-wave astronomical observations. Previous studies for astronomical site testing in this region have suggested that nighttime humidity and cloud cover conditions make most sites unsuitable for professional visible-light observations. Millimeter observations can be done during the day, but require that the precipitable water vapor column above a site stays below ∼10 mm. Due to a lack of direct radiometric or radiosonde measurements, we present a method for correlating climate data from weather stations to sites with a low precipitable water vapor column. We use unsupervised learning techniques to low dimensionally embed climate data (precipitation, rain days, relative humidity, and sunshine duration) in order to group together stations with similar long-term climate behavior. The data were taken over a period of 30 years by 2046 weather stations across the Colombian territory. We find six regions with unusually dry, clear-sky conditions, ranging in elevations from 2200 to 3800 masl. We evaluate the suitability of each region using a quality index derived from a Bayesian probabilistic analysis of the station type and elevation distributions. Two of these regions show a high probability of having an exceptionally low precipitable water vapor column. We compared our results with global precipitable water vapor maps and find a plausible geographical correlation with regions with low water vapor columns (∼10 mm) at an accuracy of ∼20 km. Our methods can be applied to similar data sets taken in other countries as a first step toward astronomical site evaluation.

Global water vapor variability and trend from the latest 36 year (1979 to 2014) data of ECMWF and NCEP reanalyses, radiosonde, GPS, and microwave satellite

AbstractThe variability and trend in global precipitable water vapor (PWV) from 1979 to 2014 are analyzed using the PWV data sets from the ERA‐Interim reanalysis of the European Centre for Medium‐Range Weather Forecasts (ECMWF), reanalysis of the National Centers for Environmental Prediction (NCEP), radiosonde, Global Positioning System (GPS), and microwave satellite observations. PWV data from the ECMWF and NCEP have been evaluated by radiosonde, GPS, and microwave satellite observations, showing that ECMWF has higher accuracy than NCEP. Over the oceans, ECMWF has a much better agreement with the microwave satellite than NCEP. An upward trend in the global PWV is evident in all the five PWV data sets over three study periods: 1979–2014, 1992–2014, and 2000–2014. Positive global PWV trends, defined as percentage normalized by annual average, of 0.61 ± 0.33% decade−1, 0.57 ± 0.28% decade−1, and 0.17 ± 0.35% decade−1, have been derived from the NCEP, radiosonde, and ECMWF, respectively, for the period 1979–2014. It is found that ECMWF overestimates the PWV over the ocean prior to 1992. Thus, two more periods, 1992–2014 and 2000–2014, are studied. Increasing PWV trends are observed from all the five data sets in the two periods: 1992–2014 and 2000–2014. The linear relationship between PWV and surface temperature is positive over most oceans and the polar region. Steep positive/negative regression slopes are generally found in regions where large regional moisture flux divergence/convergence occurs.

Characteristics of global precipitable water in ENSO events revealed by COSMIC measurements

Precipitable water (PW) retrievals from FORMOSAT‐3/Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) Global Positioning System (GPS) radio occultation (RO) measurements were analyzed and compared with those derived from Special Sensor Microwave/Imager (SSM/I) and Advanced Microwave Scanning Radiometer for Earth Observation System (AMSR‐E) during the El Niño‐Southern Oscillation (ENSO) events from 2007 to 2011. For the three ENSO events in 2007–2011, monthly mean binned COSMIC PW results are in a very high correlation (up to 0.98) with those of SSM/I and AMSR‐E over the ocean, generally with root‐mean‐square differences less than 4 mm. PW retrievals from the three satellites are also of similar latitudinal variations. However, the PW is slightly underestimated by GPS RO, in particular, in the tropical regions. This underestimate may be caused partially by the fact that not all RO measurements can reach the surface. Inter‐satellite PW anomaly comparisons for the winter months in the ENSO events, with respect to those during the neutral (non‐ENSO) months, show consistent ENSO signals with major PW anomaly near the central Pacific in the warm event and near the Indonesian region and east of Australia in the two cold events. However, the 2007/2008 La Niña is somewhat less correlated for COSMIC with AMSR‐E and SSM/I. For the stronger 2010/2011 La Niña, their PW anomalies are in higher correlations of about 0.8.

NVAP and Reanalysis-2 Global Precipitable Water Products : Intercomparison and Variability Studies

In this study similarities and differences between NASA's Water Vapor Project (NVAP) and NCEP–NCAR's reanalysis-2 total precipitable water (TPW) datasets are investigated, along with an assessment of its space–time variability, using simple statistical techniques. Global and hemispheric, as well as annual and seasonal differences between the two datasets are analyzed in detail. It is found that, in general, both datasets show very similar spatial and temporal patterns of variability, and there is a good correlation between them. The spatial TPW variability is closely related to latitudinal and altitudinal variations, and temporal TPW variability is strongly related to monsoon and ENSO events. In spite of the similarity in the patterns, there are significant differences in the magnitudes of TPW amount and variability between the two datasets. At the global scale it is found that the NCEP–NCAR reanalyis-2 product shows a more moist atmosphere than NVAP. On the other hand, variability analyses show that NVAP...

Climatology and interannual variability of diurnal water vapor heating

Tropospheric heating by water vapor absorption of near‐infrared (IR) radiation is a leading drive of the propagating diurnal tide. A climatology of monthly diurnal water vapor IR heating rates is derived using National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis and a global precipitable water (PW) data set. The new climatology updates an existing one compiled in 1982 that provides seasonally averaged IR heating between 35°S and 35°N. The new heating rates have greater temporal and spatial resolution and enable examination of intraseasonal and year‐to‐year variability over the 10‐year span of the PW data set. Our findings suggest that tropical tropospheric variability may be communicated to the diurnal tide (and possibly the middle and upper atmosphere) by means of water vapor heating.

Variability of the global precipitable water with a timescale of 90–150 days

A 90–150 day signal is identified in the global precipitable water field generated by the Global Data Assimilation Systems (GDAS) of the Goddard Laboratory for Atmospheres (GLA), National Meteorological Center, and European Centre for Medium‐Range Weather Forecasts. The finding of this intraseasonal signal in global precipitable water is significant for two reasons: (1) it suggests that there is 90–150 day intraseasonal variability in the atmospheric branch of the global hydrological cycle and (2) it provides a useful parameter to test the sensitivity of the GDAS‐generated hydrological data. This newly identified intraseasonal signal in the global precipitable water was verified with Special Sensor Microwave/Imager precipitable water data over oceans and station‐mixing ratio data over the continental United States. Based upon some simple statistical analyses and global and regional composite charts, it was found that the 90–150 day low‐frequency oscillations contained in different GDAS data sets are more coherent with each other in regions with good data coverage but are poorly correlated over the data‐sparse areas. Furthermore, the GLA GDAS provides the most realistic representation of this intraseasonal global precipitable water signal.

Annual variation of the global precipitable water and its maintenance: observation and climate-simulation

Annual variation of the global precipitable water and its maintenance: observation and climate-simulation

Annual variation of the global precipitable water and its maintenance: observation and climate-simulation

The annual variation of the global-mean precipitable water 〈W〉and the associated hydrological cycle were analyzed with the upper-air data generated by the Global Data Assimilation System of the National Meteorological Center for 1981–1991 and the European Centre for Medium Range Weather Forecasts from 1983–1991. It was found that the annual variation of 〈W〉 coincides with that of the Northern Hemisphere precipitable water [W]NH. The hemispheric-mean ([ ]) water budget analysis shows that water vapor is transported from the winter to the summer hemisphere across the equator by the Hadley circulation, and that the annual variations in the water vapor sink [P – E] for both hemispheres also follow the same seasonal march. The amplitudes of the annual variations in these two hydrological processes are comparable in both hemispheres. Thus, the annual variations of [W]NH and [W]SH are the result of slight imbalances between the cross-equator water vapor transport and the water vapor sink, particularly in the spring and fall. The climatological hemispheric-mean water budgets reveal that the Southern Hemisphere is a water vapor source and the Northern Hemisphere is a water vapor sink. The cross-equator water vapor transport constitutes a major source acting to maintain [W]NH, and in turn 〈W〉. The hydrological mechanism maintaining the observed 〈W〉 annual variation is consistent with that obtained from the hydrological cycle in a 10-year (1979–1988) climate simulation done at the Goddard Laboratory for Atmospheres as part of their participation in the Atmospheric Model Intercomparison Project (AMIP). DOI: 10.1034/j.1600-0870.1996.00001.x

Global Water Vapor Flux and Maintenance during FGGE

Abstract The relative humidity, temperature and wind fields generated by the First Global GARP Experiment (FGGE) III-b analysis of the Geophysical Fluid Dynamics Laboratory (GFDL) are used to examine the global precipitable water distribution, and the water vapor transport and maintenance for two extreme seasons of atmospheric circulation, i.e., December–February and June–August 1979. It has been observed that the major water vapor content exists in tropical areas, especially over three regions: equatorial Africa, the northern part of South America, and equatorial western Pacific in December-February; equatorial Africa, Central America and the northern part of South America, and monsoon areas in June-August. The water vapor transport was analyzed to explore how the high water vapor content of these areas is maintained by the large-scale atmospheric circulation. It is concluded that 1) the nondivergent stationary mode describes most of the atmospheric water vapor transport; 2) the stationary divergent mode...