Many of the major advances in the field have occurred within the last decade, which is part of the motivation for the present review. General circulation models with isotope-enabled microphysics schemes first became available in the 1980s, with more widespread use beginning in the 1990s. This was followed by the advent of laser absorption spectroscopic techniques in the 1990s. The earliest studies of water vapor isotopic composition relied on cryogenic and mass spectrometric techniques, which dominated the field until the mid-1990s, when the first space-based measurements were obtained with the Atmospheric Trace Molecule Spectroscopy (ATMOS) instrument which flew aboard the space shuttle in 1994. Comparisons between observations and numerical models of water vapor isotopic composition can lead to improved interpretations of the governing hydrological processes, and can also help diagnose deficiencies within the models themselves. These studies can also inform paleoclimate interpretations from proxy records by improving our understanding of the whole suite of atmospheric processes that govern the isotopic composition of precipitation that is recorded in such proxies. Studies of atmospheric water vapor isotopic composition can provide first-order constraints on the modern atmospheric hydrological cycle by constraining the relative roles of phase changes, transport, and mixing in ways that are difficult with measurements of water vapor mixing ratio alone. In the last several years, there has been a tremendous expansion in the number of datasets of water vapor isotopic composition and a substantially improved set of theories and models for interpreting them. The paleoclimate archives in glacial ice and in speleothems are also influenced by these processes, which are discussed in detail in Section 6. Blue arrows indicate processes that tend to isotopically deplete water vapor and red arrows indicate processes that tend to isotopically enrich water vapor. Finally, studies of the processes governing modern water vapor isotopic composition provide an improved framework for the interpretation of paleoclimate proxy records of the hydrological cycle.Ĭartoon illustrating key processes governing the isotopic composition of atmospheric water vapor. The combination of improved measurement and modeling of water vapor isotopic composition opens the door to new advances in our understanding of the atmospheric water cycle, in processes ranging from the marine boundary layer, through deep convection and tropospheric mixing, and into the water cycle of the stratosphere. The incorporation of isotopes into GCMs has enabled more detailed diagnostics of the water cycle and has led to improvements in its simulation. The simulation of water vapor isotopic composition has evolved from General Circulation Model (GCM) methods for simulating precipitation isotopic composition to sophisticated isotope-enabled microphysics schemes using higher-order moments for water- and ice-size distributions. The technologies for in-situ and remote sensing measurements of water vapor isotopic composition have developed especially rapidly over the last decade, with discrete water vapor sampling methods, based on mass spectroscopy, giving way to laser spectroscopic methods and satellite- and ground-based infrared absorption techniques. Theories for water vapor isotopic composition have been developed by extending the theories that have been used for the isotopic composition of precipitation to include a more nuanced understanding of evaporation, large-scale mixing, deep convection, and kinetic fractionation.

The measurement and simulation of water vapor isotopic composition has matured rapidly over the last decade, with long-term datasets and comprehensive modeling capabilities now available.

Randa haak chamberlain sd