Jeonghoon Lee

Bio: Jeonghoon Lee is an academic researcher from Ewha Womans University. The author has contributed to research in topics: Snow & Meltwater. The author has an hindex of 16, co-authored 63 publications receiving 1129 citations. Previous affiliations of Jeonghoon Lee include Seoul National University & Dartmouth College.

Process-evaluation of tropospheric humidity simulated by general circulation models using water vapor isotopologues: 1. Comparison between models and observations

Abstract: The goal of this study is to determine how H2O and HDO measurements in water vapor can be used to detect and diagnose biases in the representation of processes controlling tropospheric humidity in atmospheric general circulation models (GCMs). We analyze a large number of isotopic data sets (four satellite, sixteen ground-based remote-sensing, five surface in situ and three aircraft data sets) that are sensitive to different altitudes throughout the free troposphere. Despite significant differences between data sets, we identify some observed HDO/H2O characteristics that are robust across data sets and that can be used to evaluate models. We evaluate the isotopic GCM LMDZ, accounting for the effects of spatiotemporal sampling and instrument sensitivity. We find that LMDZ reproduces the spatial patterns in the lower and mid troposphere remarkably well. However, it underestimates the amplitude of seasonal variations in isotopic composition at all levels in the subtropics and in midlatitudes, and this bias is consistent across all data sets. LMDZ also underestimates the observed meridional isotopic gradient and the contrast between dry and convective tropical regions compared to satellite data sets. Comparison with six other isotope-enabled GCMs from the SWING2 project shows that biases exhibited by LMDZ are common to all models. The SWING2 GCMs show a very large spread in isotopic behavior that is not obviously related to that of humidity, suggesting water vapor isotopic measurements could be used to expose model shortcomings. In a companion paper, the isotopic differences between models are interpreted in terms of biases in the representation of processes controlling humidity. Copyright © 2012 by the American Geophysical Union.

Process-evaluation of tropospheric humidity simulated by general circulation models using water vapor isotopic observations: 2. Using isotopic diagnostics to understand the mid and upper tropospheric moist bias in the tropics and subtropics

Abstract: Evaluating the representation of processes controlling tropical and subtropical tropospheric relative humidity (RH) in atmospheric general circulation models (GCMs) is crucial to assess the credibility of predicted climate changes. GCMs have long exhibited a moist bias in the tropical and subtropical mid and upper troposphere, which could be due to the mis-representation of cloud processes or of the large-scale circulation, or to excessive diffusion during water vapor transport. The goal of this study is to use observations of the water vapor isotopic ratio to understand the cause of this bias. We compare the three-dimensional distribution of the water vapor isotopic ratio measured from space and ground to that simulated by several versions of the isotopic GCM LMDZ. We show that the combined evaluation of RH and of the water vapor isotopic composition makes it possible to discriminate the most likely cause of RH biases. Models characterized either by an excessive vertical diffusion, an excessive convective detrainment or an underestimated in situ cloud condensation will all produce a moist bias in the free troposphere. However, only an excessive vertical diffusion can lead to a reversed seasonality of the free tropospheric isotopic composition in the subtropics compared to observations. Comparing seven isotopic GCMs suggests that the moist bias found in many GCMs in the mid and upper troposphere most frequently results from an excessive diffusion during vertical water vapor transport. This study demonstrates the added value of water vapor isotopic measurements for interpreting shortcomings in the simulation of RH by climate models. Copyright 2012 by the American Geophysical Union.

Isotopic evolution of a seasonal snowcover and its melt by isotopic exchange between liquid water and ice

Abstract: Abstract Understanding an isotopic evolution of a snowpack is important for both climate and hydrological studies, because the snowmelt is a significant component of groundwater and surface runoff in temperate areas. In this work, we studied oxygen and hydrogen isotopic evolution from new snow to snow profile and to meltwater through two winter seasons (1998 and 2001) at the Central Sierra Snow Laboratory, California, USA. The slopes of the δD vs. δ18O regression for the new snow are similar to that of the global meteoric water line (GMWL) of 8. However, this slope decreases in the snow profile and decreases further in the meltwater. We attribute this systematic slope changes to the isotopic exchange between ice and liquid water that is generated at the snow surface by melting and flows through the snowpack by percolation. A physically-based one-dimensional model, including melting of snow at the surface and isotopic exchange between percolating water and ice, was used to simulate isotopic variation of snowmelt in 2001. A successful simulation was obtained for the δD–δ18O slope of snowmelt (6.5), which is significantly lower than the slope of the meteoric water line (8.2) defined by the new snow. This result indicates that the liquid water evaporation should not be considered as the only process that yields slopes of the δD vs. δ18O relationship in surface water and groundwater. The d-excess of the snowmelt is changed from the original snow because of the δD–δ18O relationship controlled by ice–liquid exchange. With a δD–δ18O slope less than 8, the d-excess would be anti-correlated with δD or δ18O. The model is also used to examine how isotopic heterogeneity of a snowpack affects the isotopic redistribution in the pore water, ice and meltwater of the snowpack. The results show that isotopic heterogeneity of the snowpack may significantly affect the temporal changes in the δD–δ18O slopes, and a measured slope at a given time is a combined result of meteorological conditions, which affect both isotopic composition of the original snow and the process of snow metamorphism, and the melting history of the snowpack.

Comparison of an isotopic atmospheric general circulation model with new quasi-global satellite measurements of water vapor isotopologues

Abstract: We performed an intensive comparison of an isotope-incorporated atmospheric general circulation model with vapor isotopologue ratio observation data by two quasi-global satellite sensors in preparation for data assimilation of water isotope ratios. A global Isotope-incorporated Global Spectral Model simulation nudged toward the reanalysis wind field, atmospheric total column data from Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) on Envisat, and midtropospheric (800 to 500 hPa) data from Tropospheric Emission Spectrometer (TES) on Aura were used. For the mean climatological δD of both the total atmospheric column and the midtroposphere layer, the model reproduced their geographical variabilities quite well. There is, however, some degree of underestimation of the latitudinal gradient (higher δD in the tropics and lower δD in midlatitudes) compared to the SCIAMACHY data, whereas there is generally less disagreement except lower δD over the Maritime Continent compared to the TES data. It was also found that the two satellite products have different relationships between water vapor amount and isotopic composition. Particularly, atmospheric column mean δD, which is dominated by lower-tropospheric vapor, closely follows the fractionation pattern of a typical Rayleigh-type “rain out” process, whereas in the midtroposphere the relationship between isotopic composition and vapor amount is affected by a “mixing” process. This feature is not reproduced by the model, where the relationships between δD and the vapor are similar to each other for the atmospheric column and midtroposphere. Comparing on a shorter time scale, it becomes clear that the data situation for future data assimilation for total column δD is most favorable for tropical and subtropical desert areas (i.e., Sahel, southern Africa, mideastern Asia, Gobi, Australia, and the southwest United States), whereas the available midtropospheric δD observations cover wider regions, particularly over tropical to subtropical oceans.

A review of climatic controls on δ18O in precipitation over the Tibetan Plateau: Observations and simulations

Abstract: The stable oxygen isotope ratio (δ18O) in precipitation is an integrated tracer of atmospheric processes worldwide. Since the 1990s, an intensive effort has been dedicated to studying precipitation isotopic composition at more than 20 stations in the Tibetan Plateau (TP) located at the convergence of air masses between the westerlies and Indian monsoon. In this paper, we establish a database of precipitation δ18O and use different models to evaluate the climatic controls of precipitation δ18O over the TP. The spatial and temporal patterns of precipitation δ18O and their relationships with temperature and precipitation reveal three distinct domains, respectively associated with the influence of the westerlies (northern TP), Indian monsoon (southern TP), and transition in between. Precipitation δ18O in the monsoon domain experiences an abrupt decrease in May and most depletion in August, attributable to the shifting moisture origin between Bay of Bengal (BOB) and southern Indian Ocean. High-resolution atmospheric models capture the spatial and temporal patterns of precipitation δ18O and their relationships with moisture transport from the westerlies and Indian monsoon. Only in the westerlies domain are atmospheric models able to represent the relationships between climate and precipitation δ18O. More significant temperature effect exists when either the westerlies or Indian monsoon is the sole dominant atmospheric process. The observed and simulated altitude-δ18O relationships strongly depend on the season and the domain (Indian monsoon or westerlies). Our results have crucial implications for the interpretation of paleoclimate records and for the application of atmospheric simulations to quantifying paleoclimate and paleo-elevation changes.

Oceanic and terrestrial sources of continental precipitation

Abstract: [1] The most important sources of atmospheric moisture at the global scale are herein identified, both oceanic and terrestrial, and a characterization is made of how continental regions are influenced by water from different moisture source regions. The methods used to establish source-sink relationships of atmospheric water vapor are reviewed, and the advantages and caveats associated with each technique are discussed. The methods described include analytical and box models, numerical water vapor tracers, and physical water vapor tracers (isotopes). In particular, consideration is given to the wide range of recently developed Lagrangian techniques suitable both for evaluating the origin of water that falls during extreme precipitation events and for establishing climatologies of moisture source-sink relationships. As far as oceanic sources are concerned, the important role of the subtropical northern Atlantic Ocean provides moisture for precipitation to the largest continental area, extending from Mexico to parts of Eurasia, and even to the South American continent during the Northern Hemisphere winter. In contrast, the influence of the southern Indian Ocean and North Pacific Ocean sources extends only over smaller continental areas. The South Pacific and the Indian Ocean represent the principal source of moisture for both Australia and Indonesia. Some landmasses only receive moisture from the evaporation that occurs in the same hemisphere (e.g., northern Europe and eastern North America), while others receive moisture from both hemispheres with large seasonal variations (e.g., northern South America). The monsoonal regimes in India, tropical Africa, and North America are provided with moisture from a large number of regions, highlighting the complexities of the global patterns of precipitation. Some very important contributions are also seen from relatively small areas of ocean, such as the Mediterranean Basin (important for Europe and North Africa) and the Red Sea, which provides water for a large area between the Gulf of Guinea and Indochina (summer) and between the African Great Lakes and Asia (winter). The geographical regions of Eurasia, North and South America, and Africa, and also the internationally important basins of the Mississippi, Amazon, Congo, and Yangtze Rivers, are also considered, as is the importance of terrestrial sources in monsoonal regimes. The role of atmospheric rivers, and particularly their relationship with extreme events, is discussed. Droughts can be caused by the reduced supply of water vapor from oceanic moisture source regions. Some of the implications of climate change for the hydrological cycle are also reviewed, including changes in water vapor concentrations, precipitation, soil moisture, and aridity. It is important to achieve a combined diagnosis of moisture sources using all available information, including stable water isotope measurements. A summary is given of the major research questions that remain unanswered, including (1) the lack of a full understanding of how moisture sources influence precipitation isotopes; (2) the stationarity of moisture sources over long periods; (3) the way in which possible changes in intensity (where evaporation exceeds precipitation to a greater of lesser degree), and the locations of the sources, (could) affect the distribution of continental precipitation in a changing climate; and (4) the role played by the main modes of climate variability, such as the North Atlantic Oscillation or the El Nino–Southern Oscillation, in the variability of the moisture source regions, as well as a full evaluation of the moisture transported by low-level jets and atmospheric rivers.

Illuminating hydrological processes at the soil-vegetation-atmosphere interface with water stable isotopes

Abstract: Funded by DFG research project “From Catchments as Organised Systems to Models based on Functional Units” (FOR 1

Aerosol indirect effects -- general circulation model intercomparison and evaluation with satellite data

Abstract: Aerosol indirect effects continue to constitute one of the most important uncertainties for anthropogenic climate perturbations. Within the international AEROCOM initiative, the representation of aerosol-cloud-radiation interactions in ten different general circulation models (GCMs) is evaluated using three satellite datasets. The focus is on stratiform liquid water clouds since most GCMs do not include ice nucleation effects, and none of the model explicitly parameterizes aerosol effects on convective clouds. We compute statistical relationships between aerosol optical depth (Ta) and various cloud and radiation quantities in a manner that is consistent between the models and the satellite data. It is found that the model-simulated influence of aerosols on cloud droplet number concentration (Nd) compares relatively well to the satellite data at least over the ocean. The relationship between Ta and liquid water path is simulated much too strongly by the models. It is shown that this is partly related to the representation of the second aerosol indirect effect in terms of autoconversion. A positive relationship between total cloud fraction (fcld) and Ta as found in the satellite data is simulated by the majority of the models, albeit less strongly than that in the satellite data in most of them. In a discussion of the hypotheses proposed in the literature to explain the satellite-derived strong fcld - Ta relationship, our results indicate that none can be identified as unique explanation. Relationships similar to the ones found in satellite data between Ta and cloud top temperature or outgoing long-wave radiation (OLR) are simulated by only a few GCMs. The GCMs that simulate a negative OLR - Ta relationship show a strong positive correlation between Ta and fcld The short-wave total aerosol radiative forcing as simulated by the GCMs is strongly influenced by the simulated anthropogenic fraction of Ta, and parameterisation assumptions such as a lower bound on Nd. Nevertheless, the strengths of the statistical relationships are good predictors for the aerosol forcings in the models. An estimate of the total short-wave aerosol forcing inferred from the combination of these predictors for the modelled forcings with the satellite-derived statistical relationships yields a global annual mean value of -1.5+-0.5 Wm-2. An alternative estimate obtained by scaling the simulated clear- and cloudy-sky forcings with estimates of anthropogenic Ta and satellite-retrieved Nd - Ta regression slopes, respectively, yields a global annual mean clear-sky (aerosol direct effect) estimate of -0.4+-0.2 Wm-2 and a cloudy-sky (aerosol indirect effect) estimate of -0.7+-0.5 Wm-2, with a total estimate of -1.2+-0.4 Wm-2.