Benjamin R. Lintner

Asian monsoon hydrometeorology from TES and SCIAMACHY water vapor isotope measurements and LMDZ simulations: Implications for speleothem climate record interpretation

Observations show that heavy oxygen isotope composition in precipitation (δ^(18)O_p) increases from coastal southeastern (SE) China to interior northwestern (NW) China during the wet season, contradicting expectations from simple Rayleigh distillation theory. Here we employ stable isotopes of precipitation and vapor from satellite measurements and climate model simulations to characterize the moisture processes that control Asian monsoon precipitation and relate these processes to speleothem paleoclimate records. We find that δ^(18)O_p is low over SE China as a result of local and upstream condensation and that δ^(18)O_p is high over NW China because of evaporative enrichment of ^(18)O as raindrops fall through dry air. We show that δ^(18)O_p at cave sites over southern China is weakly correlated with upstream precipitation in the core of the Indian monsoon region rather than local precipitation, but it is well-correlated with the δ^(18)O_p over large areas of southern and central China, consistent with coherent speleothem δ^(18)O_p variations over different parts of China. Previous studies have documented high correlations between speleothem δ^(18)O_p and millennial timescale climate forcings, and we suggest that the high correlation between insolation and speleothem δ^(18)O_p in southern China reflects the variations of hydrologic processes over the Indian monsoon region on millennial and orbital timescales. The δ^(18)O_p in the drier part (north of ∼30°N) of China, on the other hand, has consistently negative correlations with local precipitation and may capture local hydrologic processes related to changes in the extent of the Hadley circulation.

Mechanisms of Remote Tropical Surface Warming during El Niño

Abstract The authors demonstrate through atmospheric general circulation model (the Community Climate Model version 3.10) simulations of the 1997/98 El Nino that the observed “remote” (i.e., outside the Pacific) tropical land and ocean surface warming appearing a few months after the peak of the El Nino event is causally linked to the Tropics-wide warming of the troposphere resulting from increased atmospheric heating in the Pacific, with the latter acting as a conduit for the former. Unlike surface temperature, the surface flux behavior in the remote Tropics in response to El Nino is complex, with sizable spatial variation and compensation between individual flux components; this complexity suggests a more fundamental control (i.e., tropospheric temperature) for the remote tropical surface warming. Over the remote oceans, latent heat flux acting through boundary layer humidity variations is the important regulator linking the surface warming in the model simulations to the tropospheric warming over the r...

Interannual Coupling between Summertime Surface Temperature and Precipitation over Land: Processes and Implications for Climate Change*

Widespread negative correlations between summertime-mean temperatures and precipitation over land regions are a well-known feature of terrestrial climate. This behavior has generally been interpreted in the context of soil moisture atmosphere coupling, with soil moisture deficits associated with reduced rainfall leading to enhanced surface sensible heating and higher surface temperature. The present study revisits the genesis of these negative temperature precipitation correlations using simulations from the Global Land Atmosphere Coupling Experiment phase 5 of the Coupled Model Intercomparison Project (GLACE-CMIP5) multimodel experiment. The analyses are based on simulations with five climate models, which were integrated with prescribed (noninteractive) and with interactive soil moisture over the period 1950-2100. While the results presented here generally confirm the interpretation that negative correlations between seasonal temperature and precipitation arise through the direct control of soil moisture on surface heat flux partitioning, the presence of widespread negative correlations when soil moisture atmosphere interactions are artificially removed in at least two out of five models suggests that atmospheric processes, in addition to land surface processes, contribute to the observed negative temperature precipitation correlation. On longer time scales, the negative correlation between precipitation and temperature is shown to have implications for the projection of climate change impacts on near-surface climate: in all models, in the regions of strongest temperature precipitation anticorrelation on interannual time scales, long-term regional warming is modulated to a large extent by the regional response of precipitation to climate change, with precipitation increases (decreases) being associated with minimum (maximum) warming. This correspondence appears to arise largely as the result of soil moisture atmosphere interactions.

Impact of Soil Moisture–Atmosphere Interactions on Surface Temperature Distribution

AbstractUnderstanding how different physical processes can shape the probability distribution function (PDF) of surface temperature, in particular the tails of the distribution, is essential for the attribution and projection of future extreme temperature events. In this study, the contribution of soil moisture–atmosphere interactions to surface temperature PDFs is investigated. Soil moisture represents a key variable in the coupling of the land and atmosphere, since it controls the partitioning of available energy between sensible and latent heat flux at the surface. Consequently, soil moisture variability driven by the atmosphere may feed back onto the near-surface climate—in particular, temperature. In this study, two simulations of the current-generation Geophysical Fluid Dynamics Laboratory (GFDL) Earth System Model, with and without interactive soil moisture, are analyzed in order to assess how soil moisture dynamics impact the simulated climate. Comparison of these simulations shows that soil moist...

The delayed effect of major El Niño events on Indian monsoon rainfall.

Abstract Previous studies have shown that boreal summer Indian monsoon rainfall is, on average, significantly above normal after major El Nino events. In this study, the underlying causes of this rainfall response are examined using both observational analysis and atmospheric general circulation model (AGCM) simulations. Moist static energy budgets for two strong El Nino events (1982/83 and 1997/98), estimated from monthly 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-40), suggest that stronger low-level moisture transport and reduced moist stability associated with a warmer north Indian Ocean (NIO) can increase monsoon rainfall, despite a weakened monsoon circulation. The trade-off between a dynamically weaker monsoon and moist processes favoring enhanced monsoonal rainfall is broken during the late monsoon season (August–September) as the warm NIO enhances surface latent heat flux and the monsoon circulation relaxes back to the climatological mean. The monsoon circulation str...

Precipitation Sensitivity to Surface Heat Fluxes over North America in Reanalysis and Model Data

A new methodology for assessing the impact of surface heat fluxes on precipitation is applied to data from the North American Regional Reanalysis (NARR) and to output from the Geophysical Fluid Dynamics Laboratory’s Atmospheric Model 2.1 (AM2.1). The method assesses the sensitivity of afternoon convective rainfall frequency and intensity to the late-morning partitioning of latent and sensible heating, quantified in terms of evaporative fraction (EF). Over North America, both NARR and AM2.1 indicate sensitivity of convective rainfall triggering to EF but no appreciable influence of EF on convective rainfall amounts. Functional relationships between the triggering feedback strength (TFS) metric and mean EF demonstrate the occurrence of stronger couplingfor meanEFintherangeof0.6to 0.8. To leadingorder, AM2.1exhibits spatial distributions and seasonality of the EF impact on triggering resembling those seen in NARR: rainfall probability increases with higher EF over the eastern United States and Mexico and peaks in Northern Hemisphere summer. Over those regions, the impact of EF variability on afternoon rainfall triggering in summer can explain up to 50% of seasonal rainfall variability. However, the AM2.1 metrics also exhibit some features not present in NARR, for example, strong coupling extending northwestward from the central Great Plains into Canada. Sources of disagreement may include model hydroclimatic biases that affect the mean patterns and variability of surface flux partitioning, withEF variability typically much lower in NARR. Finally, the authors also discuss the consistency of their results with other assessments of land‐precipitation coupling obtained from different methodologies.

A Probabilistic Bulk Model of Coupled Mixed Layer and Convection. Part II: Shallow Convection Case

The probabilistic bulk convection model (PBCM) developed in a companion paper is here extended to shallow nonprecipitating convection. The PBCM unifies the clear-sky and shallow convection boundary layer regimes by obtaining mixed-layer growth, cloud fraction, and convective inhibition from a single parameterization based on physical principles. The evolution of the shallow convection PBCM is based on the statistical distribution of the surface thermodynamic state of convective plumes. The entrainment velocity of the mixed layer is related to the mass flux of the updrafts overshooting the dry inversion capping the mixed layer. The updrafts overcoming the convective inhibition generate active cloudbase mass flux, which is the boundary condition for the shallow cumulus scheme. The subcloud-layer entrainment velocity is directly coupled to the cloud-base mass flux through the distribution of vertical velocity and fractional cover of the updrafts. Comparisons of the PBCM against large-eddy simulations from the Barbados Oceanographic and MeteorologicalExperiment (BOMEX) andfromthe SouthernGreat PlainsAtmospheric RadiationMeasurement Program (ARM) facility demonstrate good agreement in terms of thermodynamic structure, cloud-base mass flux, and cloud top. The equilibrium between the cloud-base mass flux and rate of growth of the mixed layer determines the equilibrium convective inhibition and cloud cover. This process is an important new insight on the coupling between the mixed-layer and cumulus dynamics. Given its relative simplicity and transparency, the PBCM represents a powerful tool for developing process-based understanding and intuition about the physical processes involved in boundary layer–convection interactions, as well as a test bed for diagnosing and validating shallow convection parameterizations.

Adjustment of the remote tropical climate to El Niño conditions

Abstract The adjustment of the tropical climate outside the Pacific (the “remote Tropics”) to the abrupt onset of El Nino conditions is examined in a tropical atmosphere model that assumes simplified vertical structure and quasi-equilibrium (QE) convective closure. The El Nino signal is rapidly (∼1 week) communicated to the remote Tropics via an eastward-propagating Kelvin-like wave that induces both anomalous subsidence and tropospheric warming. Widespread reductions in convective precipitation occur in conjunction with the spreading of the temperature and subsidence anomalies. The remote rainfall suppression peaks roughly 5–15 days after the initiation of El Nino conditions, after which the anomalous remote rainfall field recovers to a state characterized by a smaller remote areal mean rainfall deficit and the appearance of localized positive rainfall anomalies. The initial remote precipitation reduction after El Nino onset is tied to both tropospheric warming (i.e., stabilization of the troposphere to ...

Deep Convection and Column Water Vapor over Tropical Land versus Tropical Ocean: A Comparison between the Amazon and the Tropical Western Pacific

AbstractThe relationships between the onset of tropical deep convection, column water vapor (CWV), and other measures of conditional instability are analyzed with 2 yr of data from the DOE Atmospheric Radiation Measurement (ARM) Mobile Facility in Manacapuru, Brazil, as part of the Green Ocean Amazon (GOAmazon) campaign, and with 3.5 yr of CWV derived from global positioning system meteorology at a nearby site in Manaus, Brazil. Important features seen previously in observations over tropical oceans—precipitation conditionally averaged by CWV exhibiting a sharp pickup at high CWV, and the overall shape of the CWV distribution for both precipitating and nonprecipitating points—are also found for this tropical continental region. The relationship between rainfall and CWV reflects the impact of lower-free-tropospheric moisture variability on convection. Specifically, CWV over land, as over ocean, is a proxy for the effect of free-tropospheric moisture on conditional instability as indicated by entraining plu...

Column Water Vapor Statistics and Their Relationship to Deep Convection, Vertical and Horizontal Circulation, and Moisture Structure at Nauru

AbstractRelationships among relatively high-frequency probability distribution functions (pdfs) of anomalous column water vapor (cwv), precipitating deep convection, and the vertical and horizontal structures of circulation and tropospheric moisture are investigated for the Atmospheric Radiation Measurement (ARM) climate observing facility at Nauru in the western equatorial Pacific. At the highest frequencies (subdaily) analyzed, the cwv pdf exhibits a Gaussian core with pronounced longer-than-Gaussian, approximately exponential tails, with the relatively lower-frequency submonthly pdfs becoming more Gaussian distributed across the entire range of cwv variability. The genesis and morphology of the longer-than-Gaussian tails are examined within the context of several hypothetical mechanisms outlined in prior work. For example, pdf conditioning on ARM optical gauge precipitation measurements reveals an association of the positive-side tail with precipitating deep convective conditions; thus, despite the con...