Summary for policymakers Technical summary 1. The climate system - an overview 2. Observed climate variability and change 3. The carbon cycle and atmospheric CO2 4. Atmospheric chemistry and greenhouse gases 5. Aerosols, their direct and indirect effects 6. Radiative forcing of climate change 7. Physical climate processes and feedbacks 8. Model evaluation 9. Projections of future climate change 10. Regional climate simulation - evaluation and projections 11. Changes in sea level 12. Detection of climate change and attribution of causes 13. Climate scenario development 14. Advancing our understanding Glossary Index Appendix.

Climate change 2001: the scientific basis

This paper describes the contents of the 2016 edition of the HITRAN molecular spectroscopic compilation. The new edition replaces the previous HITRAN edition of 2012 and its updates during the intervening years. The HITRAN molecular absorption compilation is composed of five major components: the traditional line-by-line spectroscopic parameters required for high-resolution radiative-transfer codes, infrared absorption cross-sections for molecules not yet amenable to representation in a line-by-line form, collision-induced absorption data, aerosol indices of refraction, and general tables such as partition sums that apply globally to the data. The new HITRAN is greatly extended in terms of accuracy, spectral coverage, additional absorption phenomena, added line-shape formalisms, and validity. Moreover, molecules, isotopologues, and perturbing gases have been added that address the issues of atmospheres beyond the Earth. Of considerable note, experimental IR cross-sections for almost 300 additional molecules important in different areas of atmospheric science have been added to the database. The compilation can be accessed through www.hitran.org. Most of the HITRAN data have now been cast into an underlying relational database structure that offers many advantages over the long-standing sequential text-based structure. The new structure empowers the user in many ways. It enables the incorporation of an extended set of fundamental parameters per transition, sophisticated line-shape formalisms, easy user-defined output formats, and very convenient searching, filtering, and plotting of data. A powerful application programming interface making use of structured query language (SQL) features for higher-level applications of HITRAN is also provided.

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The HITRAN 2008 molecular spectroscopic database

Clouds and Aerosols

A new version of the atmosphere–ocean general circulation model cooperatively produced by the Japanese research community, known as the Model for Interdisciplinary Research on Climate (MIROC), has recently been developed. A century-long control experiment was performed using the new version (MIROC5) with the standard resolution of the T85 atmosphere and 1° ocean models. The climatological mean state and variability are then compared with observations and those in a previous version (MIROC3.2) with two different resolutions (medres, hires), coarser and finer than the resolution of MIROC5. A few aspects of the mean fields in MIROC5 are similar to or slightly worse than MIROC3.2, but otherwise the climatological features are considerably better. In particular, improvements are found in precipitation, zonal mean atmospheric fields, equatorial ocean subsurface fields, and the simulation of El Nino–Southern Oscillation. The difference between MIROC5 and the previous model is larger than that between th...

/pdf/improved-climate-simulation-by-miroc5-mean-states-yovp0f6kr1.pdf

Improved Climate Simulation by MIROC5: Mean States, Variability, and Climate Sensitivity

[1] Arctic amplification (AA) – the observed enhanced warming in high northern latitudes relative to the northern hemisphere – is evident in lower-tropospheric temperatures and in 1000-to-500 hPa thicknesses. Daily fields of 500 hPa heights from the National Centers for Environmental Prediction Reanalysis are analyzed over N. America and the N. Atlantic to assess changes in north-south (Rossby) wave characteristics associated with AA and the relaxation of poleward thickness gradients. Two effects are identified that each contribute to a slower eastward progression of Rossby waves in the upper-level flow: 1) weakened zonal winds, and 2) increased wave amplitude. These effects are particularly evident in autumn and winter consistent with sea-ice loss, but are also apparent in summer, possibly related to earlier snow melt on high-latitude land. Slower progression of upper-level waves would cause associated weather patterns in mid-latitudes to be more persistent, which may lead to an increased probability of extreme weather events that result from prolonged conditions, such as drought, flooding, cold spells, and heat waves.

The linear response function of an idealized atmosphere. Part 1: Construction using Green's functions and applications

The linear response function (LRF) of an idealized GCM, the dry dynamical core with Held-Suarez physics, is used to accurately compute how eddy momentum and heat fluxes change in response to the zonal wind and temperature anomalies of the annular mode at the low-frequency limit Using these results and knowing the parameterizations of surface friction and thermal radiation in Held-Suarez physics, the contribution of each physical process (meridional and vertical eddy fluxes, surface friction, thermal radiation, and meridional advection) to the annular mode dynamics is quantified Examining the quasi-geostrophic potential vorticity balance, it is shown that the eddy feedback is positive and increases the persistence of the annular mode by a factor of more than two Furthermore, how eddy fluxes change in response to only the barotropic component of the annular mode, ie, vertically averaged zonal wind (and no temperature) anomaly, is also calculated similarly The response of eddy fluxes to the barotropic-only component of the annular mode is found to be drastically different from the response to the full (barotropic+baroclinic) annular mode anomaly In the former, the barotropic governor effect significantly suppresses the eddy generation leading to a negative eddy feedback that decreases the persistence of the annular mode by nearly a factor of three These results suggest that the baroclinic component of the annular mode anomaly, ie, the increased low-level baroclinicity, is essential for the persistence of the annular mode, consistent with the baroclinic mechanism but not the barotropic mechanism proposed in the previous studies

Quantifying the annular mode dynamics in an idealized atmosphere

Precipitation and storm track activity in the Southern Hemisphere feature a remarkable 20 to 30-day periodicity known as baroclinic annular mode. In climate model projections following the representative concentration pathway 8.5 scenario, this work finds a robust increase of intraseasonal variability of the precipitation and density-weighted eddy kinetic energy at the 20–30 day frequency range by 25% and 20%, respectively, in austral summer toward the end of the century, despite small changes in seasonal-mean quantities at corresponding latitudes. These results suggest that a warming climate can feature a stronger dynamical organization of the 20–30 day periodicity by the moist baroclinic waves. For austral winter, the weak 20–30 day periodicity in the current climate becomes a prominent mode of quasiperiodic variability toward the end of the century in these model projections. This work identifies both the increase of diabatic heating and the enhancements of the waveguide effects as candidate mechanisms. Plain Language Summary This work reports a robust increase of the intraseasonal periodic behavior in the Southern Hemisphere storm track with important implications on midlatitude hydrological extremes. While it is well-documented that the jet stream will shift poleward in a warming climate, this is the first contribution that identifies how the intraseasonal variability of the storm tracks would change in response to global warming in comprehensive climate models (National Center for Atmospheric Research Large Ensemble project and CMIP5 outputs). Evidence suggests that both the increase of moisture and the change of a climatological basic state can contribute to the intensification of the intraseasonal variability, which implies a more predictable baroclinic annular mode in the Southern Hemisphere in a warmer climate. This finding serves as a stimulus for future studies to unveil the role of changing diabatic heating on the intraseasonal variability in the midlatitudes.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2018GL078495

A Robust Increase of the Intraseasonal Periodic Behavior of the Precipitation and Eddy Kinetic Energy in a Warming Climate

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2019GL082089

A Moist Entropy Budget View of the South Asian Summer Monsoon Onset

Previous studies have documented that deep convection responds more strongly to above-the-cloud-base temperature perturbations in the lower troposphere than to those in the upper tropospher...

https://journals.ametsoc.org/doi/pdf/10.1175/JAS-D-18-0023.1

Zhiming Kuang

Papers

The linear response function of an idealized atmosphere. Part 1: Construction using Green's functions and applications

Quantifying the annular mode dynamics in an idealized atmosphere

A Robust Increase of the Intraseasonal Periodic Behavior of the Precipitation and Eddy Kinetic Energy in a Warming Climate

A Moist Entropy Budget View of the South Asian Summer Monsoon Onset

Why Does Deep Convection Have Different Sensitivities to Temperature Perturbations in the Lower versus Upper Troposphere