[1] We analyze the relation between atmospheric temperature and water vapor-a fundamental component of the global climate system-for stratospheric water vapor (SWV). We compare measurements of SWV (and methane where available) over the period 1980-2011 from NOAA balloon-borne frostpoint hygrometer (NOAA-FPH), SAGE II, Halogen Occultation Experiment (HALOE), Microwave Limb Sounder (MLS)/Aura, and Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) to model predictions based on troposphere-to-stratosphere transport from ERA-Interim, and temperatures from ERA-Interim, Modern Era Retrospective-Analysis (MERRA), Climate Forecast System Reanalysis (CFSR), Radiosonde Atmospheric Temperature Products for Assessing Climate (RATPAC), HadAT2, and RICHv1.5. All model predictions are dry biased. The interannual anomalies of the model predictions show periods of fairly regular oscillations, alternating with more quiescent periods and a few large-amplitude oscillations. They all agree well (correlation coefficients 0.9 and larger) with observations for higherfrequency variations (periods up to 2-3 years). Differences between SWV observations, and temperature data, respectively, render analysis of the model minus observation residual difficult. However, we find fairly well-defined periods of drifts in the residuals. For the 1980s, model predictions differ most, and only the calculation with ERA-Interim temperatures is roughly within observational uncertainties. All model predictions show a drying relative to HALOE in the 1990s, followed by a moistening in the early 2000s. Drifts to NOAA-FPH are similar (but stronger), whereas no drift is present against SAGE II. As a result, the model calculations have a less pronounced drop in SWV in 2000 than HALOE. From the mid-2000s onward, models and observations agree reasonably, and some differences can be traced to problems in the temperature data. These results indicate that both SWV and temperature data may still suffer from artifacts that need to be resolved in order to answer the question whether the large-scale flow and temperature field is sufficient to explain water entering the stratosphere. Citation: Fueglistaler, S., et al. (2013), The relation between atmospheric humidity and temperature trends for stratospheric water,

The comparison of trends in various climate indices in observations and models is of fundamental importance for judging the credibility of climate projections. Tropical tropospheric temperature trends have attracted particular attention as this comparison may suggest a model deficiency. One can think of this problem as composed of two parts: one focused on tropical surface temperature trends and the associated issues related to forcing, feedbacks, and ocean heat uptake and a second part focusing on connections between surface and tropospheric temperatures and the vertical profile of trends in temperature. Here we focus on the atmospheric component of the problem. We show that two ensembles of Geophysical Fluid Dynamics Laboratory HiRAM model runs (similar results are shown for National Center for Atmospheric Research's CAM4 model) with different commonly used prescribed sea surface temperatures (SSTs), namely, the HadISST1 and "Hurrell" data sets, have a difference in upper tropical tropospheric temperature trends (∼0.1 K/decade at 300 hPa for the period ) that is about a factor 3 larger than expected from moist adiabatic scaling of the tropical average SST trend difference. We show that this surprisingly large discrepancy in temperature trends is a consequence of SST trend differences being largest in regions of deep convection. Further, trends, and the degree of agreement with observations, not only depend on SST data set and the particular atmospheric temperature data set but also on the period chosen for comparison. Due to the large impact on atmospheric temperatures, these systematic uncertainties in SSTs need to be resolved before the fidelity of climate models' tropical temperature trend profiles can be assessed.

[1] We analyze the propagation of equatorial Kelvin waves from the troposphere to the stratosphere using a new filtering technique applied to ERA-Interim data (very similar results for Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) temperatures) that allows separation of wave activity into number of waves and wave amplitude. The phase speed of Kelvin waves (order 20 m/s) is similar to the magnitude of zonal wind in the tropical tropopause layer (TTL), and correspondingly, we find that the seasonal and interannual variability of Kelvin wave propagation is dominated by the variability in the wind field and less by tropospheric convectively coupled wave activity. We show that local relations between wave activity and zonal wind are ambiguous, and only full ray tracing calculations can explain the observed patterns of wave activity. Easterlies amplify and deflect the eastward traveling waves upward. Westerlies have the opposite effect. During boreal winter, the strong dipole of zonal winds in the TTL centered at the dateline confines wave propagation into the stratosphere to a window over the Atlantic-Indian Ocean sector (30°W to 90°E), which casts a lasting "shadow" into the lower stratosphere that explains the remarkable zonal asymmetry in wave activity there. During boreal summer, the upper level monsoon circulation leads to maximum easterlies, and wave amplitude (but not number of waves) maximizes over the Indian Ocean sector (30°E to 90°E). Interannual variability in wave propagation due to El-Niño/Southern Oscillation, for example, is well explained by its modification of the zonal wind field.

It has been suggested that the tropical tropopause layer (TTL) may be affected by mixing from shear‐flow instability in connection with Kelvin waves. It is shown that the revised Louis‐scheme (used in operational analyses and ERA‐40 and ERA‐Interim of ECMWF) strongly responds to Kelvin wave perturbations, and average mixing is maximized where Kelvin wave amplitudes are largest (Indian ocean/Maritime continent). Conversely, the Monin‐Obukhov scheme predicts fewer, but more intense mixing events that maximize further East. For the TTL, the mixing predicted by the two schemes is similar and small, but locally the models predict shear‐flow mixing sufficient to yield net diabatic descent over the aforementioned regions. The data analyzed here remains inconclusive about which scheme captures reality better, rendering the role of Kelvin waves for shear‐flow instability uncertain. The mixing schemes' sensitivity to Kelvin waves has implications for the dissipation of Kelvin waves in models and analyzed meteorological data.

[1] Convectively coupled Kelvin waves in the troposphere have a vertically propagating component which propagates through the tropical tropopause layer into the stratosphere. In the tropical tropopause layer above the typical top of deep convection, these waves propagate as dry waves. In the stratosphere they contribute to the forcing of the stratospheric quasi-biennial oscillation. Here, we address the challenge to track individual waves in a region where both static stability and background wind rapidly change with a new algorithm that operates in real space and uses the full longitude/height/time information available to reliably identify Kelvin waves. We argue that our algorithm overcomes inherent ambiguities in previously published methods. Specifically, our algorithm cleanly separates wave activity and number of waves, and successfully tracks waves also in regions where background wind reduces wave amplitudes. Applied to ECMWF reanalysis data for the period 1989-2011, we obtain a statistical description of Kelvin wave propagation that shows propagation through the TTL into the stratosphere occurs predominantly over the Indian Ocean and Atlantic.Citation: Flannaghan, T. J., and S. Fueglistaler (2012), Tracking Kelvin waves from the equatorial troposphere into the stratosphere,