Relationship between the expansion of drylands and the intensification of Hadley circulation during the late twentieth century

The changes in coverage by arid climate and intensity of the Hadley circulation during the second half of the twentieth century were examined using observations and the multi-model ensemble (MME) mean of Twentieth-Century Coupled Climate Model (20C3M) simulations. It was found that the area of dry climate, which comprises steppe and desert climates following the Köppen climate classification, expanded to an appreciable extent in observation and, to a lesser degree, in MME simulation. The areal extent of steppe climate (the outer boundary of arid climate) tends to encroach on the surrounding climate groups, which, in turn, feeds desert climate (the inner part of arid climate) and causes it to grow. This result indicates the importance of accurate prediction for climate regimes that border steppe climate. Concomitant with the expansion of drylands, the observed intensity of the Hadley cell is persistently enhanced, particularly during boreal winter, suggesting the validity of a self-induction of deserts through a positive biogeophysical feedback (also known as Charney’s cycle). In comparison, the simulated Hadley circulation in the MME mean remains invariant in time. The current climate models, therefore, disagree with the observation in the long-term linkage between desertification and Hadley cell. Finally, the implication of such discrepancy is discussed as a possible guidance to improve models

Computation of Solar Radiative Fluxes by 1D and 3D Methods Using Cloudy Atmospheres Inferred from A-train Satellite Data

The main point of this study was to use realistic representations of cloudy atmospheres to assess errors in solar flux estimates associated with 1D radiative transfer models. A scene construction algorithm, developed for the EarthCARE satellite mission, was applied to CloudSat, CALIPSO, and MODIS satellite data thus producing 3D cloudy atmospheres measuring 60 km wide by 13,000 km long at 1 km grid-spacing. Broadband solar fluxes and radiances for each (1 km)2 column where then produced by a Monte Carlo photon transfer model run in both full 3D and independent column approximation mode (i.e., a 1D model)

Water balance creates a threshold in soil pH at the global scale

Soil pH regulates the capacity of soils to store and supply nutrients, and thus contributes substantially to controlling productivity in terrestrial ecosystems. However, soil pH is not an independent regulator of soil fertility-rather, it is ultimately controlled by environmental forcing. In particular, small changes in water balance cause a steep transition from alkaline to acid soils across natural climate gradients. Although the processes governing this threshold in soil pH are well understood, the threshold has not been quantified at the global scale, where the influence of climate may be confounded by the effects of topography and mineralogy. Here we evaluate the global relationship between water balance and soil pH by extracting a spatially random sample (n = 20,000) from an extensive compilation of 60,291 soil pH measurements. We show that there is an abrupt transition from alkaline to acid soil pH that occurs at the point where mean annual precipitation begins to exceed mean annual potential evapotranspiration. We evaluate deviations from this global pattern, showing that they may result from seasonality, climate history, erosion and mineralogy. These results demonstrate that climate creates a nonlinear pattern in soil solution chemistry at the global scale; they also reveal conditions under which soils maintain pH out of equilibrium with modern climate

Application of deep convective cloud albedo observation to satellite-based study of the terrestrial atmosphere: Monitoring the stability of spaceborne measurements and assessing absorption anomaly

An objective method is developed to monitor the stability of spaceborne instruments, aimed at distinguishing climate trend from instrument drift in satellite-based climate observation records. This method is based on four-years of Clouds and the Earth's Radiant Energy System (CERES) broadband observations of deep convective cloud systems with cloud-top temperature lower than 205 K and with large optical depths. The implementation of this method to the CERES instrument stability analysis reveals that the monthly albedo distributions are practically the same for deep convective clouds with CERES measurements acquired from both the Tropical Rainfall Measuring Mission and Terra satellite platforms, indicating that CERES instruments are well calibrated and stable during both missions. Furthermore, with a nonlinear regression neural network narrowband-broadband conversion, this instrument-stability monitoring method can also be applied to narrowband instruments such as the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Visible Infrared Scanner (MRS). The results show that the drifts associated with both VIRS and MODIS instruments are less than 1% during a four-year period. Since the CERES albedo measurements are highly accurate, the absorptance of these opaque clouds can be reliably estimated. The absorptions of these clouds from observations are around 25%, whereas the absorptions from theory can be as low as 18%, depending on ice cloud microphysics.link_to_subscribed_fulltex