Explore the vast range of titles available.

Tropics nurture three different types of convective clouds, i.e., shallow cumulus, cumulus congestus, and deep cumulonimbus. The vertical structure of clouds holds a crucial metric in studying tropical clouds. Ground-based high-resolution cloud radar measurements are the potential candidate in exploring the characteristics of various types of tropical clouds and their evolution. Quality-controlled cloud radar data containing a total of five million vertical profiles of equivalent reflectivity factor (VPR) are used to examine the intra-seasonal variation of cloud vertical structure (VSC) during the Indian summer monsoon (ISM) over Mandhardev (18.04° N, 73.87° E, and ~ 1.3 km AMSL) in the Indian Western Ghats. The cumulus congestus (Cc) in the transition of shallow to deep clouds is investigated for the first time using the hourly VPR data for 60 consecutive ISM days. Mid-level moistening plays a vital role in this non-precipitating shallow to precipitating congestus transformation and increment of the rain accumulation. Low cloud reflectivity distribution can distinguish precipitating and non-precipitating clouds that help to classify the observed monsoon as normal or below normal. More than 150 mm of rain accumulation during ISM is associated with more than 22% of high clouds. This particular aspect indicates that cold rain processes are essential to assess the ISM over the observational site. FFT analysis on the time series of low-, mid-, and high-level cloud regions with the VPR shows prominent intra-seasonal variability of 5–10, 10–20, and 30–60 days periodicities. This study highlights the significance of VSC over tropics pertinent to the monsoon large scale atmospheric condition.

General circulation models frequently suffer from a substantial cold bias in equatorial Pacific sea surface temperatures (SSTs). For instance, the majority of the climate models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) have this particular problem (17 out of the 26 models evaluated in the present study). Here, we investigate the extent to which these equatorial cold biases are related to mean climate biases generated in the extra-tropics and then communicated to the equator via the oceanic subtropical cells (STCs). With an evident relationship across the CMIP5 models between equatorial SSTs and upper ocean temperatures in the extra-tropical subduction regions, our analysis suggests that cold SST biases within the extra-tropical Pacific indeed translate into a cold equatorial bias via the STCs. An assessment of the relationship between these extra-tropical SST biases and local surface heat flux components indicates a link to biases in the simulated shortwave fluxes. Further sensitivity studies with a climate model (CESM) in which extra-tropical cloud albedo is systematically varied illustrate the influence of cloud albedo perturbations, not only directly above the oceanic subduction regions but across the extra-tropics, on the equatorial bias. The CESM experiments reveal a quadratic relationship between extra-tropical Pacific albedo and the root-mean-square-error in equatorial SSTs—a relationship with which the CMIP5 models generally agree. Thus, our study suggests that one way to improve the equatorial cold bias in the models is to improve the representation of subtropical and mid-latitude cloud albedo.

Tropical low‐cloud feedback is the largest source of uncertainty in climate sensitivity, yet multi‐century records of surface shortwave radiation are scarce. We calibrate Porites coral δ13C against satellite photosynthetically available radiation (PAR) and reconstruct monthly PAR for the northern South China Sea during the Medieval Climate Anomaly (1129–1264 CE) and the Little Ice Age (1631–1771 CE). After correcting for the Suess effect and propagating errors via Monte Carlo resampling techniques, annual PAR during the Little‐Ice‐Age is ∼22% lower and seasonality slightly weaker. The dimming aligns with regional proxies for cooler, wetter conditions and is best explained by brighter low clouds, likely boosted by volcanic aerosol–cloud interactions. CMIP6/PMIP4 past1000 simulations, however, yield <0.2% change over the same interval, indicating that current models understate volcanic microphysics and tropical low‐cloud sensitivity. The coral PAR record thus provides a quantitative pre‐industrial target for evaluating tropical cloud processes and reducing uncertainty in equilibrium climate sensitivity.

Tropical cloud clusters (TCCs) play a critical role in sustaining tropical large-scale systems and are traditionally viewed as precursors for tropical cyclone (TC) genesis. This study focuses on the decadal changes in genesis productivity (GP), e.g. the efficiency of TCCs developing into TCs, and shows a significant decrease in GP over the western North Pacific (WNP) basin since 1998, when a climate regime change occurred. The significant decrease in TC frequency and the significant increase in TCCs, especially over the eastern region of the WNP basin, have combined to result in a reduced GP since 1998. These changes are dependent on the combined changes in large-scale atmospheric-oceanic conditions over the WNP basin. A decadal change in vertical wind shear, especially over the eastern portion of the WNP basin, appears to be the most important contributor to the recent decrease in GP. Increased vertical wind shear suppresses TC genesis but enhances the frequency of TCCs. Secondary positive contributions to the recent decrease in GP are from local sea surface temperatures (SSTs) and low-level relative vorticity. These positive contributions to the recent decrease in GP are partly cancelled out by a negative contribution from enhanced mid-relative moisture. Changes in these large-scale conditions associated with the recent decrease in GP over the WNP basin since 1998 are closely related to the weakening monsoon circulation and the westward shift of the tropical upper-tropospheric trough over the WNP. This is likely related to the changes observed in tropical SST anomalies around the globe.

Understanding the role of tropical cloud clusters (TCC) in the development of tropical cyclones involves various complexities and, thus, necessitates precise research. The study on TC development from the TCCs is still minimal. The present research is carried out to investigate the predictability of Tropical cyclogenesis (TCG) by examining the Rossby Radius Ratio (RRR) and Daily Genesis Potential (DGP) of different cloud clusters over the four ocean basins in the Northern Hemisphere, viz., North Indian Ocean (NIO), North Atlantic Ocean (NAO), West Pacific Ocean (WPO), and East Pacific Ocean (EPO). The analysis of the TCC data, taken for the period 1996–2005, shows that both the predictors are skilled at identifying the developed and non-developed TCCs. The method of cumulative distribution is implemented to identify the threshold ranges of RRR and DGP. In addition, the forecast skill scores are estimated for the selected predictors. The rough set theory based on different condition-decision support is implemented to estimate the certainty in the TCG prediction scheme with each predictor individually and in combination. The result shows that higher certainty in TCG prediction is observed when RRR ≤ 24 and DGP ≥ 1.21 × 10−5 for the NIO basin. However, it is to be noted that the combination of both RRR and DGP provides better confidence in the predictability of TCG over the NAO basin (RRR ≤ 38 and DGP ≥ 0.71 × 10−5) and EPO basin (RRR ≤ 28.7 and DGP ≥ 0.47 × 10−5). Furthermore, RRR (threshold value ≤ 28.2) individually gives better predictability for TCG over the WPO basin. The forecasts of TCG with RRR and DGP are validated with the observations from 2006 to 2009.

The underestimation of cloud fraction, especially the low stratus cloud (LSC) fraction over the eastern oceans, remains a problem in most atmospheric global climate models. This study investigated potential improvements through perturbing nine moist physical parameters, using uniform sampling and Latin hypercube sampling methods, and quantified the parametric uncertainty and effects of non‐linear interaction between parameters on the tropical cloud fraction in the Grid‐Point Atmospheric Model of the Institute of Atmospheric Physics/State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, version 2. Results showed that the uncertainty ranges of the tropical total cloud fraction and LSC associated with multiple‐parameter perturbation were larger than those from any single‐parameter perturbation. The total cloud fraction was significantly improved with multiple‐parameter perturbation and the LSC also increased notably when using parameter values optimized for the total cloud fraction because of the indirect parametric effect on lower‐tropospheric stability. Non‐linear effects between parameters on simulating LSC were much stronger than those on simulating the total cloud fraction. Furthermore, the non‐linear interaction reduced large values of total cloud fraction but had a strong incremental effect on large values of LSC over the southeast Pacific. The findings demonstrate the feasibility of improving the simulation of LSC over the eastern oceans by tuning moist parameters, and provide further insight into the non‐linear effects between parameters on the simulation of cloud fraction. Plain Language Summary Clouds play a crucial role in Earth's climate system by modulating radiation budgets. This paper reports the results of a study aimed at better understanding the moist parametric uncertainty and non‐linear effects on the tropical cloud fraction in climate model simulations. This is important because underestimation of the tropical cloud fraction—particularly over marine stratus regions—remains a problem for climate models. Determining whether the biases can be reduced by tuning parameters may provide a solution. Our results demonstrate the feasibility of improving the simulation of total cloud fraction, and even marine stratus, through parameter tuning. Furthermore, our results highlight the different non‐linear effects on cloud over different areas, which should motivate further studies on these non‐linear effects within other important physical processes or phenomena in climate simulations. Key Points Two methods are used to quantify the parametric uncertainty and non‐linear effects between parameters on tropical cloud fraction The total cloud fraction is improved and the marine stratus also increases because of the indirect parametric effect on lower‐tropospheric stability The effects of non‐linear interaction between parameters on the marine stratus are stronger than those on the total cloud fraction

Foliar water uptake (FWU) is a common water acquisition mechanism for plants inhabiting temperate fog-affected ecosystems, but the prevalence and consequences of this process for the water and carbon balance of tropical cloud forest species are unknown. We performed a series of experiments under field and glasshouse conditions using a combination of methods (sap flow, fluorescent apoplastic tracers and stable isotopes) to trace fog water movement from foliage to belowground components of Drimys brasiliensis. In addition, we measured leaf water potential, leaf gas exchange, leaf water repellency and growth of plants under contrasting soil water availabilities and fog exposure in glasshouse experiments to evaluate FWU effects on the water and carbon balance of D. brasiliensis saplings. Fog water diffused directly through leaf cuticles and contributed up to 42% of total foliar water content. FWU caused reversals in sap flow in stems and roots of up to 26% of daily maximum transpiration. Fog water transported through the xylem reached belowground pools and enhanced leaf water potential, photosynthesis, stomatal conductance and growth relative to plants sheltered from fog. Foliar uptake of fog water is an important water acquisition mechanism that can mitigate the deleterious effects of soil water deficits for D. brasiliensis.

Soil and water characteristics in micro basins with different land uses/land cover (LULC) can influence riparian vegetation diversity, stream water quality, and benthic diatom diversity. We analyzed 18 streams in the upper part of the La Antigua River basin, México, surrounded by cloud forests, livestock pastures, and coffee plantations. Concentrations of P, C, and N were elevated in the humus of forested streams compared to other land uses. In contrast, cations, ammonium, and total suspended solids (TSS) of water streams were higher in pastures and coffee plantations. These results indicate that LULC affects stream chemistry differently across land uses. Vegetation richness was highest (86–133 spp.) in forest streams and lowest in pastures (46–102), whereas pasture streams had the greatest richness of diatoms (9–24), likely due to higher light and temperatures. Some soil and water characteristics correlated with both true diversity and taxonomic diversity; soil carbon exchange capacity (CEC) correlated with vegetation diversity ( r  = 0.60), while water temperature correlated negatively ( r  =  − 0.68). Diatom diversity was related to soil aluminum ( r  =  − 0.59), magnesium ( r  = 0.57), water phosphorus ( r  = 0.88), and chlorophyll ( r  = 0.75). These findings suggest that land use affects riparian vegetation, while physical and chemical changes influence diatom diversity in stream water and soil. The lack of correlation between vegetation and diatom diversity indicates that one cannot predict the other. This research is an essential first step in understanding how land use changes impact vegetation and diatom diversity in mountain landscapes, providing valuable insights for environmental monitoring and conservation efforts in tropical cloud forests.

Tropical cloud clusters (TCCs) are embryos of tropical cyclones (TCs) and may have the potential to develop into TCs. The genesis productivity (GP) of TCCs is used to quantify the proportion of TCCs that can evolve into TCs. Recent studies have revealed a decrease in GP of western North Pacific (WNP) TCCs during the extended boreal summer (July–October) since 1998. Here, we show that the changing tendencies in GP of WNP TCCs have obvious seasonality. Although most months could see recent decreases in GP of WNP TCCs, with October experiencing the strongest decreasing trend, May is the only month with a significant recent increasing trend. The opposite changing tendencies in May and October could be attributed to different changes in low-level atmospheric circulation anomalies triggered by different sea surface temperature (SST) configurations across the tropical oceans. In May, stronger SST warming in the tropical western Pacific could prompt increased anomalous westerlies associated with anomalous cyclonic circulation, accompanied by the weakening of the WNP subtropical high and the strengthening of the WNP monsoon. Such changes in background atmospheric circulations could favor the enhancement of atmospheric eddy kinetic energy and barotropic energy conversions, resulting in a recent intensified GP of WNP TCCs in May. In October, stronger SST warming in the tropical Atlantic and Indian Oceans contributed to anomalous easterlies over the tropical WNP associated with anomalous anticyclonic circulation, giving rise to the suppressed atmospheric eddy kinetic energy and recent weakened GP of WNP TCCs. These results highlight the seasonality in recent changing tendencies in the GP of WNP TCCs and associated large-scale atmospheric-oceanic conditions.

Fungal symbioses with plants are ubiquitous, ancient, and vital to both ecosystem function and plant health. However, benefits to fungal symbionts are not well explored, especially in non‐mycorrhizal fungi. The Foraging Ascomycete hypothesis proposes that some wood‐decomposing fungi may shift life‐history strategies to endophytism to bridge gaps in time and space between suitable substrates. To test this hypothesis we examine spatial relationships of Xylaria endophytic fungi in the forest canopy with Xylaria decomposer fungi on the forest floor. We sampled for fungi of the genus Xylaria using a spatially explicit sampling scheme in a remote Ecuadorian cloud forest, and concurrently carried out an extensive culture‐based sampling of fungal foliar endophytes. We found 36 species of Xylaria in our 0.5 ha plot, 31 of which were found to only occur as fruiting bodies. All five species of Xylaria found as endophytes were also found as fruiting bodies. We also tested the relationships of both stages of these fungi to environmental variables. Decomposer fungi were differentiated by species‐specific habitat preferences, with three species being found closer to water than expected by chance. In contrast, endophytes displayed no sensitivity to environmental conditions, such as host, moisture, or canopy cover. We found evidence of spatial linkage between life stages in two species. We also demonstrate that direct transmission of endophytes from leaves to woody substrates is possible. These results indicate that endophytism may represent one way for decomposer fungi to escape moisture limitation, and that endophytic fungi may act as sources of dispersal for decomposer fungi consistent with predictions of the Foraging Ascomycete hypothesis.