Numerous observational and modeling studies have addressed the impact of soil moisture on subsequent precipitation (primarily its initiation), yet consensus remains elusive. Here we quantify the relationship between soil moisture and precipitation amplification over the U.S. Southern Great Plains. Warm season (June–September) days for the 2002–2011 period (with ~1220 total days) are partitioned into three dynamic regimes based on daily water vapor convergence, among which afternoon precipitation event days are identified based on simple criteria. We find that antecedent soil moisture conditions are negatively correlated with subsequent afternoon precipitation magnitude for low dynamic regimes, but this correlation becomes positive for high dynamic regimes. In contrast, this correlation is markedly reduced in magnitude and becomes insignificant when all regime days are considered. These results are also confirmed by analyzing the precipitation histogram and diurnal cycle. Furthermore, different pathways are provided for precipitation amplification for low and high dynamic regimes.
In this study, we analyze the relationships between summer afternoon low cloud cover and environmental conditions over the Tibetan Plateau (TP). Using in situ measurements, satellite data, and reanalysis, and based on theoretical analysis, we find that there is stronger thermal turbulence, lower temperature, and higher frequency of low cloud formation for the same surface relative humidity over the eastern and central TP compared with eastern China. With the same sensible heat flux, decreased air density enhances buoyancy flux, which increases the planetary boundary layer height and moisture vertical transport. At the same time, with the same near-surface relative humidity, lower temperature over the TP decreases the lifting condensation level, which increases the probability of the air parcel reaching this level. Compared to the low-elevation region in eastern China, these two mechanisms enhance low cloud occurrence in the afternoon over the TP. Plain Language Summary Previous studies suggested that planetary boundary layer processes play an important role in the formation of more low clouds in the afternoon over the Tibetan Plateau (TP). However, detailed mechanisms for the differences in low cloud occurrence in the afternoon over the TP versus eastern China (low-elevation region) remain unclear. Using in situ measurements, satellite data, and reanalysis, and based on theoretical analysis, we first quantify the more frequent low cloud occurrence over the TP, and then propose two mechanisms: (i) compared to eastern China, in the afternoon over the TP, the lower near-surface temperature results in a lower height where condensation occurs (given the same relative humidity), and (ii) the lower air density (given the same surface sensible heat flux) results in a larger buoyancy flux, leading to a deeper boundary layer. These two mechanisms work together to increase cloud formation in the afternoon over the TP.
The relationship between morning soil moisture and afternoon rainfall persists as an important yet unresolved challenge in land‐atmosphere interaction study, complicated in part by atmospheric influence. Here, we address this relationship by utilizing NASA's satellite soil moisture and precipitation data for the warm season (June–September) of 2015–2019 over Northern Hemisphere land (0–60°N). Raining days are partitioned into low, medium, and high regimes of atmospheric water vapor convergence. Under the low convergence regime, afternoon rainfall is more likely to occur over wetter soils or higher relative humidity; for days with high moisture convergence, occurrence favors drier soils or lower relative humidity. For each regime, afternoon rainfall occurrence favors warmer morning soil or air temperature. These conclusions are not affected by the threshold magnitude utilized to identify afternoon rainfall events by accumulation, but the threshold value does affect the soil moisture (or relative humidity)‐precipitation relationship when convergence regimes are not considered.
Snowmelt is an essential process for the health and sustenance of numerous communities and ecosystems across the globe, though it also presents potential hazards when ablation processes are exceedingly rapid. Using 4 km daily snow water equivalent, temperature, and precipitation data for three decades (1988-2017), here we provide a broad characterization of extreme snowmelt episodes over the conterminous U.S. in terms of magnitude, timing, and coincident synoptic weather patterns. Larger magnitude extreme snowmelt events usually coincide with minimal precipitation and elevated temperatures. However, certain regions, particularly mountainous regions and the northeast U.S., exhibit greater likelihood of extreme snowmelt events during pronounced rain-on-snow events. During snowmelt extremes, snowmelt rate often exceeds precipitation in many regions. Meteorological patterns and associated water vapor transport most directly connected to extreme events over different regions are classified via a machine learning technique. Over the 30-year study period, there is a weakly increasing trend in the frequency of extremes, though this does not necessarily signify an increase in snowmelt magnitudes.
Snow is an important part of wintertime in mid-to high latitudes, as it fundamentally changes the land surface. It changes the surface energy balance by increasing surface albedo (Betts et al., 2014;Flanner et al., 2011;Hall, 2004), causing a positive snow albedo feedback. This feedback leads to an enhancement of climate variations and trends in snow-covered regions, making it a leading factor in the amplification of global warming in the northern high-latitudes (
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