Lagrangian Cloud Tracking and the Precipitation-Column Humidity Relationship

Abstract

Abstract:The tropical, oceanic mean relationship between column relative humidity and precipitation is highly non-linear. Mean precipitation remains weak until it rapidly picks up and grows at high column humidity. To investigate the origin of this relationship, a Lagrangian cloud tracking code, RAMStracks, is developed, which can follow the evolution of clouds. RAMStracks can record the morphological properties of convective clouds, the meteorological environment of clouds, and their effects. RAMStracks is applied to a large-domain radiative convective equilibrium simulation, which produces a complex population of convective clouds. RAMStracks records the lifecycle of 501 clouds through growth, splits, mergers, and decay. The mean evolution of all these clouds is examined. It is shown that the column humidity evolves non-monotonically, but that lower-level and upper-level contributions to total moisture do evolve monotonically. The precipitation efficiency of tropical storms tends to increase with cloud age. This is confirmed using a prototype testing method. The same method reveals that different tracked clouds with similar initial conditions evolve in very different ways. This makes drawing general conclusions from individual storms difficult. Finally, the causality of the precipitation-column humidity relationship is examined. A Granger Causality test, as well as regressions, suggest that moisture and precipitation are causally linked, but that the direction of causality is ambiguous. Much of this link appears to come from the lower-level moisture's contribution to column humidity.

Environmental Controls on Tropical Mesoscale Convective System Precipitation Intensity

“…In addition to considering the areal coverage of convection, the near-linear relationship between total system radius, convective core radius, and P max may also result from the fact that the convective cores within larger systems may be more protected from dilution due to dry air entrainment than in smaller systems. This would be consistent with literature surrounding decreased entrainment with increasing radii of convective plumes (e.g., Simpson 1971;de Rooy et al 2013;Hannah 2017;Igel 2018), whereby precipitation production may be more efficient given the same CWV relative to MCSs with FIG. 9.…”

Factors Affecting Entrainment Rate in Deep Convective Clouds and Parameterizations

“…Convective clouds are important in shaping Earth's climate and weather; they affect the hydrological and energy cycles through the transport of heat, moisture, and momentum (de Rooy et al., 2013; Igel, 2018; Li & Zhang, 2017; Xue et al., 2008; Yang et al., 2017; Zhang et al., 2018a, 2018b; Zheng & Rosenfeld, 2015). The entrainment‐mixing process between clouds and their environments is one of the most sensitive and uncertain processes in cumulus convection (Lu & Ren, 2016; Luo et al., 2010; Wang, 2020; Yang et al., 2013).…”

Upper‐Tropospheric Troughs and North American Monsoon Rainfall in a Long‐Term Track Dataset

“…Given the episodic nature of precipitation, it's possible that our composite view misses some interesting TUTT behavior. Employing evolutionary prototype methods (e.g., Igel, 2018) might help to categorize and identify frequent development patterns of precipitation throughout the lifetime of TUTTs that are difficult to recognize from composites.…”