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The physical behavior of a falling raindrop is governed by delicate fluid dynamics and thermodynamics, and oscillates with time. Despite this time‐variant nature, past observational and simulation studies have aimed to generalize parameterizations for describing rain microphysics bearing the assumption that raindrops fall at terminal speeds with an equilibrium shape. However, the applicability of this hypothesis in a realistic atmosphere that is inherently turbulent remains an open question. Here, we employ novel retrieval techniques to quantify the impact of turbulence on raindrop microphysics using long‐term in situ observations with careful assessment of the wind effect. We find that raindrop microphysics increasingly deviate from the equilibrium state as the turbulence dissipation rate increases, and this effect is more pronounced for large raindrops. We present turbulence‐invoked rain microphysical parameterizations which shed light on the complex interactions between turbulence dynamics and raindrop microphysics. Plain Language Summary: Raindrops are omnipresent in the atmosphere and play an essential role in the global hydrological cycle. The microphysics of raindrops, namely, shape, orientation and fall speed, have long been represented as a function of diameter with an equilibrium state. This simplification omits the impact of ubiquitous turbulence in the atmosphere. This study quantifies the deformation of raindrops under turbulent conditions. We find that the shape of large raindrops is more rounded and that raindrop oscillation is more pronounced in response to strong turbulence. Their fall speeds are significantly lower than the terminal speed, and the corresponding standard deviations are greater. Our work demonstrates the necessity of physically representing turbulence dynamics for accurate parameterization of raindrop microphysics via numerical simulations. Key Points: Raindrop microphysics increasingly deviate from the equilibrium state as the turbulence dissipation rate increasesLarge raindrops exhibit rounder shapes and lower fall speeds under strong turbulenceTurbulence‐invoked raindrop microphysics parameterizations are given [ABSTRACT FROM AUTHOR]

Abstract The physical behavior of a falling raindrop is governed by delicate fluid dynamics and thermodynamics, and oscillates with time. Despite this time‐variant nature, past observational and simulation studies have aimed to generalize parameterizations for describing rain microphysics bearing the assumption that raindrops fall at terminal speeds with an equilibrium shape. However, the applicability of this hypothesis in a realistic atmosphere that is inherently turbulent remains an open question. Here, we employ novel retrieval techniques to quantify the impact of turbulence on raindrop microphysics using long‐term in situ observations with careful assessment of the wind effect. We find that raindrop microphysics increasingly deviate from the equilibrium state as the turbulence dissipation rate increases, and this effect is more pronounced for large raindrops. We present turbulence‐invoked rain microphysical parameterizations which shed light on the complex interactions between turbulence dynamics and raindrop microphysics.

• Three instruments were compared in the lab under simulated rainfall conditions. • The raindrop size was most accurately described using the geometric mean diameter. • The raindrop visual measurement method could provide accurate raindrop shapes. • The laser precipitation monitor was more sensitive to measuring raindrops of < 1 mm. • Based on rainfall tests, the applicability of the three instruments was discussed. Precipitation microphysics, which describes the basic characteristics of rainfall, is important for agricultural praxis, weather prediction, aviation safety, and soil erosion prediction. In this study, three types of instruments (a laser precipitation monitor, LPM; piezoelectric transducer, PT; and particle imaging transient visual measurement technology, PIV) were employed to measure and compare the raindrop size distribution (DSD) and rainfall kinetic energy rate (KE t) under simulated rainfall conditions. Comparisons of the results indicated that under the same simulated rainfall conditions, the number of raindrops per unit area measured by LPM was larger than that measured by PIV. The DSD measured by PIV was more uniform than that of the PT and LPM under the same rainfall conditions. The raindrop size range measured by the LPM was smaller than that measured by the PT and PIV. In addition, the geometric mean diameter was a more accurate representation of raindrop size because PIV can capture the true irregular shape of raindrops. Compared to the PIV sensor, the LPM underestimates the raindrop diameter. The median raindrop diameter measured and calculated by PIV using the geometric mean diameter was approximately 1.61 times that of LPM. The KE t values measured by PIV and PT were approximately similar, while the KE t calculated by LPM was 0.51 and 0.57 times that of PIV and PT for the same rainfall conditions, respectively. A correction factor of 1.75 provided an approximate reference for the calibration of the kinetic energy calculation of the LPM instrument. The above results can provide basic insights for calibration and application of the three instruments. [ABSTRACT FROM AUTHOR]