Cloud Adiabaticity and Its Relationship to Marine Stratocumulus Characteristics Over the Northeast Pacific Ocean

Abstract

Cloud adiabaticity (α) is defined as the ratio of the actual liquid water path (LWPmeasured) in a cloud to its corresponding adiabatic value (LWPad). Processes such as drizzle and entrainment can lead to subadiabatic LWPmeasured. This study examines α and its relationship to microphysical properties for 86 cloud events over the Northeast Pacific Ocean based on data collected during four separate summertime airborne campaigns. For the study region, α was found to be 0.766 ± 0.134. For most cases, clouds with a low value of α were found to have lower droplet number concentration (Nd), higher droplet effective radius (re), higher relative dispersion (d), and higher rain rate (R). The subcloud aerosol concentration (Na) was often less for the low‐α cases. The relationship between α and the vertical profiles and cloud‐top characteristics for both the cloud droplet‐only spectrum and full spectrum (cloud and rain droplets) is also examined. Inclusion of rain droplets produced a larger change in d for the low‐α clouds as compared to the high‐α clouds. On average, R increased at cloud top for high‐α clouds but decreased at cloud top for low‐α clouds. Accounting for α when estimating Nd from Moderate Resolution Imaging Spectroradiometer retrievals results in better agreement with in situ Nd values. Results of this work motivate the need for additional focus on the factors governing α, such as cloud type, and implications of its value, especially for remote‐sensing retrievals.

Stratocumulus cloud clearings: statistics from satellites, reanalysis models, and airborne measurements

“…Consistent with previous studies (Neiburger et al, 1961;Wood and Bretherton, 2004), regardless of whether clearings were present, PBLH generally increases with distance from the coast (Fig. 8d), where warmer SSTs lead to a deeper MBL by weakening the inversion (Bretherton and Wyant, 1997). The shallowing of the MBL near the coast of California is also notable with enhanced gradients on clearing days.…”

“…It is important to note that the adiabaticity parameter, defined as the ratio of measured LWP to LWP of an adiabatic cloud, exhibited values of 0.75, 0.76, and 0.83 for RF08, RF09A, and RF09B, respectively. These adiabaticity values are close to the average value of 0.766 for the region reported in Braun et al (2018). The clouds were quite thin near the interface based on the relatively low values of LWP in contrast to typical conditions observed in the region based on airborne measurements in the same campaigns ( Fig.…”

Deconvolution of boundary layer depth and aerosol constraints on cloud water path in subtropical stratocumulus decks

“…Adiabaticity is known to change with cloud depth in marine stratocumulus (Merk et al, 2016;Braun et al, 2018). Furthermore, we find that clouds in deep BLs are more likely to precipitate than clouds in shallow BLs (Fig.…”

“…Future analyses of past campaigns summarised in Zuidema et al (2016) will likely increase the data points sampled in deeper BLs. References: Jiang et al (2002), Johnson et al (2004), Lu and Seinfeld (2005), Bretherton et al (2007), Sandu et al (2008), , , Yi et al (2008), Xue et al (2008), Caldwell and Bretherton (2009), Ackerman et al (2009), Sandu et al (2009), Hill and Feingold (2009) 2018, Augstein et al (1973), Lenschow et al (1988), Albrecht et al (1988Albrecht et al ( , 1995, Stevens et al (2003), Bretherton et al (2004), Lu et al (2007Lu et al ( , 2009, and Wood et al (2011).…”

Aerosol–Cloud–Meteorology Interaction Airborne Field Investigations: Using Lessons Learned from the U.S. West Coast in the Design of ACTIVATE off the U.S. East Coast

“…The boundary layer height for the coastal California clouds can be extremely shallow (Zuidema et al 2009), with cloud-top heights (CTHs) ranging in these f lights between 135 and 1,150 m, with a mean of 541 m. Cloud depths and liquid water paths (LWPs) ranged between 40 and 760 m and 10 and 310 g m -2 , respectively. Clouds were typically subadiabatic (average adiabaticity = 0.766 ± 0.134; Braun et al 2018). On average, the observed LWC lapse rate tended to be a fairly constant fraction of the adiabatic LWC lapse rate through the bottom 90% by height of the cloud; however, in the top 10% of the cloud, a sharp decrease in LWC was observed [Fig.…”