The PHAse Cloud Type (PHACT) product

Description

The PHAse Cloud Type (PHACT) product development has been guided by recent ground-based observations to document the topmost liquid-bearing cloud layers for different cloud types (ice over liquid, liquid only, liquid seeded by ice above, mixed-phase, multilayer and single layer etc.) and for thin (optical depth < 3) and opaque (optical depth > 3) clouds. PHACT uses instantaneous CALIPSO-GOCCP cloud profiles (Cesana et al., 2013; Chepfer et al., 2010) at a 333 m along-track resolution and for 480 m altitude bins. Liquid- and ice-dominated cloudy bins are discriminated using the polarization state of the CALIPSO lidar return, different for non-spherical crystals and spherical droplets.  

PHACT documents ice-only (no liquid in the column), mixed-phase (liquid with ice below, contiguous or not) and liquid (with possibly ice above) cloud covers. Additionally, the phase cloud cover is computed as the number of cloud phase type profiles divided by the total number of profiles, consistent with the common definition of cloud cover:

CCphase = Nphase / NprofilesWhere phase means either ice, liquid or mixed-phase.

Therefore, the sum of all cloud covers cannot be greater than 1. PHACT contains a mixed-phase category, which is not available in CALIPSO-GOCCP. Mixed-phase clouds are defined as liquid clouds with ice or undefined-phase clouds underneath, directly or not. Undefined-phase clouds are defined as cloudy bins that are located below highly reflective cloud bins. At subfreezing temperatures, undefined-phase clouds are typically mixed-phase clouds(Cesana et al. 2016).BAsed on a validation study against in situ aircraft measurements, the maximum disagreement fraction between CALIPSO-GOCCP instantaneous profiles, which are used to create PHACT statistics, and five in situ aircraft flights is 11.8% when accounting for in situ aircraft measurement uncertainty (Cesana et al. 2016; their Table 3). 

PHACT2D_200701-202012_avg_2.5x2.5_3.1.2_v1.52.nc: This file contains the monthly mean 2D cloud covers for the different cloud phase types (all documented in the file), over a 2.5˚x2.5˚ grid for the 2007-2020 period.

PHACT3D_200701-202012_avg_2.5x2.5_3.1.2_v1.52.nc: This file contains the monthly mean 3D cloud fractions for the different cloud phase types (all documented in the file), over a 2.5˚x2.5˚ horizontal grid and for 480m altitude bins from 0 to 19.2 km, for the 2007-2020 period.

References

Cesana, G.V., O. Pierpaoli, M. Ottaviani, L. Vu, Z. Jin and I. Silber, 2024: The correlation between Arctic sea ice, cloud phase and radiation using A-train satellites. Atmos. Chem. Phys., accepted.

Cesana, G., H. Chepfer, D. Winker, B. Getzewich, X. Cai, O. Jourdan, G. Mioche, H. Okamoto, Y. Hagihara, V. Noel, and M. Reverdy, 2016: Using in situ airborne measurements to evaluate three cloud phase products derived from CALIPSO. J. Geophys. Res. Atmos., 121, no. 10, 5788-5808, doi:10.1002/2015JD024334.

Cesana, G., and H. Chepfer, 2013: Evaluation of the cloud thermodynamic phase in a climate model using CALIPSO-GOCCP. J. Geophys. Res. Atmos., 118, no. 14, 7922-7937, doi:10.1002/jgrd.50376.

Chepfer, H., S. Bony, D. Winker, G. Cesana, J.L. Dufresne, P. Minnis, C.J. Stubenrauch, and S. Zeng, 2010: The GCM-Oriented CALIPSO Cloud Product (CALIPSO-GOCCP). J. Geophys. Res., 115, no. D4, D00H16, doi:10.1029/2009JD012251.