Surface-based observations of cold-air outbreak clouds during the COMBLE field campaign

Abstract

Abstract. Cold-air outbreaks (CAOs) are characterized by extreme air–sea energy exchanges and low-level convective clouds over large areas in the high-latitude oceans. As such, CAOs are an important component of the Earth's climate system. The CAOs in the Marine Boundary Layer Experiment (COMBLE) deployment of the US Department of Energy Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF) provided the first comprehensive view of CAOs using a suite of ground-based observations at the northern coast of Norway. Here, cloud and precipitation observations from 13 CAO cases during COMBLE are analyzed. A vertical air motion retrieval technique is applied to the Ka-band ARM Zenith-pointing Radar (KAZR) observations. The CAO cumulus clouds are characterized by strong updrafts with magnitudes between 2–8 m s−1, vertical extents of 1–3 km, and horizontal scales of 0.25–3 km. A strong relationship between our vertical air velocity retrievals and liquid water path (LWP) measurements is found. The LWP measurements exceed 1 kg m−2 in strong updraft areas, and the vertical extent of the updraft correlates well with the LWP values. The CAO cumulus clouds exhibit eddy dissipation rate values between 10−3 and 10−2 m2 s−3 in the lowest 10 km of the atmosphere, and using a radar Doppler spectra technique, evidence of secondary ice production is found during one of the cases.

Air mass history linked to the development of Arctic mixed-phase clouds

“…In contrast, the liquid phase is persistently dominant in non-MCAO clouds, with particularly few ice-only clouds. The shift towards a more glaciated state in MCAO clouds is in agreement with previous in-situ and measurement campaign observations (Abel et al, 2017;Lloyd et al, 2018;Mages et al, 2023), with higher amounts of ice found in the post-transition cumuliform clouds than in the original stratiform decks.…”

“…Secondary ice production has previously been cited as a cause of mixed-phase development in MCAO; during a field campaign, Abel et al (2017) found that the number of ice crystals in the post-transition cumuliform clouds was several order of magnitudes greater than what would be expected given the ambient INP concentrations. Mages et al (2023) also found evidence of secondary ice production in the later stages of an outbreak. In both cases, cloud temperatures were within that of the Hallett-Mossop mechanism and strong updrafts were recorded.…”

“…Schirmacher et al (2023) found that CloudSat may also underestimate precipitation, particularly frozen precipitation, in outbreaks due to limitations such as surface clutter creating a blind zone for the radar close to the surface. While the COMBLES campaign took in-situ precipitation measurements during outbreaks, and found that the cumuliform clouds were typically precipitating (Mages et al, 2023), with frozen precipitation being common, there is still a great deal of uncertainty about the phase of the precipitation created in these events. Therefore, it is difficult to assess how prevalent retrieval errors may be.…”

Using Satellite and ARM Observations to Evaluate Cold Air Outbreak Cloud Transitions in E3SM Global Storm‐Resolving Simulations

“…Although grid‐boxes with high cloud liquid water fraction mainly locate around cloud edges in cloud streets and cumulus regimes (Figure 3a), a very small portion (≤0.01 Joint‐PDF value) of high IWPs (≥200 g/m 2 ) in the cumulus cloud regime is found in downdrafts (Figure 4g), likely around the edges of deeper cumulus clouds (Figures 3a, 3b, and 3e). Previous observational studies using ground‐based data found strong correlations between vertical velocity and both IWP and LWP in Arctic mixed‐phase stratiform clouds (Shupe et al., 2008) and between the cloud liquid water and updrafts in COMBLE MCAO cumulus clouds (Mages et al., 2023). Air‐borne flight data indicate no evidence of cloud ice collocating with strong updrafts in the Southern Ocean cumulus clouds (Hu, Geerts, et al., 2023).…”

Vertical Structure of Clouds and Precipitation During Arctic Cold‐Air Outbreaks and Warm‐Air Intrusions: Observations From COMBLE

“…Surface precipitation type was difficult to identify with the AMF1 measurements (Mages et al, 2023). The 2-m temperature remained below freezing during this CAO.…”