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Abstract Supercooled liquid clouds are ubiquitous over the Southern Ocean (SO), even to temperatures below −20°C, and comprise a large fraction of the marine boundary layer (MBL) clouds. Earth system models and reanalysis products have struggled to reproduce the observed cloud phase distribution and occurrence of cloud ice in the region. Recent simulations found the microphysical representation of ice nucleation and growth has a large impact on these properties, however, measurements of SO ice nucleating particles (INPs) to validate simulations are sparse. This study presents measurements of INPs from simultaneous aircraft and ship campaigns conducted over the SO in austral summer 2018, which include the first in situ observations in and above cloud in the region. Our results confirm recent observations that INP concentrations are uniformly lower than measurements made in the late 1960s. While INP concentrations below and above cloud are similar, higher ice nucleation efficiency above cloud supports model simulations that the dominant INP composition varies with height. Model parameterizations based solely on aerosol properties capture the mean relationship between INP concentration and temperature but not the observed variability, which is likely related to the only modest correlations observed between INPs and environmental or aerosol metrics. Including wind speed in addition to activation temperature in a marine INP parameterization reduces bias but does not explain the large range of observed INP concentrations. Direct and indirect inference of marine INP size suggests MBL INPs, at least during Austral summer, are dominated by particles with diameters smaller than 500 nm.
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Radar First Echo Detection With Spaceborne Precipitation Radars
Abstract The radar “first echo” appears in a fresh growing cloud when hydrometeors grow to large enough sizes to be detected by radar. Using 26‐year observations by the Ku band radars onboard the Global Precipitation Mission and the Tropical Rainfall Measurement Mission satellites, isolated pixels with detectable radar echoes at altitude and without precipitation at the surface are identified as candidate “first echoes.” In general, the appearance of the “first echoes” show three altitude‐related modes in the tropics. The shallow mode at 1.5–2 km is mainly from the growth of warm rain from rapid coalescence. The mid mode between 0°C and −7°C is found mainly over land and coastal regions, that can be explained by the enhanced radar reflectivity by ice particles through heterogenous ice nucleation at relative warmer temperatures, followed by active riming. The deep mode between −12°C and −25°C is frequently found over both land and ocean. Around 12% of isolated echoes, mainly over desert regions, could be the remnant of dissipating precipitation, like virga. Cloud base height and total column water vapor derived from ERA5 reanalysis are found positively related to the “first echo” height. The mid mode first echoes are more likely found in a moist (ice‐supersaturated) environment, a favorable condition for crystal growth following heterogeneous ice nucleation. While the shallow mode over ocean tends to have more sea salt aerosols, large smoke and sulfate aerosol concentrations are often associated with the mid mode, and large dust aerosol concentrations are often involved with the deep mode.
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- Award ID(s):
- 1945871
- PAR ID:
- 10671434
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Atmospheres
- Volume:
- 130
- Issue:
- 24
- ISSN:
- 2169-897X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1029/2025JD045191
