 |
| Titel |
Characteristic nature of vertical motions observed in Arctic mixed-phase stratocumulus |
| VerfasserIn |
J. Sedlar, M. D. Shupe |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1680-7316
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 14, no. 7 ; Nr. 14, no. 7 (2014-04-07), S.3461-3478 |
| Datensatznummer |
250118568
|
| Publikation (Nr.) |
 copernicus.org/acp-14-3461-2014.pdf |
|
|
|
|
|
| Zusammenfassung |
Over the Arctic Ocean, little is known on cloud-generated buoyant
overturning vertical motions within mixed-phase stratocumulus clouds.
Characteristics of such motions are important for understanding the diabatic
processes associated with the vertical motions, the lifetime of the cloud
layer and its micro- and macrophysical characteristics.
In this study, we exploit a suite of surface-based remote sensors over the
high-Arctic sea ice during a weeklong period of persistent stratocumulus in
August 2008 to derive the in-cloud vertical motion characteristics. In-cloud
vertical velocity skewness and variance profiles are found to be strikingly
different from observations within lower-latitude stratocumulus, suggesting
these Arctic mixed-phase clouds interact differently with the atmospheric
thermodynamics (cloud tops extending above a stable temperature inversion
base) and with a different coupling state between surface and cloud. We find
evidence of cloud-generated vertical mixing below cloud base, regardless of
surface–cloud coupling state, although a decoupled surface–cloud state
occurred most frequently. Detailed case studies are examined, focusing on
three levels within the cloud layer, where wavelet and power spectral analyses are
applied to characterize the dominant temporal and horizontal scales
associated with cloud-generated vertical motions. In general, we find a
positively correlated vertical motion signal amongst vertical levels within
the cloud and across the full cloud layer depth. The coherency is dependent
upon other non-cloud controlled factors, such as larger, mesoscale weather
passages and radiative shielding of low-level stratocumulus by one or more
cloud layers above. Despite the coherency in vertical velocity across the
cloud, the velocity variances were always weaker near cloud top, relative to
cloud middle and base. Taken in combination with the skewness, variance and
thermodynamic profile characteristics, we observe vertical motions near
cloud top that behave differently than those from lower within the cloud
layer. Spectral analysis indicates peak cloud-generated w variance
timescales slowed only modestly during decoupled cases relative to coupled;
horizontal wavelengths only slightly increased when transitioning from
coupling to decoupling. The similarities in scales suggests that perhaps the
dominant forcing for all cases is generated from the cloud layer, and it is
not the surface forcing that characterizes the time- and space scales of
in-cloud vertical velocity variance. This points toward the resilient nature
of Arctic mixed-phase clouds to persist when characterized by thermodynamic
regimes unique to the Arctic. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|