Convective Wakes in the Equatorial Western Pacific during TOGA

Young, George S.; Perugini, Samuel M.; Fairall, C. W.

doi:10.1175/1520-0493(1995)123<0110:cwitew>2.0.co;2

Cited by 88 publications

(70 citation statements)

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“…Moreover, the analysis of mean precipitation in convective areas has shown that aggregated convection is statistically characterized by more intense rainfall events at the mesoscale than scattered convection (not shown), which is also in agreement with Bretherton et al (2005). The results related to surface turbulent fluxes are also consistent with previous observational studies (Saxen and Rutledge 1998;Jabouille et al 1996;Young et al 1995).…”

Section: ) Physical Mechanismssupporting

confidence: 89%

“…This effect could imply a modulation of mean surface fluxes at larger scales [Jabouille et al (1996) show it at a smaller scale than in the present study]. Cold pools formed under convective systems, whose characteristics are likely to be affected by convective organization, may play a role in the modulation of surface fluxes intensity, through the generation of gust winds and air-sea differences (Young et al 1995).…”

Section: ) Physical Mechanismsmentioning

confidence: 53%

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Observational Evidence for Relationships between the Degree of Aggregation of Deep Convection, Water Vapor, Surface Fluxes, and Radiation

2012

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Tropical deep convection exhibits complex organization over a wide range of scales. This study investigates the relationships between the spatial organization of deep convection and the large-scale atmospheric state. By using several satellite datasets and reanalyses, and by defining a simple diagnostic of convective aggregation, relationships between the degree of convective aggregation and the amount of water vapor, turbulent surface fluxes, and radiation are highlighted above tropical oceans. When deep convection is more aggregated, the middle and upper troposphere are drier in the convection-free environment, turbulent surface fluxes are enhanced, and the low-level and midlevel cloudiness is reduced in the environment. Humidity and cloudiness changes lead to a large increase in outgoing longwave radiation. Cloud changes also result in reduced reflected shortwave radiation. Owing to these opposing effects, the sensitivity of the radiative budget at the top of the atmosphere to convective aggregation turns out to be weak, but the distribution of radiative heating throughout the troposphere is affected. These results suggest that feedbacks between convective aggregation and the large-scale atmospheric state might influence large-scale dynamics and the transports of water and energy and, thus, play a role in the climate variability and change. These observational findings are qualitatively consistent with previous cloud-resolving model results, except for the effects on cloudiness and reflected shortwave radiation. The proposed methodology may be useful for assessing the representation of convective aggregation and its interaction with the large-scale atmospheric state in various numerical models.

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Section: ) Physical Mechanismssupporting

confidence: 89%

Section: ) Physical Mechanismsmentioning

confidence: 53%

Observational Evidence for Relationships between the Degree of Aggregation of Deep Convection, Water Vapor, Surface Fluxes, and Radiation

2012

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“…This implies that the interactions between cold pools and surface fluxes cannot be represented. This effect has so far mostly been shown to be important for oceanic convection (e.g., Johnson and Nicholls 1983;Young et al 1995;Ross et al 2004), whereas our study focuses on continental convection. Nevertheless, to investigate the effect of prescribed surface fluxes on the results, one simulation has been repeated using an interactive land surface model.…”

Section: A Model Description and Experimental Setupmentioning

confidence: 99%

“…An aggregation of moisture around the edges of the cold pools and the subsequent preferred cloud development on these moist spots has been witnessed in simulations of organized shallow convection (Seifert and Heus 2013). In their composite analysis of observed cold pools, Young et al (1995) noted, moreover, a depression in the surface air temperature of 2-3 K that was followed by a decrease of the mixing ratio of 0.3-1 g kg 21 . The ability of density currents to transport moisture from the wet monsoon areas into the very dry Sahara, where subsequent cloud development occurs, has in addition been documented in Flamant et al (2009).…”

Section: Introductionmentioning

confidence: 99%

“…Observational evidence of cold-pool-generated convective cells is available for shallow maritime convection (Warner et al 1979;Zuidema et al 2012), maritime deep convection (Barnes and Garstang 1982;Addis et al 1984;Young et al 1995), and continental deep convection (e.g., Lima and Wilson 2008;Lothon et al 2011;Dione et al 2013). There is moreover a large amount of literature on the role of cold pools in the organization of multicell convection such as squall lines (e.g., Wakimoto 1982) or mesoscale convective systems (e.g., Fritsch and Forbes 2001;Engerer et al 2008).…”

Section: Introductionmentioning

confidence: 99%

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The Formation of Wider and Deeper Clouds as a Result of Cold-Pool Dynamics

Schlemmer

Hohenegger

2014

Journal of the Atmospheric Sciences

145

192

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This study investigates how precipitation-driven cold pools aid the formation of wider clouds that are essential for a transition from shallow to deep convection. In connection with a temperature depression and a depletion of moisture inside developing cold pools, an accumulation of moisture in moist patches around the cold pools is observed. Convective clouds are formed on top of these moist patches. Larger moist patches form with time supporting more and larger clouds. Moreover, enhanced vertical lifting along the leading edges of the gravity current triggered by the cold pool is found. The interplay of moisture aggregation and lifting eventually promotes the formation of wider clouds that are less affected by entrainment and become deeper. These mechanisms are corroborated in a series of cloud-resolving model simulations representing different atmospheric environments. A positive feedback is observed in that, in an atmosphere in which cloud and rain formation is facilitated, stronger downdrafts will form. These stronger downdrafts lead to a stronger modification of the moisture field, which in turn favors further cloud development. This effect is not only observed in the transition phase but also active in prolonging the peak time of precipitation in the later stages of the diurnal cycle. These findings are used to propose a simple way for incorporating the effect of cold pools on cloud sizes and thereby entrainment rate into parameterization schemes for convection. Comparison of this parameterization to the cloud-resolving modeling output gives promising results.

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Variability in surface meteorology and air‐sea fluxes due to cumulus convective systems observed during CINDY/DYNAMO

2014

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This study examines the variability in surface meteorological parameters and air-sea heat fluxes due to cold pools emanating from cumulus convective systems observed over the tropical Indian Ocean in November 2011. In particular, this study focuses on convective systems that are spatially smaller than mesoscale convective systems in a southeasterly trade wind environment. Composite analyses of convectively active periods show an increase in the sensible heat flux by 15-20 W m À2 that is primarily attributed to an increase in the difference between the surface air temperature and sea surface temperature and an increase in the latent heat flux by 30-70 W m À2 due to enhanced surface wind speeds. A succession of convectively active periods leads to a greater influence than those occurring independently. The direction of the surface wind velocity anomaly due to cold pools tends to be close to that of the environmental wind velocity, resulting in an efficient enhancement of wind speed. This study also demonstrates the close relation between cold pool intensities and convective activity. In particular, two measures of cold pool intensity, a minimum surface air temperature and a maximum amount of surface wind speed enhancement, are correlated with each other and with the convective activity around the observation point measured by radar-estimated rainfall and radar echo coverage.

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Convective Wakes in the Equatorial Western Pacific during TOGA

Cited by 88 publications

References 0 publications

Observational Evidence for Relationships between the Degree of Aggregation of Deep Convection, Water Vapor, Surface Fluxes, and Radiation

Observational Evidence for Relationships between the Degree of Aggregation of Deep Convection, Water Vapor, Surface Fluxes, and Radiation

The Formation of Wider and Deeper Clouds as a Result of Cold-Pool Dynamics

Variability in surface meteorology and air‐sea fluxes due to cumulus convective systems observed during CINDY/DYNAMO

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