Cumulus dynamics: Local compensating subsidence and its implications for cumulus parameterization

Fritsch, J. Michael

doi:10.1007/bf01592963

Cited by 24 publications

(11 citation statements)

References 27 publications

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“…These middle-and upper-level downdrafts are documented in previous studies of MCSs, which suggest that they form in response to the pressure field (e.g., Biggerstaff and Houze, 1991), can occur quite close to the updraft (Lily, 1960;Fritsch, 1975), and are positively buoyant (Fovell and Ogura, 1988; Jorgensen and LeMone, 1989;Sun et al, 1993). These motions produce gravity waves in the stratosphere, as is discussed in Fovell et al (1992).…”

Section: Downdraft Origin and The Effects Of Mixingmentioning

confidence: 56%

Tropical continental downdraft characteristics: mesoscale systems versus unorganized convection

Schiro

Neelin

2018

Atmos. Chem. Phys.

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Abstract. Downdrafts and cold pool characteristics for strong mesoscale convective systems (MCSs) and isolated, unorganized deep precipitating convection are analyzed using multi-instrument data from the DOE Atmospheric Radiation Measurement (ARM) GoAmazon2014/5 campaign. Increases in column water vapor (CWV) are observed leading convection, with higher CWV preceding MCSs than for isolated cells. For both MCSs and isolated cells, increases in wind speed, decreases in surface moisture and temperature, and increases in relative humidity occur coincidentally with system passages. Composites of vertical velocity data and radar reflectivity from a radar wind profiler show that the downdrafts associated with the sharpest decreases in surface equivalent potential temperature (θ e ) have a probability of occurrence that increases with decreasing height below the freezing level. Both MCSs and unorganized convection show similar mean downdraft magnitudes and probabilities with height. Mixing computations suggest that, on average, air originating at heights greater than 3 km must undergo substantial mixing, particularly in the case of isolated cells, to match the observed cold pool θ e , implying a low typical origin level. Precipitation conditionally averaged on decreases in surface equivalent potential temperature ( θ e ) exhibits a strong relationship because the most negative θ e values are associated with a high probability of precipitation. The more physically motivated conditional average of θ e on precipitation shows that decreases in θ e level off with increasing precipitation rate, bounded by the maximum difference between surface θ e and its minimum in the profile aloft. Robustness of these statistics observed across scales and regions suggests their potential use as model diagnostic tools for the improvement of downdraft parameterizations in climate models.

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Section: Downdraft Origin and The Effects Of Mixingmentioning

confidence: 56%

Tropical continental downdraft characteristics: mesoscale systems versus unorganized convection

Schiro

Neelin

2018

Atmos. Chem. Phys.

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“…Observations of warm downdrafts in the vicinity of convective storms at higher altitudes are presented by Fritsch (1975), who discusses observations by Sinclair (1973) made in the vicinity of severe storms at altitudes between 9 and 10 km AGL. The downward velocity within those were up to 5 m s 21 , and the entire downdraft had a horizontal extent of 13-km distance from the edge of the storm cloud.…”

Section: Discussionmentioning

confidence: 97%

“…It formed as a response to the upward mass flux associated with the convective updrafts. Observations of such compensatory downdrafts occurring in the mid-and upper troposphere have previously been presented and discussed by Sinclair (1973), Fritsch (1975), and Yuter and Houze (1995). We will present here measurements of the effects of such downdrafts on the lower troposphere.…”

Section: Introductionmentioning

confidence: 92%

Observations of Kinematics and Thermodynamic Structure Surrounding a Convective Storm Cluster over a Low Mountain Range

Groenemeijer

Barthlott

Behrendt

et al. 2009

Monthly Weather Review

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Measurements of a convective storm cluster in the northern Black Forest in southwest Germany have revealed the development of a warm and dry downdraft under its anvil cloud that had an inhibiting effect on the subsequent development of convection. These measurements were made on 12 July 2006 as part of the field campaign Prediction, Identification and Tracking of Convective Cells (PRINCE) during which a number of new measurement strategies were deployed. These included the collocation of a rotational Raman lidar and a Doppler lidar on the summit of the highest mountain in the region (1164 m MSL) as well as the deployment of teams carrying radiosondes to be released in the vicinity of convective storms. In addition, an aircraft equipped with sensors for meteorological variables and dropsondes was in operation and determined that the downdraft air was approximately 1.5 K warmer, 4 g kg 21 drier, and therefore 3 g m 23 less dense than the air at the same altitude in the storm's surroundings. The Raman lidar detected undulating aerosol-rich layers in the preconvective environment and a gradual warming trend of the lower troposphere as the nearby storm system evolved. The Doppler lidar both detected a pattern of convergent radial winds under a developing convective updraft and an outflow emerging under the storm's anvil cloud. The dryness of the downdraft air indicates that it had subsided from higher altitudes. Its low density reveals that its development was not caused by negative thermal buoyancy, but was rather due to the vertical mass flux balance accompanying the storm's updrafts.

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“…Cumulus clouds play an important role in weather and climate by maintaining the large-scale atmospheric circulation (e.g., Fritsch 1975;Emanuel et al 1994), transporting heat, moisture, and momentum in the atmosphere (Yanai et al 1973) and producing a multitude of clouds (e.g., Liu and Zipser 2005). Recent studies indicate the existence of distinct types of cumulus clouds in the tropics (e.g., Johnson et al 1999;Kumar et al 2013a).…”

Section: Introductionmentioning

confidence: 99%

Mass-Flux Characteristics of Tropical Cumulus Clouds from Wind Profiler Observations at Darwin, Australia

Kumar

Jakob

Protat

et al. 2015

Journal of the Atmospheric Sciences

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Cumulus parameterizations in weather and climate models frequently apply mass-flux schemes in their description of tropical convection. Mass flux constitutes the product of the fractional area covered by convection in a model grid box and the vertical velocity in cumulus clouds. However, vertical velocities are difficult to observe on GCM scales, making the evaluation of mass-flux schemes difficult. Here, the authors combine high-temporal-resolution observations of in-cloud vertical velocities derived from a pair of wind profilers over two wet seasons at Darwin with physical properties of precipitating clouds [cloud-top heights (CTH), convectivestratiform classification] derived from the Darwin C-band polarimetric radar to provide estimates of cumulus mass flux and its constituents. The length of this dataset allows for investigations of the contributions from different cumulus cloud types-namely, congestus, deep, and overshooting convection-to the overall mass flux and of the influence of large-scale conditions on mass flux. The authors found that mass flux was dominated by updrafts and, in particular, the updraft area fraction, with updraft vertical velocity playing a secondary role. The updraft vertical velocities peaked above 10 km where both the updraft area fractions and air densities were small, resulting in a marginal effect on mass-flux values. Downdraft area fractions are much smaller and velocities are much weaker than those in updrafts. The area fraction responded strongly to changes in midlevel large-scale vertical motion and convective inhibition (CIN). In contrast, changes in the lowertropospheric relative humidity and convective available potential energy (CAPE) strongly modulate in-cloud vertical velocities but have moderate impacts on area fractions. Although average mass flux is found to increase with increasing CTH, it is the environmental conditions that seem to dictate the magnitude of mass flux produced by convection through a combination of effects on area fraction and velocity.

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Cumulus dynamics: Local compensating subsidence and its implications for cumulus parameterization

Cited by 24 publications

References 27 publications

Tropical continental downdraft characteristics: mesoscale systems versus unorganized convection

Tropical continental downdraft characteristics: mesoscale systems versus unorganized convection

Observations of Kinematics and Thermodynamic Structure Surrounding a Convective Storm Cluster over a Low Mountain Range

Mass-Flux Characteristics of Tropical Cumulus Clouds from Wind Profiler Observations at Darwin, Australia

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