Depression: Fighting the dragon

Ridout, Sue

doi:10.1037/e522822004-001

Cited by 2 publications

(4 citation statements)

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“…The significance of free-tropospheric humidity for convection is increasingly recognized (Raymond and Zeng 2000;Raymond 2000;Tompkins 2001a;Ridout 2002). These impacts are significant for large-scale modelling through the coupling to vertical motion (e.g.…”

Section: Discussionmentioning

confidence: 99%

“…For example, Ridout (2002) ran quasi-cloud-resolving-model forecasts of a case study within a nested framework, identified humidity impacts and compared with two parametrization schemes. The present study complements that work, using a more idealized case, much higher CRM resolution and a wider intercomparison of schemes geared to testing quantitatively their sensitivity to humidity.…”

Section: Introductionmentioning

confidence: 99%

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Sensitivity of moist convection to environmental humidity

Derbyshire

Beau

Bechtold

et al. 2004

Quart J Royal Meteoro Soc

418

391

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SUMMARYAs part of the EUROCS (EUROpean Cloud Systems study) project, cloud-resolving model (CRM) simulations and parallel single-column model (SCM) tests of the sensitivity of moist atmospheric convection to midtropospheric humidity are presented. This sensitivity is broadly supported by observations and some previous model studies, but is still poorly quantified. Mixing between clouds and environment is a key mechanism, central to many of the fundamental differences between convection schemes.Here, we define an idealized quasi-steady 'testbed', in which the large-scale environment is assumed to adjust the local mean profiles on a timescale of one hour. We then test sensitivity to the target profiles at heights above 2 km.Two independent CRMs agree reasonably well in their response to the different background profiles and both show strong deep precipitating convection in the more moist cases, but only shallow convection in the driest case. The CRM results also appear to be numerically robust. All the SCMs, most of which are one-dimensional versions of global climate models (GCMs), show sensitivity to humidity but differ in various ways from the CRMs. Some of the SCMs are improved in the light of these comparisons, with GCM improvements documented elsewhere.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Sensitivity of moist convection to environmental humidity

Derbyshire

Beau

Bechtold

et al. 2004

Quart J Royal Meteoro Soc

418

391

View full text Add to dashboard Cite

show abstract

“…Yanai et al 1973), and it has been highlighted in modelling studies of moist convection (e.g. Dudhia and Moncrieff 1987;Ridout 2002). On the mesoscale, individual convective clouds often form long-lasting groups or clumps, and one of possible explanations involves clouds moistening their immediate environment and rendering it more favourable for succeeding clouds (see a discussion by Randall and Huffman (1980)).…”

Section: Introductionmentioning

confidence: 99%

“…Johnson (1978) analysed Phase III GATE † data and showed that significant differences in observed convective development in response to the large-scale forcing can be explained through the differences in the free-tropospheric moisture stratification. Brown and Zhang (1997) analysed variability of moisture during TOGA COARE ‡ and speculated that advection of dry subtropical air was directly responsible for suppressing deep convection for a period of up to 10 days (see further discussion by Redelsperger et al (2002) and Ridout (2002), and references therein). Sherwood (1999) investigated conditions leading to convective outbreaks in the tropical western Pacific region and concluded that low-to mid-tropospheric moisture was the dominating factor.…”

Section: Introductionmentioning

confidence: 99%

Moisture–convection feedback in the tropics

Grabowski

Moncrieff

2004

Quart J Royal Meteoro Soc

145

111

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SUMMARYThis paper discusses the large-scale moisture-convection feedback in the tropics, where spatial fluctuations of deep convection cause perturbations of free-tropospheric moisture which, in turn, affect the spatial distribution of deep convection. A simple heuristic argument using the timescale of free-tropospheric humidity change explains why moisture-convection feedback is particularly relevant for tropical intraseasonal oscillations.The large-scale dynamical context for moisture-convection feedback is investigated in idealized rotating constant-sea-surface-temperature ('tropics everywhere') aquaplanet using cloud-resolving convection parametrization (CRCP; super-parametrization) and a traditional convective parametrization (the Emanuel scheme). The large-scale organization of convection within the equatorial waveguide takes the form of MJO-like (Madden-Julian Oscillation) coherent structures. First, CRCP simulations are performed in which development of large-scale free-tropospheric moisture perturbations is artificially suppressed using relaxation with a timescale of one day. As in previous simulations where much shorter relaxation timescale was used, MJO-like coherences do not develop and, if already present, they disintegrate rapidly. Second, CRCP simulations that start from planetaryscale moisture perturbation in the free troposphere are conducted. The ensuing large-scale velocity perturbations have e-folding times of five and seven days, respectively, for interactive and prescribed radiation simulations. This supports the conjecture that interactive radiation enhances moisture-convection feedback; an enhanced largescale circulation results from differences in radiative cooling between areas having enhanced and suppressed convectively-generated moisture and cloudiness. Additional support for the role of moisture-convection feedback in intraseasonal oscillations is seen in simulations that apply the Emanuel scheme. The standard configuration of the Emanuel scheme is insensitive to free-tropospheric humidity and results in weak MJO-like coherences. A simple modification of the Emanuel scheme that enhances its sensitivity to free-tropospheric humidity dramatically improves the simulated MJO-like coherences.

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Depression: Fighting the dragon

Cited by 2 publications

References 0 publications

Sensitivity of moist convection to environmental humidity

Sensitivity of moist convection to environmental humidity

Moisture–convection feedback in the tropics

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