Convective environment in pre-monsoon and monsoon conditions over the Indian subcontinent: the impact of surface forcing

Thomas, Lois H; Malap, Neelam; Grabowski, Wojciech W.; Dani, K. K.; Prabha, Thara V.

doi:10.5194/acp-18-7473-2018

Cited by 25 publications

(20 citation statements)

References 43 publications

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“…This concerns not only the total flux but also its partitioning into sensible and latent components, which depends on the surface energy and water budgets. The partitioning significantly affects daytime convective development over land because it affects the surface buoyancy flux and boundary layer evolution (e.g., Thomas et al 2018).…”

Section: Discussionmentioning

confidence: 99%

Separating Dynamic and Thermodynamic Impacts of Climate Change on Daytime Convective Development over Land

Grabowski

Prein

2019

Journal of Climate

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Climate change affects the dynamics and thermodynamics of moist convection. Changes in the dynamics concern, for instance, an increase of convection strength due to increases of convective available potential energy (CAPE). Thermodynamics involve increases in water vapor that the warmer atmosphere can hold and convection can work with. Small-scale simulations are conducted to separate these two components for daytime development of unorganized convection over land. The simulations apply a novel modeling technique referred to as the piggybacking (or master–slave) approach and consider the global climate model (GCM)-predicted change of atmospheric temperature and moisture profiles in the Amazon region at the end of the century under a business-as-usual scenario. The simulations show that the dynamic impact dominates because changes in cloudiness and rainfall come from cloud dynamics considerations, such as the change in CAPE and convective inhibition (CIN) combined with the impact of environmental relative humidity (RH) on deep convection. The small RH reduction between the current and future climate significantly affects the mean surface rain accumulation as it changes from a small reduction to a small increase when the RH decrease is eliminated. The thermodynamic impact on cloudiness and precipitation is generally small, with the extreme rainfall intensifying much less than expected from an atmospheric moisture increase. These results are discussed in the context of previous studies concerning climate change–induced modifications of moist convection. Future research directions applying the piggybacking method are discussed.

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Section: Discussionmentioning

confidence: 99%

Separating Dynamic and Thermodynamic Impacts of Climate Change on Daytime Convective Development over Land

Grabowski

Prein

2019

Journal of Climate

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“…For small Bowen ratios, the latent heat flux is dominant over the sensible heat flux, and only about 10% of the total surface flux contributes to the buoyancy flux. For large Bowen ratios, almost all of the heat flux at surface contributes to the buoyancy flux (e.g., Thomas et al, 2018). In addition to the control on the buoyancy flux, the surface Bowen ratio also controls the limit up to which the heat flux at the surface can be converted into mechanical work of the convective circulations in the boundary layer (Shutts and Gray, 1999;Kleidon, 2016, sect.…”

Section: Discussionmentioning

confidence: 99%

Comparing ground‐based observations and a large‐eddy simulation of shallow cumuli by isolating the main controlling factors of the mass flux distribution

Sakradzija

Klingebiel

2019

Quart J Royal Meteoro Soc

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The distribution of mass flux at the cloud base has long been thought to be independent of large‐scale forcing. However, recent idealized modelling studies have revealed its dependence on some large‐scale conditions. Such dependence makes it possible to isolate the observed large‐scale conditions, which are similar to those in large‐eddy simulations (LES), in order to compare the observed and modelled mass flux distributions. In this study, we derive for the first time the distribution of the cloud‐base mass flux among individual shallow cumuli from ground‐based observations at the Barbados Cloud Observatory (BCO) and compare it with the Rain In Cumulus over the Ocean (RICO) LES case study. The procedure of cloud sampling in LES mimics the pointwise measurement procedure at the BCO to provide a mass flux metric that is directly comparable with observations. We find a difference between the mass flux distribution observed during the year 2017 at the BCO and the distribution modelled by LES that is comparable to the seasonal changes in the observed distribution. This difference between the observed and modelled distributions is diminished and an extremely good match is found by subsampling the measurements under a similar horizontal wind distribution and area‐averaged surface Bowen ratio to those modelled in LES. This provides confidence in our observational method and shows that LES produces realistic clouds that are comparable to those observed in nature under the same large‐scale conditions. We also confirm that the stronger horizontal winds and higher Bowen ratios in our case study shift the distributions to higher mass flux values, which is coincident with clouds of larger horizontal areas and not with stronger updrafts.

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“…Domain size of the model is 20 × 20 × 10 km 3 with a horizontal resolution of 100 m and vertical resolution of 50 m, similar to many previous studies (Thomas et al, ). Some model experiments were also carried out for larger domain size (30 × 30 × 15 km 3 ) and higher spatial resolution (30 m) and were found to have less impact on the results presented here.…”

Section: Model Setup and Soundingmentioning

confidence: 99%

Parameterization of Entrainment Rate and Mass Flux in Continental Cumulus Clouds: Inference From Large Eddy Simulation

Bera

Prabha

2019

JGR Atmospheres

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Large eddy simulation with contrasting environmental humidity is used to study entrainment and detrainment rates and convective mass flux during the development stages of continental deep cumulus clouds. The cumulus clouds studied here are deeper than marine shallow cumulus or stratocumulus in the published literature. The main objective of the study is to parameterize the entrainment and detrainment rates in monsoon clouds during the break monsoon periods over land, useful for the large‐scale atmospheric models. A systematic decrease in cloud liquid water path is noted in drier environments as clouds become shallower due to the reduction of positive buoyancy in the cloud core. Updraft and downdraft velocities in the subcloud layers are strengthened in the drier environments, which are found to affect in‐cloud updraft strength. A most important finding of the present study is the effect of environmental humidity on the entrainment (and detrainment) rates and the convective mass flux. Many previous studies on this topic reported opposite results. The present study found that decreasing environmental humidity leads to a decrease in both the entrainment rate and the convective mass flux but an increase in the detrainment rate. The relationship of the entrainment parameters with the environmental relative humidity can be used for parameterization in the large‐scale models. The physical mechanism responsible for such response is identified as the strengthening of the subcloud updrafts compensated by the enhanced downdraft into the boundary layer in the drier environments, and this mechanism subsequently led to higher in‐cloud updraft velocity, resulting in lower entrainment rate.

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Convective environment in pre-monsoon and monsoon conditions over the Indian subcontinent: the impact of surface forcing

Cited by 25 publications

References 43 publications

Separating Dynamic and Thermodynamic Impacts of Climate Change on Daytime Convective Development over Land

Separating Dynamic and Thermodynamic Impacts of Climate Change on Daytime Convective Development over Land

Comparing ground‐based observations and a large‐eddy simulation of shallow cumuli by isolating the main controlling factors of the mass flux distribution

Parameterization of Entrainment Rate and Mass Flux in Continental Cumulus Clouds: Inference From Large Eddy Simulation

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