TRMM-Observed Shallow versus Deep Convection in the Eastern Pacific Related to Large-Scale Circulations in Reanalysis Datasets

Yokoyama, Chie; Zipser, Edward J.; Liu, Chuntao

doi:10.1175/jcli-d-13-00315.1

Cited by 17 publications

(14 citation statements)

References 56 publications

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“…The Barbados Cloud Observatory data do, however, suggest that shallow circulations, driven in part by differential radiative cooling, are present in the tropical atmosphere and important for sustaining the contrast between the maritime trades and the Atlantic ITCZ. These findings fit well with previous observationally based studies, which have also argued for the importance of shallow circulations in explaining regions of moisture convergence and convection in the tropical atmosphere (Back and Bretherton 2009;Zhang et al 2004Zhang et al , 2008Yokoyama et al 2014). Our analysis goes one step further, however, as by performing the analysis in moisture space it suggests that mechanisms emerging in idealized simulations of radiative-convective equilibrium may also be relevant to explaining large-scale features of the maritime tropics.…”

Section: Discussionsupporting

confidence: 90%

Observing the Tropical Atmosphere in Moisture Space

Schulz

Stevens

2018

J. Atmos. Sci.

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Measurements from the Barbados Cloud Observatory are analyzed to identify the processes influencing the distribution of moist static energy and the large-scale organization of tropical convection. Five years of water vapor and cloud profiles from a Raman lidar and cloud radar are composed to construct the structure of the observed atmosphere in moisture space. The large-scale structure of the atmosphere is similar to that now familiar from idealized studies of convective self-aggregation, with shallow clouds prevailing over a moist marine layer in regions of low-rank humidity, and deep convection in a nearly saturated atmosphere in regions of high-rank humidity. With supplementary reanalysis datasets the overall circulation pattern is reconstructed in moisture space, and shows evidence of a substantial lower-tropospheric component to the circulation. This shallow component of the circulation helps support the differentiation between the moist and dry columns, similar to what is found in simulations of convective self-aggregation. Radiative calculations show that clear-sky radiative differences can explain a substantial part of this circulation, with further contributions expected from cloud radiative effects. The shallow component appears to be important for maintaining the low gross moist stability of the convecting column. A positive feedback between a shallow circulation driven by differential radiative cooling and the low-level moisture gradients that help support it is hypothesized to play an important role in conditioning the atmosphere for deep convection. The analysis suggests that the radiatively driven shallow circulations identified by modeling studies as contributing to the self-aggregation of convection in radiative–convective equilibrium similarly play a role in shaping the intertropical convergence zone and, hence, the large-scale structure of the tropical atmosphere.

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Section: Discussionsupporting

confidence: 90%

Observing the Tropical Atmosphere in Moisture Space

Schulz

Stevens

2018

J. Atmos. Sci.

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“…The population is associated with shallower echo heights but large rain areas Zipser 2009, 2013). We speculate the low-level forcing in the form of a large SST meridional gradient and associated shallow vertical circulation are uniquely important factors supporting these distinctive rain systems despite a dry middle troposphere (Yokoyama et al 2014;Chen and Liu 2016).…”

Section: ) Joint Distribution Of Large-system Rainfall Fraction Versmentioning

confidence: 91%

Relationships between Large Precipitating Systems and Atmospheric Factors at a Grid Scale

Chen

Liu

Mapes

2017

Journal of the Atmospheric Sciences

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In this study, TRMM-observed precipitation in the tropics is decomposed according to the horizontal area of radar precipitation features, with special emphasis on large systems (rain area > 104 km2) that contribute roughly half of tropical rainfall. Statistical associations of rain-weighted radar precipitation feature (RPF) size distributions with atmospheric variables on the 1.5° grid of ERA-Interim data are explored. In one-predictor distributions, the association with total precipitable water vapor (TPWV) is the strongest, while relative humidity at low and midlevels and low-level wind shear are also positively related to large-RPF rain fraction. Standard CAPE and CIN variables computed from grid-mean thermodynamic profiles are only weakly related to the size of rain systems. Joint distributions over two variables are also reported. The relative importance of predictors varies over different regions. The eastern Pacific is distinctive for having large rain systems in environments with a moist boundary layer but a dry midtroposphere, with strong shallow wind shear and small CAPE. In contrast, the large-storm environment over the western Pacific is found to be moister in the whole troposphere, with relatively weaker wind shear and larger CAPE. Over tropical land, the Sahel and central Africa stand out as having a great fractional rainfall contributed by large RPFs. Their associated environment is characterized by lower TPWV but stronger shallow wind shear and larger CIN and CAPE, in comparison to the equatorial Amazon basin and the Maritime Continent. Based on these associations, statistical reconstructions of the geographical distribution of large-RPF rain fraction from grid-mean atmospheric predictors are attempted.

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“…Over the eastern Pacific ITCZ, Zhang et al [2008] analyzed the seasonal cycle of the SMC using reanalysis data and reported that the SMC was the strongest during boreal fall. Yokoyama et al [2014] over the same region showed that the JRA reanalysis indicates less shallow return flow (deeper overall circulation) than the ERA Interim and MERRA [Rienecker et al, 2011] reanalyses. Handlos and Back [2014] reported a strong shallow return flow from an independent method based on energy conservation.…”

Section: Introductionmentioning

confidence: 89%

“…Yokoyama et al . [] over the same region showed that the JRA reanalysis indicates less shallow return flow (deeper overall circulation) than the ERA Interim and MERRA [ Rienecker et al ., ] reanalyses. Handlos and Back [] reported a strong shallow return flow from an independent method based on energy conservation.…”

Section: Introductionmentioning

confidence: 99%

Radiative driving of shallow return flows from the ITCZ

Nishant

Sherwood

2016

J Adv Model Earth Syst

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The tropical overturning circulation over the central-east Pacific not only extends through the troposphere but also includes a shallow component outflowing from the ITCZ near the planetary boundary layer (PBL) top, the Shallow Meridional Circulation (SMC). Idealized simulations with the Weather Research and Forecasting (WRF) model, which qualitatively reproduce this two-component circulation, are used to investigate the mechanism driving the SMC by altering model parameterization schemes (PBL, cumulus and radiation), the solar heating rate, and the SST gradient. A radiative-driving model for subsidence is tested and found to quantitatively predict the altitude and strength of the SMC in all experiments. This includes experiments with a changed SST gradient, in which the changes in temperature profile and clouds near PBL top in the subsiding region altered radiative cooling so as to make the SMC vary in proportion to the SST gradient. These results indicate that the SMC is strongly controlled by radiative cooling rather than independently by SST patterns or convective processes, at least in this model setup. Experiments with altered solar heating of the atmosphere affected the strength of the SMC strongly, while changes in cumulus parameterization had a weaker effect. Parameterization changes influenced the SMC mainly by altering shallow cloud amount and humidity in subsidence regions, but vertical gradients of temperature also affect the radiative driving of the SMC in at least one case. The results highlight that atmospheric radiative heating is of prime importance for determining the character of deep and shallow overturning.

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TRMM-Observed Shallow versus Deep Convection in the Eastern Pacific Related to Large-Scale Circulations in Reanalysis Datasets

Cited by 17 publications

References 56 publications

Observing the Tropical Atmosphere in Moisture Space

Observing the Tropical Atmosphere in Moisture Space

Relationships between Large Precipitating Systems and Atmospheric Factors at a Grid Scale

Radiative driving of shallow return flows from the ITCZ

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