A Satellite Study of the Atmospheric Forcing and Response to Moist Convection over Tropical and Subtropical Oceans

2012 ◽  
Vol 69 (1) ◽  
pp. 150-167 ◽  
Author(s):  
Hirohiko Masunaga
Keyword(s):  
Deep Convection ◽  
Convective Available Potential Energy ◽  
Tropical Rainfall Measuring Mission ◽  
Quasi Equilibrium ◽  
Tropospheric Temperature ◽  
Moist Convection ◽  
Atmospheric Forcing ◽  
Test Bed ◽  
Convective Adjustment ◽  
Subtropical Oceans

Abstract Satellite data are analyzed to explore the thermodynamic evolution of tropical and subtropical atmospheres prior and subsequent to moist convection in order to offer an observational test bed for convective adjustment, which is central to the quasi-equilibrium hypothesis. Tropical Rainfall Measuring Mission (TRMM) and Aqua satellite measurements are projected onto a composite temporal sequence over an hourly to daily time scale by exploiting the temporal gap between the local satellite overpasses, which changes from one day to another. The atmospheric forcing and response to convection are investigated separately for deep convective and congestus clouds. In the deep tropics, systematic moisture transport from the atmospheric boundary layer (ABL) to the free troposphere is evident in association with deep convection. The quick ABL ventilation suggests a swift convective adjustment but is preceded by a steady buildup of ABL moisture, which does not imply continuous adjustment to equilibrium. The evolution of convective available potential energy (CAPE) is controlled not only by the ABL moisture but also largely by a coincident ABL cooling linked with a bipolar anomaly of tropospheric temperature. The ABL moisture and temperature effects together lead to a rapid drop of CAPE for 12 h preceding convection, followed by a restoring phase that emerges as the cool anomaly recovers for a day or two. When moist convection is brought by congestus clouds with no deep convection nearby, CAPE gently increases over a period of 1–2 days until congestus occurs and then declines as slowly, suggestive of no efficient convective adjustment. The subtropical atmosphere shows no sign of convective adjustment whether or not vigorous convection is present.

scholarly journals A Unified Convection Scheme (UNICON). Part I: Formulation

2014 ◽  
Vol 71 (11) ◽  
pp. 3902-3930 ◽  
Author(s):  
Sungsu Park
Keyword(s):  
Deep Convection ◽  
Convective Available Potential Energy ◽  
Horizontal Resolution ◽  
Vertical Transport ◽  
Convective Precipitation ◽  
Cold Pool ◽  
Quasi Equilibrium ◽  
Convection Scheme ◽  
Time Step ◽  
Turbulent Eddies

Abstract The author develops a unified convection scheme (UNICON) that parameterizes relative (i.e., with respect to the grid-mean vertical flow) subgrid vertical transport by nonlocal asymmetric turbulent eddies. UNICON is a process-based model of subgrid convective plumes and mesoscale organized flow without relying on any quasi-equilibrium assumptions such as convective available potential energy (CAPE) or convective inhibition (CIN) closures. In combination with a relative subgrid vertical transport scheme by local symmetric turbulent eddies and a grid-scale advection scheme, UNICON simulates vertical transport of water species and conservative scalars without double counting at any horizontal resolution. UNICON simulates all dry–moist, forced–free, and shallow–deep convection within a single framework in a seamless, consistent, and unified way. It diagnoses the vertical profiles of the macrophysics (fractional area, plume radius, and number density) as well as the microphysics (production and evaporation rates of convective precipitation) and the dynamics (mass flux and vertical velocity) of multiple convective updraft and downdraft plumes. UNICON also prognoses subgrid cold pool and mesoscale organized flow within the planetary boundary layer (PBL) that is forced by evaporation of convective precipitation and accompanying convective downdrafts but damped by surface flux and entrainment at the PBL top. The combined subgrid parameterization of diagnostic convective updraft and downdraft plumes, prognostic subgrid mesoscale organized flow, and the feedback among them remedies the weakness of conventional quasi-steady diagnostic plume models—the lack of plume memory across the time step—allowing UNICON to successfully simulate various transitional phenomena associated with convection (e.g., the diurnal cycle of precipitation and the Madden–Julian oscillation).

Contribution of Tropical Cyclones to Global Very Deep Convection

2014 ◽  
Vol 27 (11) ◽  
pp. 4313-4336 ◽  
Author(s):  
Haiyan Jiang ◽  
Cheng Tao
Keyword(s):  
Tropical Cyclones ◽  
Deep Convection ◽  
Convective Available Potential Energy ◽  
Tropical Rainfall Measuring Mission ◽  
Precipitable Water ◽  
Moisture Exchange ◽  
Derived Properties ◽  
Trmm Precipitation ◽  
The Tropics ◽  
Heat And Moisture

Abstract Based on the 12-yr (1998–2009) Tropical Rainfall Measuring Mission (TRMM) precipitation feature (PF) database, both radar and infrared (IR) observations from TRMM are used to quantify the contribution of tropical cyclones (TCs) to very deep convection (VDC) in the tropics and to compare TRMM-derived properties of VDC in TCs and non-TCs. Using a radar-based definition, it is found that the contribution of TCs to total VDC in the tropics is not much higher than the contribution of TCs to total PFs. However, the area-based contribution of TCs to overshooting convection defined by IR is 13.3%, which is much higher than the 3.2% contribution of TCs to total PFs. This helps explain the contradictory results between previous radar-based and IR-based studies and indicates that TCs only contribute disproportionately large amount of overshooting convection containing mainly small ice particles that are barely detected by the TRMM radar. VDC in non-TCs over land has the highest maximum 30- and 40-dBZ height and the strongest ice-scattering signature derived from microwave 85- and 37-GHz observations, while VDC in TCs has the coldest minimum IR brightness temperature and largest overshooting distance and area. This suggests that convection is much more intense in non-TCs over land but is much deeper or colder in TCs. It is found that VDC in TCs usually has smaller environmental shear but larger total precipitable water and convective available potential energy than those in non-TCs. These findings offer evidence that TCs may contribute disproportionately to troposphere-to-stratosphere heat and moisture exchange.

scholarly journals Shallow and Deep Latent Heating Modes over Tropical Oceans Observed with TRMM PR Spectral Latent Heating Data

2010 ◽  
Vol 23 (8) ◽  
pp. 2030-2046 ◽  
Author(s):  
Yukari N. Takayabu ◽  
Shoichi Shige ◽  
Wei-Kuo Tao ◽  
Nagio Hirota
Keyword(s):  
Large Scale ◽  
Deep Convection ◽  
Three Dimensional ◽  
Tropical Rainfall Measuring Mission ◽  
Radiative Heating ◽  
Latent Heating ◽  
Tropical Oceans ◽  
Trmm Precipitation ◽  
Subtropical Oceans ◽  
Cumulus Congestus

Abstract Three-dimensional distributions of the apparent heat source (Q1) − radiative heating (QR) estimated from Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) utilizing the spectral latent heating (SLH) algorithm are analyzed. Mass-weighted and vertically integrated Q1 − QR averaged over the tropical oceans is estimated as ∼72.6 J s−1 (∼2.51 mm day−1) and that over tropical land is ∼73.7 J s−1 (∼2.55 mm day−1) for 30°N–30°S. It is shown that nondrizzle precipitation over tropical and subtropical oceans consists of two dominant modes of rainfall systems: deep systems and congestus. A rough estimate of the shallow-heating contribution against the total heating is about 46.7% for the average tropical oceans, which is substantially larger than the 23.7% over tropical land. Although cumulus congestus heating linearly correlates with SST, deep-mode heating is dynamically bounded by large-scale subsidence. It is notable that a substantial amount of rain, as large as 2.38 mm day−1 on average, is brought from congestus clouds under the large-scale subsiding circulation. It is also notable that, even in the region with SSTs warmer than 28°C, large-scale subsidence effectively suppresses the deep convection, with the remaining heating by congestus clouds. The results support that the entrainment of mid–lower-tropospheric dry air, which accompanies the large-scale subsidence, is the major factor suppressing the deep convection. Therefore, a representation of the realistic entrainment is very important for proper reproduction of precipitation distribution and the resultant large-scale circulation.

scholarly journals Response of Tropical Deep Convection to Localized Heating Perturbations: Implications for Aerosol-Induced Convective Invigoration

2013 ◽  
Vol 70 (11) ◽  
pp. 3533-3555 ◽  
Author(s):  
Hugh Morrison ◽  
Wojciech W. Grabowski
Keyword(s):  
Large Scale ◽  
Deep Convection ◽  
Warm Pool ◽  
Tropospheric Temperature ◽  
Surface Precipitation ◽  
Tropical Warm Pool ◽  
Adjustment Time ◽  
Localized Heating ◽  
Tropical Deep Convection ◽  
Convective Adjustment

Abstract A cloud-system-resolving model is used to investigate the effects of localized heating/cooling perturbations on tropical deep convection, in the context of the aerosol “invigoration effect.” This effect supposes that a reduction of droplet collision–coalescence in polluted conditions leads to lofting of cloud water in convective updrafts and enhanced freezing, latent heating, and buoyancy. To specifically isolate and test this mechanism, heating perturbations were applied to updrafts with corresponding cooling applied in downdrafts. Ensemble simulations were run with either perturbed or unperturbed conditions and large-scale forcing from a 7.5-day period of active monsoon conditions during the 2006 Tropical Warm Pool–International Cloud Experiment. In the perturbed simulations there was an initial invigoration of convective updrafts and surface precipitation, but convection returned to its unperturbed state after about 24 h because of feedback with the larger-scale environment. This feedback led to an increase in the horizontally averaged mid-/upper-tropospheric temperature of about 1 K relative to unperturbed simulations. When perturbed conditions were applied to only part of the domain, gravity waves rapidly dispersed buoyancy anomalies in the perturbed region to the rest of the domain, allowing convective invigoration from the heating perturbations to be sustained over the entire simulation period. This was associated with a mean mesoscale circulation consisting of ascent (descent) at mid-/upper levels in the perturbed (unperturbed) region. In contrast to recent studies, it is concluded that the invigoration effect is intimately coupled with larger-scale dynamics through a two-way feedback, and in the absence of alterations in the larger-scale circulation there is limited invigoration beyond the convective adjustment time scale.

scholarly journals Radiosonde observations of environments supporting deep moist convection initiation during RELAMPAGO-CACTI

2020 ◽  
Author(s):  
T. Connor Nelson ◽  
James Marquis ◽  
Adam Varble ◽  
Katja Friedrich
Keyword(s):  
Complex Terrain ◽  
Deep Convection ◽  
Convective Available Potential Energy ◽  
Environmental Parameters ◽  
Convective Precipitation ◽  
Moist Convection ◽  
Spatiotemporal Resolution ◽  
Close Proximity ◽  
Deep Moist Convection ◽  
Convection Initiation

AbstractThe Remote Sensing of Electrification, Lightning, and Mesoscale/Microscale Processes with Adaptive Ground Observations (RELAMPAGO) and Cloud, Aerosol, and Complex Terrain Interactions (CACTI) projects deployed a high-spatiotemporal-resolution radiosonde network to examine environments supporting deep convection in the complex terrain of central Argentina. This study aims to characterize atmospheric profiles most representative of the near-cloud environment (in time and space) to identify the mesoscale ingredients affecting storm initiation and growth. Spatiotemporal autocorrelation analysis of the soundings reveals that there is considerable environmental heterogeneity, with boundary layer thermodynamic and kinematic fields becoming statistically uncorrelated on scales of 1–2 hr and 30 km. Using this as guidance, we examine a variety of environmental parameters derived from soundings collected within close proximity (30 km and 30 min in space and time) of 44 events over 9 days where the atmosphere either: 1) supported the initiation of sustained precipitating convection, 2) yielded weak and short-lived precipitating convection, or 3) produced no precipitating convection in disagreement with numerical forecasts from convection-allowing models (i.e., Null events). There are large statistical differences between the Null event environments and those supporting any convective precipitation. Null event profiles contained larger convective available potential energy, but had low free tropospheric relative humidity, higher freezing levels, and evidence of limited horizontal convergence near the terrain at low levels that likely suppressed deep convective growth. We also present evidence from the radiosonde and satellite measurements that flow-terrain interactions may yield gravity wave activity that affects CI outcome.

scholarly journals Low-level Mesoscale and Cloud-scale Interactions Promoting Deep Convection Initiation

2021 ◽  
Author(s):  
James N. Marquis ◽  
Adam C. Varble ◽  
Paul Robinson ◽  
T. Connor. Nelson ◽  
Katja Friedrich
Keyword(s):  
Boundary Layer ◽  
Deep Convection ◽  
Convective Available Potential Energy ◽  
Surface Wind ◽  
Horizontal Wind ◽  
Moist Convection ◽  
Surface Precipitation ◽  
Low Level ◽  
Deep Moist Convection ◽  
Convection Initiation

AbstractData from scanning radars, radiosondes, and vertical profilers deployed during three field campaigns are analyzed to study interactions between cloud-scale updrafts associated with initiating deep moist convection and the surrounding environment. Three cases are analyzed in which the radar networks permitted dual-Doppler wind retrievals in clear air preceding and during the onset of surface precipitation. These observations capture the evolution of: i) the mesoscale and boundary layer flow, and ii) low-level updrafts associated with deep moist convection initiation (CI) events yielding sustained or short-lived precipitating storms.The elimination of convective inhibition did not distinguish between sustained and unsustained CI events, though the vertical distribution of convective available potential energy may have played a role. The clearest signal differentiating the initiation of sustained versus unsustained precipitating deep convection was the depth of the low-level horizontal wind convergence associated with the mesoscale flow feature triggering CI, a sharp surface wind shift boundary or orographic upslope flow. The depth of the boundary layer relative to the height of the LFC failed to be a consistent indicator of CI potential. Widths of the earliest detectable low-level updrafts associated with sustained precipitating deep convection were ~3-5 km, larger than updrafts associated with surrounding boundary layer turbulence (~1-3-km wide). It is hypothesized that updrafts of this larger size are important for initiating cells to survive the destructive effects of buoyancy dilution via entrainment.

scholarly journals A Transilient Matrix for Moist Convection

2011 ◽  
Vol 68 (9) ◽  
pp. 2009-2025 ◽  
Author(s):  
David M. Romps ◽  
Zhiming Kuang
Keyword(s):  
Potential Energy ◽  
Deep Convection ◽  
Convective Available Potential Energy ◽  
Free Troposphere ◽  
Moist Convection ◽  
Initial Height ◽  
Available Potential Energy ◽  
Tropical Troposphere ◽  
Nonlocal Transport

Abstract A method is introduced for diagnosing a transilient matrix for moist convection. This transilient matrix quantifies the nonlocal transport of air by convective eddies: for every height z, it gives the distribution of starting heights z′ for the eddies that arrive at z. In a cloud-resolving simulation of deep convection, the transilient matrix shows that two-thirds of the subcloud air convecting into the free troposphere originates from within 100 m of the surface. This finding clarifies which initial height to use when calculating convective available potential energy from soundings of the tropical troposphere.

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

2019 ◽  
Vol 32 (16) ◽  
pp. 5213-5234 ◽  
Author(s):  
Wojciech W. Grabowski ◽  
Andreas F. Prein
Keyword(s):  
Climate Change ◽  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Deep Convection ◽  
Convective Available Potential Energy ◽  
Future Research ◽  
Small Scale ◽  
Moist Convection ◽  
The Impact

AbstractClimate 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.

scholarly journals Is the Tropical Atmosphere in Convective Quasi-Equilibrium?

2015 ◽  
Vol 28 (11) ◽  
pp. 4357-4372 ◽  
Author(s):  
Jia-Lin Lin ◽  
Taotao Qian ◽  
Toshiaki Shinoda ◽  
Shuanglin Li
Keyword(s):  
Boundary Layer ◽  
Global Climate Models ◽  
Quasi Equilibrium ◽  
Tropical Atmosphere ◽  
Tropospheric Temperature ◽  
Moist Convection ◽  
Moist Static Energy ◽  
Shallow Convection ◽  
Upper Troposphere ◽  
Static Energy

Abstract The hypothesis of convective quasi-equilibrium (CQE) has dominated thinking about the interaction between deep moist convection and the environment for at least two decades. In this view, deep convection develops or decays almost instantly to remove any changes of convective instability, making the tropospheric temperature always tied to the boundary layer moist static energy. The present study examines the validity of the CQE hypothesis at different vertical levels using long-term sounding data from tropical convection centers. The results show that the tropical atmosphere is far from the CQE with much weaker warming in the middle and upper troposphere associated with the increase of boundary layer moist static energy. This is true for all the time scales resolved by the observational data, ranging from hourly to interannual and decadal variability. It is possibly caused by the ubiquitous existence of shallow convection and stratiform precipitation, both leading to sign reversal of heating from lower to upper troposphere. The simulations by 42 global climate models from phases 3 and 5 of the Coupled Model Intercomparsion Project (CMIP3 and CMIP5) are also analyzed and compared with the observations.

Adjustment of the Remote Tropical Climate to El Niño Conditions

2007 ◽  
Vol 20 (11) ◽  
pp. 2544-2557 ◽  
Author(s):  
Benjamin R. Lintner ◽  
John C. H. Chiang
Keyword(s):  
El Niño ◽  
El Nino ◽  
Deep Convection ◽  
Thermal Inertia ◽  
Tropical Climate ◽  
Abrupt Onset ◽  
Convective Precipitation ◽  
Quasi Equilibrium ◽  
Moist Convection ◽  
Vertical Coupling

Abstract The adjustment of the tropical climate outside the Pacific (the “remote Tropics”) to the abrupt onset of El Niño conditions is examined in a tropical atmosphere model that assumes simplified vertical structure and quasi-equilibrium (QE) convective closure. The El Niño signal is rapidly (∼1 week) communicated to the remote Tropics via an eastward-propagating Kelvin-like wave that induces both anomalous subsidence and tropospheric warming. Widespread reductions in convective precipitation occur in conjunction with the spreading of the temperature and subsidence anomalies. The remote rainfall suppression peaks roughly 5–15 days after the initiation of El Niño conditions, after which the anomalous remote rainfall field recovers to a state characterized by a smaller remote areal mean rainfall deficit and the appearance of localized positive rainfall anomalies. The initial remote precipitation reduction after El Niño onset is tied to both tropospheric warming (i.e., stabilization of the troposphere to deep convection) and the suppression of remote humidity levels; recovery of the initial deficits occurs as feedbacks modulate the subsequent evolution of humidity anomalies in the tropospheric column. Apart from the short-term response, there is a longer-term adjustment of the remote climate related to the thermal inertia of the underlying surface: surface thermal disequilibrium, which is related to the depth of the ocean mixed layer, maintains larger precipitation deficits than would be expected for equilibrated conditions. This result supports a previous prediction by one of the authors for a significant disequilibrium mechanism in the precipitation teleconnection to El Niño resulting from the local vertical coupling of the troposphere to the surface through moist convection.

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