scholarly journals The Sensitivity of Convective Initiation to the Lapse Rate of the Active Cloud-Bearing Layer

2007 ◽  
Vol 135 (9) ◽  
pp. 3013-3032 ◽  
Author(s):  
Adam L. Houston ◽  
Dev Niyogi
Keyword(s):  
Thermal Instability ◽  
Deep Convection ◽  
Lapse Rate ◽  
Lagrangian Model ◽  
Subcritical State ◽  
State Variables ◽  
Convective Initiation ◽  
Rate Of Increase ◽  
Lapse Rates ◽  
Bearing Layer

Abstract Numerical experiments are conducted using an idealized cloud-resolving model to explore the sensitivity of deep convective initiation (DCI) to the lapse rate of the active cloud-bearing layer [ACBL; the atmospheric layer above the level of free convection (LFC)]. Clouds are initiated using a new technique that involves a preexisting airmass boundary initialized such that the (unrealistic) adjustment of the model state variables to the imposed boundary is disassociated from the simulation of convection. Reference state environments used in the experiment suite have identical mixed layer values of convective inhibition, CAPE, and LFC as well as identical profiles of relative humidity and wind. Of the six simulations conducted for the experiment set, only the three environments with the largest ACBL lapse rates support DCI. The simulated deep convection is initiated from elevated sources (parcels in the convective clouds originate near 1300 m) despite the presence of a surface-based boundary. Thermal instability release is found to be more likely in the experiments with larger ACBL lapse rates because the forced ascent at the preexisting boundary is stronger (despite nearly identical boundary depths) and because the parcels’ LFCs are lower, irrespective of parcel dilution. In one experiment without deep convection, DCI failure occurs even though thermal instability is released. Results from this experiment along with the results from a heuristic Lagrangian model reveal the existence of two convective regimes dependent on the environmental lapse rate: a supercritical state capable of supporting DCI and a subcritical state that is unlikely to support DCI. Under supercritical conditions the rate of increase in buoyancy due to parcel ascent exceeds the reduction in buoyancy due to dilution. Under subcritical conditions, the rate of increase in buoyancy due to parcel ascent is outpaced by the rate of reduction in buoyancy from dilution. Overall, results demonstrate that the lapse rate of the ACBL is useful in diagnosing and/or predicting DCI.

scholarly journals Observing Possible Thermodynamic Controls on Tropical Marine Rainfall in Moist Environments

2019 ◽  
Vol 76 (12) ◽  
pp. 3737-3751 ◽  
Author(s):  
Scott W. Powell
Keyword(s):  
Rain Rate ◽  
Environmental Influence ◽  
Spatial Scales ◽  
Deep Convection ◽  
Lapse Rate ◽  
State Variables ◽  
Convective Rainfall ◽  
Areal Coverage ◽  
Wide Range ◽  
Rawinsonde Data

Abstract Radar and rawinsonde data from four ground-based observing stations in the tropical Indo-Pacific warm pool were used to identify possible associations of environmental state variables and their vertical profiles with radar-derived rain rate inside a mesoscale radar domain when the column-integrated relative humidity (CRH) exceeds 80%. At CRH exceeding 80%, a wide range—from near 0 to ~50 mm day−1—in rain rate is observed; therefore, tropospheric moisture was a necessary but insufficient condition for deep convection. This study seeks to identify possible factors that inhibit rainfall when the atmosphere is sufficiently moist to support large precipitation rates. The domain-mean rain rate was highly sensitive to the areal coverage of intense, convective rainfall that occurs. There were two fundamentally different instances in which convective area was low. One was when the radar domain is primarily occupied by weakly precipitating, stratiform echoes. The other was when the radar domain contained almost no precipitating echoes of any type. While the former was dependent upon the stage of the convective life cycle seen by radar, the latter was probably dependent upon the convective environment. Areal coverage of convective echoes was largely determined by the number of individual convective echoes rather than their sizes, so changes in the clear-air environment of updrafts might have governed how many updrafts grew into deep cumulonimbi. The most likely environmental influence on convective rainfall identified using rawinsonde data was 900–700-hPa lapse rate; however, processes occurring on spatial scales smaller than a radar domain were probably also important but not investigated.

Influences of environmental relative humidity and horizontal scale of sub-cloud ascent on deep convective initiation

2021 ◽  
Author(s):  
Hugh Morrison ◽  
John M. Peters ◽  
Kamal Kant Chandakar ◽  
Steven C. Sherwood
Keyword(s):  
Relative Humidity ◽  
Deep Convection ◽  
Threshold Value ◽  
Surface Fluxes ◽  
Lapse Rate ◽  
Entrainment Rate ◽  
Moist Convection ◽  
Convective Initiation ◽  
Two Factors ◽  
Environmental Relative Humidity

AbstractThis study examines two factors impacting initiation of moist deep convection: free tropospheric environmental relative humidity (ϕE) and horizon scale of sub-cloud ascent (Rsub), the latter exerting a dominant control on cumulus cloud width. A simple theoretical model is used to formulate a “scale selection” hypothesis: that a minimum Rsub is required for moist convection to go deep, and that this minimum scale decreases with increasing ϕE. Specifically, the ratio of to saturation deficit (1–ϕE) must exceed a certain threshold value that depends on cloud-layer environmental lapse rate. Idealized, large-eddy simulations of moist convection forced by horizontally-varying surface fluxes show strong sensitivity of maximum cumulus height to both ϕE and Rsub consistent with the hypothesis. Increasing Rsub by only 300-400 m can lead to a large increase (> 5 km) in cloud height. A passive tracer analysis shows that the bulk fractional entrainment rate decreases rapidly with Rsub but depends little on ϕE. However, buoyancy dilution increases as either Rsub or ϕE decreases; buoyancy above the level of free convection is rapidly depleted in dry environments when Rsub is small. While deep convective initiation occurs with an increase in relative humidity of the near environment from moistening by earlier convection, the importance of this moisture preconditioning is inconclusive as it is accompanied by an increase in Rsub. Overall, it is concluded that small changes to Rsub driven by external forcing or by convection itself could be a dominant regulator of deep convective initiation.

scholarly journals Thermal structure of intense convective clouds derived from GPS radio occultations

2012 ◽  
Vol 12 (12) ◽  
pp. 5309-5318 ◽  
Author(s):  
R. Biondi ◽  
W. J. Randel ◽  
S.-P. Ho ◽  
T. Neubert ◽  
S. Syndergaard
Keyword(s):  
Thermal Structure ◽  
Deep Convection ◽  
Lapse Rate ◽  
Orthogonal Polarization ◽  
Cold Temperatures ◽  
Temperature Lapse Rate ◽  
Convective Systems ◽  
Convective Clouds ◽  
Strong Inversion ◽  
Cloud Tops

Abstract. Thermal structure associated with deep convective clouds is investigated using Global Positioning System (GPS) radio occultation measurements. GPS data are insensitive to the presence of clouds, and provide high vertical resolution and high accuracy measurements to identify associated temperature behavior. Deep convective systems are identified using International Satellite Cloud Climatology Project (ISCCP) satellite data, and cloud tops are accurately measured using Cloud-Aerosol Lidar with Orthogonal Polarization (CALIPSO) lidar observations; we focus on 53 cases of near-coincident GPS occultations with CALIPSO profiles over deep convection. Results show a sharp spike in GPS bending angle highly correlated to the top of the clouds, corresponding to anomalously cold temperatures within the clouds. Above the clouds the temperatures return to background conditions, and there is a strong inversion at cloud top. For cloud tops below 14 km, the temperature lapse rate within the cloud often approaches a moist adiabat, consistent with rapid undiluted ascent within the convective systems.

scholarly journals Buoyant Motion in a Turbulent Environment

1953 ◽  
Vol 6 (3) ◽  
pp. 279 ◽  
Author(s):  
CHB Priestley
Keyword(s):  
Vertical Velocity ◽  
Initial Conditions ◽  
Simultaneous Equations ◽  
Lapse Rate ◽  
Turbulent Environment ◽  
Continuous Mixing ◽  
Ascent Rate ◽  
Damped Oscillations ◽  
Equilibrium Level ◽  
Lapse Rates

Solutions are given of the simultaneous equations for the vertical velocity and temperature of an element of fluid moving under buoyancy and subject to continuous mixing of heat and momentum with its environment. Three distinct modes of behaviour result: (A) ascent followed by damped oscillations, (B) asymptotic ascent to an equilibrium level, (C) absolute buoyancy in which the ascent rate increases indefinitely. For an environment in which the lapse rate is subadiabatic the motion is of type A for sufficiently large elements but may become B for the smaller elements; in super-adiabatic lapse rates the mode is C for sufficiently large elements, and B for the smaller elements, which are in no way unstable. The mode of motion is independent of the initial conditions but the scale of the motion is not.

scholarly journals Effect of deep convection on the TTL composition over the Southwest Indian Ocean during austral summer

2020 ◽  
Author(s):  
Stephanie Evan ◽  
Jerome Brioude ◽  
Karen Rosenlof ◽  
Sean M. Davis ◽  
Hölger Vömel ◽  
...  
Keyword(s):  
Water Vapor ◽  
Indian Ocean ◽  
Tropical Cyclones ◽  
Deep Convection ◽  
Austral Summer ◽  
Active Regions ◽  
Lagrangian Model ◽  
Southwest Indian Ocean ◽  
Tropopause Region ◽  
The Impact

Abstract. Balloon-borne measurements of CFH water vapor, ozone and temperature and water vapor lidar measurements from the Maïdo Observatory at Réunion Island in the Southwest Indian Ocean (SWIO) were used to study tropical cyclones' influence on TTL composition. The balloon launches were specifically planned using a Lagrangian model and METEOSAT 7 infrared images to sample the convective outflow from Tropical Storm (TS) Corentin on 25 January 2016 and Tropical Cyclone (TC) Enawo on 3 March 2017. Comparing CFH profile to MLS monthly climatologies, water vapor anomalies were identified. Positive anomalies of water vapor and temperature, and negative anomalies of ozone between 12 and 15 km in altitude (247 to 121 hPa) originated from convectively active regions of TS Corentin and TC Enawo, one day before the planned balloon launches, according to the Lagrangian trajectories. Near the tropopause region, air masses on 25 January 2016 were anomalously dry around 100 hPa and were traced back to TS Corentin active convective region where cirrus clouds and deep convective clouds may have dried the layer. An anomalously wet layer around 68 hPa was traced back to the South East IO where a monthly water vapor anomaly of 0.5 ppbv was observed. In contrast, no water vapor anomaly was found near or above the tropopause region on 3 March 2017 over Maïdo as the tropopause region was not downwind of TC Enawo. This study compares and contrasts the impact of two tropical cyclones on the humidification of the TTL over the Southwest Indian Ocean.

The Optical Measurement of Lapse Rate *

1950 ◽  
Vol 31 (2) ◽  
pp. 51-55 ◽  
Author(s):  
Robert G. Fleagle
Keyword(s):  
Optical Measurement ◽  
Vertical Gradient ◽  
Lapse Rate ◽  
Speed Of Light ◽  
Indirect Methods ◽  
Reliable Determination ◽  
Air Density ◽  
Lapse Rates ◽  
The Relationship

The need for reliable determination of the temperature of the air very near the ground and the difficulties inherent in measurement of this quantity by the ordinary indirect methods are pointed out. It is suggested that the dependence of the speed of light on air density provides a convenient method for the determination of the temperature near the ground by direct measurement of the lapse rate, and evidence is given from other papers to show that this is feasible where the vertical gradient of humidity is not great. The relationship between apparent elevation and lapse rates of temperature and vapor pressure is derived, and the relationship is illustrated by the results of computations.

scholarly journals Intraseasonal Variability in MERRA Energy Fluxes over the Tropical Oceans

2012 ◽  
Vol 25 (17) ◽  
pp. 5629-5647 ◽  
Author(s):  
Franklin R. Robertson ◽  
Jason B. Roberts
Keyword(s):  
Deep Convection ◽  
Intraseasonal Variability ◽  
Tropical Rainfall Measuring Mission ◽  
Precipitation Anomaly ◽  
Surface Fluxes ◽  
State Variables ◽  
Cloud Forcing ◽  
Tropical Oceans ◽  
Fractional Cloud ◽  
Moderate Resolution Imaging Spectroradiometer

Abstract This paper investigates intraseasonal variability as represented by the recent NASA Global Modeling and Assimilation Office (GMAO) reanalysis, the Modern-Era Retrospective analysis for Research and Applications (MERRA). The authors examine the behavior of heat, moisture, and radiative fluxes emphasizing their contribution to intraseasonal variations in heat and moisture balance integrated over the tropical oceans. MERRA successfully captures intraseasonal signals in both state variables and fluxes, though it depends heavily on the analysis increment update terms that constrain the reanalysis to be near the observations. Precipitation anomaly patterns evolve in close agreement with those from the Tropical Rainfall Measuring Mission (TRMM) though locally MERRA may occasionally be smaller by up to 20%. As in the TRMM observations, tropical convection increases lead tropospheric warming by approximately 7 days. Radiative flux anomalies are dominated by cloud forcing and are found to replicate the top-of-the-atmosphere (TOA) energy loss associated with increased convection found by other observationally based studies. However, MERRA’s convectively produced clouds appear to deepen too soon as precipitation increases. Total fractional cloud cover variations appear somewhat weak compared to observations from the Moderate Resolution Imaging Spectroradiometer (MODIS). Evolution of the surface fluxes, convection, and TOA radiation is consistent with the “discharge–recharge” paradigm that posits the importance of lower-tropospheric moisture accumulation prior to the expansion of organized deep convection. The authors conclude that MERRA constitutes a very useful representation of intraseasonal variability that will support a variety of studies concerning radiative–convective–dynamical processes and will help identify pathways for improved moist physical parameterization in global models.

The Atmospheric Energy Constraint on Global-Mean Precipitation Change

2014 ◽  
Vol 27 (2) ◽  
pp. 757-768 ◽  
Author(s):  
Angeline G. Pendergrass ◽  
Dennis L. Hartmann
Keyword(s):  
Water Vapor ◽  
Temperature Increase ◽  
Longwave Radiation ◽  
Surface Fluxes ◽  
Lapse Rate ◽  
Specific Humidity ◽  
Radiative Cooling ◽  
Rate Of Increase ◽  
Precipitation Increase ◽  
Global Mean

Abstract Models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) robustly predict that the rate of increase in global-mean precipitation with global-mean surface temperature increase is much less than the rate of increase of water vapor. The goal of this paper is to explain in detail the mechanisms by which precipitation increase is constrained by radiative cooling. Changes in clear-sky atmospheric radiative cooling resulting from changes in temperature and humidity in global warming simulations are in good agreement with the multimodel, global-mean precipitation increase projected by GCMs (~1.1 W m−2 K−1). In an atmosphere with fixed specific humidity, radiative cooling from the top of the atmosphere (TOA) increases in response to a uniform temperature increase of the surface and atmosphere, while atmospheric cooling by exchange with the surface decreases because the upward emission of longwave radiation from the surface increases more than the downward longwave radiation from the atmosphere. When a fixed relative humidity (RH) assumption is made, however, uniform warming causes a much smaller increase of cooling at the TOA, and the surface contribution reverses to an increase in net cooling rate due to increased downward emission from water vapor. Sensitivity of precipitation changes to lapse rate changes is modest when RH is fixed. Carbon dioxide reduces TOA emission with only weak effects on surface fluxes, and thus suppresses precipitation. The net atmospheric cooling response and thereby the precipitation response to CO2-induced warming at fixed RH are mostly contributed by changes in surface fluxes. The role of clouds is discussed. Intermodel spread in the rate of precipitation increase across the CMIP5 simulations is attributed to differences in the atmospheric cooling.

scholarly journals Neutral Saturated Lapse Rate: An Experimental Check from CALJET-1998 and PACJET-2001

2009 ◽  
Vol 137 (12) ◽  
pp. 4382-4385 ◽  
Author(s):  
Renzo Richiardone ◽  
Massimiliano Manfrin
Keyword(s):  
High Resolution ◽  
Normal Distribution ◽  
Mean Value ◽  
Lapse Rate ◽  
Temperature Profiles ◽  
Experimental Check ◽  
Rate Distribution ◽  
The Mean ◽  
Lapse Rates ◽  
Good Agreement

Abstract The lapse rates of high-resolution temperature profiles during nearly neutral, saturated conditions are compared with the saturated adiabatic lapse rate and with that proposed by Richiardone and Giusti. A good agreement between the latter and the mean value of the observed lapse rate is found, whereas the saturated adiabatic lapse rate differs significantly, confirming experimentally that it is not completely correct to assess the moist neutrality from a comparison with the saturated adiabatic lapse rate. The lapse-rate distribution supports the hypothesis that the lapse-rate statistics is a local collection of saturated adiabatic lapse rates in a background normal distribution centered around the neutrality.

scholarly journals The Dryline on 22 May 2002 during IHOP_2002: Convective-Scale Measurements at the Profiling Site

2006 ◽  
Vol 134 (1) ◽  
pp. 294-310 ◽  
Author(s):  
Belay Demoz ◽  
Cyrille Flamant ◽  
Tammy Weckwerth ◽  
David Whiteman ◽  
Keith Evans ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Continuous Wave ◽  
Doppler Radar ◽  
Layer Structure ◽  
Deep Convection ◽  
Radiosonde Data ◽  
Small Scale ◽  
Convective Initiation ◽  
Near Surface ◽  
Fine Line

Abstract A detailed analysis of the structure of a double dryline observed over the Oklahoma panhandle during the first International H2O Project (IHOP_2002) convective initiation (CI) mission on 22 May 2002 is presented. A unique and unprecedented set of high temporal and spatial resolution measurements of water vapor mixing ratio, wind, and boundary layer structure parameters were acquired using the National Aeronautics and Space Administration (NASA) scanning Raman lidar (SRL), the Goddard Lidar Observatory for Winds (GLOW), and the Holographic Airborne Rotating Lidar Instrument Experiment (HARLIE), respectively. These measurements are combined with the vertical velocity measurements derived from the National Center for Atmospheric Research (NCAR) Multiple Antenna Profiler Radar (MAPR) and radar structure function from the high-resolution University of Massachusetts frequency-modulated continuous-wave (FMCW) radar to reveal the evolution and structure of the late afternoon double-dryline boundary layer. The eastern dryline advanced and then retreated over the Homestead profiling site in the Oklahoma panhandle, providing conditions ripe for a detailed observation of the small-scale variability within the boundary layer and the dryline. In situ aircraft data, dropsonde and radiosonde data, along with NCAR S-band dual-polarization Doppler radar (S-Pol) measurements, are also used to provide the larger-scale picture of the double-dryline environment. Moisture and temperature jumps of about 3 g kg−1 and 1–2 K, respectively, were observed across the eastern radar fine line (dryline), more than the moisture jumps (1–2 g kg−1) observed across the western radar fine line (secondary dryline). Most updraft plumes observed were located on the moist side of the eastern dryline with vertical velocities exceeding 3 m s−1 and variable horizontal widths of 2–5 km, although some were as wide as 7–8 km. These updrafts were up to 1.5 g kg−1 moister than the surrounding environment. Although models suggested deep convection over the Oklahoma panhandle and several cloud lines were observed near the dryline, the dryline itself did not initiate any storms over the intensive observation region (IOR). Possible reasons for this lack of convection are discussed. Strong capping inversion and moisture detrainment between the lifting condensation level and the level of free convection related to an overriding drier air, together with the relatively small near-surface moisture values (less than 10 g kg−1), were detrimental to CI in this case.

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