Sounding-Based Thermodynamic Budgets for DYNAMO

2015 ◽  
Vol 72 (2) ◽  
pp. 598-622 ◽  
Author(s):  
Richard H. Johnson ◽  
Paul E. Ciesielski ◽  
James H. Ruppert ◽  
Masaki Katsumata
Keyword(s):  
Radiative Forcing ◽  
Deep Convection ◽  
Active Phase ◽  
Life Cycles ◽  
Radiative Heating ◽  
Convective Heating ◽  
Madden Julian Oscillation ◽  
Heating Rates ◽  
Gross Moist Stability ◽  
Cumulus Congestus

Abstract The Dynamics of the Madden–Julian Oscillation (DYNAMO) field campaign, conducted over the Indian Ocean from October 2011 to March 2012, was designed to study the initiation of the Madden–Julian oscillation (MJO). Two prominent MJOs occurred in the experimental domain during the special observing period in October and November. Data from a northern and a southern sounding array (NSA and SSA, respectively) have been used to investigate the apparent heat sources and sinks (Q1 and Q2) and radiative heating rates QR throughout the life cycles of the two MJO events. The MJO signal was far stronger in the NSA than the SSA. Time series of Q1, Q2, and the vertical eddy flux of moist static energy reveal an evolution of cloud systems for both MJOs consistent with prior studies: shallow, nonprecipitating cumulus during the suppressed phase, followed by cumulus congestus, then deep convection during the active phase, and finally stratiform precipitation. However, the duration of these phases was shorter for the November MJO than for the October event. The profiles of Q1 and Q2 for the two arrays indicate a greater stratiform rain fraction for the NSA than the SSA—a finding supported by TRMM measurements. Surface rainfall rates and net tropospheric QR determined as residuals from the budgets show good agreement with satellite-based estimates. The cloud radiative forcing was approximately 20% of the column-integrated convective heating and of the same amplitude as the normalized gross moist stability, leaving open the possibility of radiative–convective instability for the two MJOs.

Effect of Surface Fluxes versus Radiative Heating on Tropical Deep Convection

2015 ◽  
Vol 72 (9) ◽  
pp. 3378-3388 ◽  
Author(s):  
Usama Anber ◽  
Shuguang Wang ◽  
Adam Sobel
Keyword(s):  
Large Scale ◽  
Multiple Equilibria ◽  
Initial Conditions ◽  
Deep Convection ◽  
Surface Fluxes ◽  
Radiative Heating ◽  
Net Energy ◽  
Wide Range ◽  
Tropical Deep Convection ◽  
Gross Moist Stability

Abstract The effects of turbulent surface fluxes and radiative heating on tropical deep convection are compared in a series of idealized cloud-system-resolving simulations with parameterized large-scale dynamics. Two methods of parameterizing the large-scale dynamics are used: the weak temperature gradient (WTG) approximation and the damped gravity wave (DGW) method. Both surface fluxes and radiative heating are specified, with radiative heating taken as constant in the vertical in the troposphere. All simulations are run to statistical equilibrium. In the precipitating equilibria, which result from sufficiently moist initial conditions, an increment in surface fluxes produces more precipitation than an equal increment of column-integrated radiative heating. This is straightforwardly understood in terms of the column-integrated moist static energy budget with constant normalized gross moist stability. Under both large-scale parameterizations, the gross moist stability does in fact remain close to constant over a wide range of forcings, and the small variations that occur are similar for equal increments of surface flux and radiative heating. With completely dry initial conditions, the WTG simulations exhibit hysteresis, maintaining a dry state with no precipitation for a wide range of net energy inputs to the atmospheric column. The same boundary conditions and forcings admit a rainy state also (for moist initial conditions), and thus multiple equilibria exist under WTG. When the net forcing (surface fluxes minus radiative heating) is increased enough that simulations that begin dry eventually develop precipitation, the dry state persists longer after initialization when the surface fluxes are increased than when radiative heating is increased. The DGW method, however, shows no multiple equilibria in any of the simulations.

Aerosol influences on radiative heating rates in the Asian tropopause aerosol layer

2021 ◽  
Author(s):  
Jie Gao ◽  
Jonathon Wright
Keyword(s):  
Radiative Transfer ◽  
Radiative Forcing ◽  
Asian Monsoon ◽  
Volcanic Eruptions ◽  
Radiative Heating ◽  
Spatiotemporal Variability ◽  
Radiation Budget ◽  
Aerosol Layer ◽  
Heating Rates ◽  
Aerosol Analysis

<p>The Asian Tropopause Aerosol Layer (ATAL) has emerged over recent decades to play an increasingly prominent role in the upper troposphere and lower stratosphere above the Asian monsoon region. Although the effects of the ATAL on the surface and top-of-atmosphere radiation budget have been examined by several studies, the processes and effects by which the ATAL alters radiative transfer within the tropopause layer have been much less discussed. We have used a conditional composite approach to investigate aerosol mixing ratios and their impacts on radiative heating rates in the Asian monsoon tropopause layer in MERRA-2. We have then subsampled in time based on known volcanic eruptions and the evolution of emission and data assimilation inputs to the MERRA-2 aerosol analysis to isolate the ATAL contribution and compare it to radiative heating signatures in the monsoon anticyclone region after volcanic eruptions. The results indicate that the ATAL impact on radiative heating rates in this region is on the order of 0.1 K/day, similar to that associated with ozone variability in MERRA-2 but weaker than cloud radiative effects at these altitudes. We have validated these results and tested their sensitivity to variations in the vertical structure and composition of ATAL aerosols using offline radiative transfer simulations. The idealized simulations produce similar but slightly stronger responses of radiative heating rates to the ATAL and are in good agreement with previous estimates of the top-of-atmosphere radiative forcing. Although the ATAL perturbations inferred from MERRA-2 are only about 10% of mean heating rates at these levels, their spatial distribution suggests potential implications for both isentropic and diabatic transport within the monsoon anticyclone, which should be examined in future work. Our results are limited by uncertainties in the composition and spatiotemporal variability of the ATAL, and reflect only the conditions in this layer as represented by MERRA-2. Targeted observations and model simulations are needed to adequately constrain the uncertainties, particularly with respect to the relative proportions and contributions of nitrate aerosols, which are not included in the MERRA-2 aerosol analysis.</p>

scholarly journals Moist Thermodynamics of the Madden–Julian Oscillation in a Cloud-Resolving Simulation

2011 ◽  
Vol 24 (21) ◽  
pp. 5571-5583 ◽  
Author(s):  
Samson Hagos ◽  
L. Ruby Leung
Keyword(s):  
Time Scales ◽  
Time Scale ◽  
Deep Convection ◽  
Lower Troposphere ◽  
Active Phase ◽  
Vertical Transport ◽  
Madden Julian Oscillation ◽  
Boundary Layer Diffusion ◽  
Inactive Phase ◽  
Thermodynamic Processes

Abstract The moist thermodynamic processes that determine the time scale and energy of the Madden–Julian oscillation (MJO) are investigated using moisture and eddy available potential energy budget analyses on a cloud-resolving simulation. Two MJO episodes observed during the winter of 2007/08 are realistically simulated. During the inactive phase, moisture supplied by meridional moisture convergence and boundary layer diffusion generates shallow and congestus clouds that moisten the lower troposphere while horizontal mixing tends to dry it. As the lower troposphere is moistened, it becomes a source of moisture for the subsequent deep convection during the MJO active phase. As the active phase ends, the lower troposphere dries out primarily by condensation and horizontal divergence that dominates over the moisture supply by vertical transport. In the simulation, the characteristic time scales of convective vertical transport, mixing, and condensation of moisture in the midtroposphere are estimated to be about 2 days, 4 days, and 20 h respectively. The small differences among these time scales result in an effective time scale of MJO moistening of about 25 days, half the period of the simulated MJO. Furthermore, various cloud types have a destabilizing or damping effect on the amplitude of MJO temperature signals, depending on their characteristic latent heating profile and its temporal covariance with the temperature. The results are used to identify possible sources of the difficulties in simulating MJO in low-resolution models that rely on cumulus parameterizations.

Measurements of convective and radiative heating in wildland fires

2013 ◽  
Vol 22 (2) ◽  
pp. 157 ◽  
Author(s):  
David Frankman ◽  
Brent W. Webb ◽  
Bret W. Butler ◽  
Daniel Jimenez ◽  
Jason M. Forthofer ◽  
...  
Keyword(s):  
Fast Response ◽  
Radiative Heating ◽  
Radiative Energy ◽  
Convective Heating ◽  
Wildland Fires ◽  
Ambient Conditions ◽  
Heating Rates ◽  
Total Energy Release ◽  
Time Resolved ◽  
Relative Contribution

Time-resolved irradiance and convective heating and cooling of fast-response thermopile sensors were measured in 13 natural and prescribed wildland fires under a variety of fuel and ambient conditions. It was shown that a sensor exposed to the fire environment was subject to rapid fluctuations of convective transfer whereas irradiance measured by a windowed sensor was much less variable in time, increasing nearly monotonically with the approach of the flame front and largely declining with its passage. Irradiance beneath two crown fires peaked at 200 and 300 kW m–2, peak irradiance associated with fires in surface fuels reached 100 kW m–2 and the peak for three instances of burning in shrub fuels was 132 kW m–2. The fire radiative energy accounted for 79% of the variance in fuel consumption. Convective heating at the sensor surface varied from 15% to values exceeding the radiative flux. Detailed measurements of convective and radiative heating rates in wildland fires are presented. Results indicate that the relative contribution of each to total energy release is dependent on fuel and environment.

scholarly journals Characteristics Associated with the Madden–Julian Oscillation at Manus Island

2013 ◽  
Vol 26 (10) ◽  
pp. 3342-3356 ◽  
Author(s):  
Liping Deng ◽  
Sally A. McFarlane ◽  
Julia E. Flaherty
Keyword(s):  
Phase Structure ◽  
Deep Convection ◽  
Precipitable Water ◽  
Active Phase ◽  
Type I ◽  
Madden Julian Oscillation ◽  
Two Phase ◽  
Easterly Wind ◽  
Mature Phase ◽  
Peak Structure

Abstract Ground-based high temporal and vertical resolution datasets from observations during 2002–07 at the Atmospheric Radiation Measurement (ARM) tropical western Pacific (TWP) site on Manus Island are used to examine the characteristics of clouds and rainfall associated with the active phase of the Madden–Julian oscillation (MJO) passing over Manus. A composite MJO event at Manus is developed based on the NOAA MJO index 4 and precipitation using 13 events. The cloud characteristics associated with the active phase of the MJO at Manus show a two-phase structure as the wave passes over Manus. During the development phase, congestus plays an important role, and the enhanced convection is located between surface westerly and easterly wind anomalies (type-I structure). During the mature phase, deep convection is the dominant cloud type, and the enhanced convection is collocated with the westerly wind anomalies (type-II structure). Consistent with this two-phase structure, the heavy rainfall frequency also shows a two-peak structure during the MJO disturbance, while light rainfall does not show a clear relation to the intraseasonal disturbance associated with the MJO. In addition, a positive relationship between the precipitation rate and precipitable water vapor exists at Manus, and the atmospheric column is less moist after the passing of the MJO convection center than before.

The effect of sampling rate on interpretation of the temporal characteristics of radiative and convective heating in wildland flames

2013 ◽  
Vol 22 (2) ◽  
pp. 168 ◽  
Author(s):  
David Frankman ◽  
Brent W. Webb ◽  
Bret W. Butler ◽  
Daniel Jimenez ◽  
Michael Harrington
Keyword(s):  
Sampling Rate ◽  
Sampling Frequency ◽  
Heat Fluxes ◽  
Radiative Heating ◽  
Convective Heating ◽  
Moving Window ◽  
Prescribed Burn ◽  
Heating Rates ◽  
Time Resolved ◽  
The Difference

Time-resolved radiative and convective heating measurements were collected on a prescribed burn in coniferous fuels at a sampling frequency of 500 Hz. Evaluation of the data in the time and frequency domain indicate that this sampling rate was sufficient to capture the temporal fluctuations of radiative and convective heating. The convective heating signal contained significantly larger fluctuations in magnitude and frequency than did the radiative heating signal. The data were artificially down-sampled to 100, 50, 10, 5 and 1 Hz to explore the effect of sampling rate on peak heat fluxes, time-averaged heating and integrated heating. Results show that for sampling rates less than 5 Hz the difference between measured and actual peak radiative heating rates can be as great as 24%, and is on the order of 80% for 1-Hz sampling rates. Convective heating showed degradation in the signal for sampling rates less than 100 Hz. Heating rates averaged over a 2-s moving window, as well as integrated radiative and convective heating were insensitive to sampling rate across all ranges explored. The data suggest that peak radiative and convective heating magnitudes cannot be fully temporally resolved for sampling frequencies lower than 20 and 200 Hz.

scholarly journals Local Balance and Variability of Atmospheric Heat Budget over Oceans: Observation and Reanalysis-Based Estimates

2014 ◽  
Vol 27 (2) ◽  
pp. 893-913 ◽  
Author(s):  
Sun Wong ◽  
Tristan S. L’Ecuyer ◽  
William S. Olson ◽  
Xianan Jiang ◽  
Eric J. Fetzer
Keyword(s):  
Heat Budget ◽  
Deep Convection ◽  
Tropical Rainfall Measuring Mission ◽  
Heat Fluxes ◽  
Radiative Heating ◽  
Latent Heating ◽  
Heating Rates ◽  
Cooling Rates ◽  
Atmospheric Heating ◽  
Atmospheric Heat

Abstract The authors quantify systematic differences between modern observation- and reanalysis-based estimates of atmospheric heating rates and identify dominant variability modes over tropical oceans. Convergence of heat fluxes between the top of the atmosphere and the surface are calculated over the oceans using satellite-based radiative and sensible heat fluxes and latent heating from precipitation estimates. The convergence is then compared with column-integrated atmospheric heating based on Tropical Rainfall Measuring Mission data as well as the heating calculated using temperatures from the Atmospheric Infrared Sounder and wind fields from the Modern-Era Retrospective Analysis for Research and Applications (MERRA). Corresponding calculations using MERRA and the European Centre for Medium-Range Weather Forecasts Interim Re-Analysis heating rates and heat fluxes are also performed. The geographical patterns of atmospheric heating rates show heating regimes over the intertropical convergence zone and summertime monsoons and cooling regimes over subsidence areas in the subtropical oceans. Compared to observation-based datasets, the reanalyses have larger atmospheric heating rates in heating regimes and smaller cooling rates in cooling regimes. For the averaged heating rates over the oceans in 40°S–40°N, the observation-based datasets have net atmospheric cooling rates (from −15 to −22 W m−2) compared to the reanalyses net warming rates (5.0–5.2 W m−2). This discrepancy implies different pictures of atmospheric heat transport. Wavelet spectra of atmospheric heating rates show distinct maxima of variability in annual, semiannual, and/or intraseasonal time scales. In regimes where deep convection frequently occurs, variability is mainly driven by latent heating. In the subtropical subsidence areas, variability in radiative heating is comparable to that in latent heating.

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 Utilizing a Storm-Generating Hotspot to Study Convective Cloud Transitions: The CACTI Experiment

2021 ◽  
pp. 1-67
Author(s):  
Adam C. Varble ◽  
Stephen W. Nesbitt ◽  
Paola Salio ◽  
Joseph C. Hardin ◽  
Nitin Bharadwaj ◽  
...  
Keyword(s):  
Deep Convection ◽  
Convective Cloud ◽  
Life Cycles ◽  
Field Campaign ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Atmospheric Radiation Measurement ◽  
Cumulus Congestus ◽  
Orographic Cloud ◽  
Convection Initiation

AbstractThe Cloud, Aerosol, and Complex Terrain Interactions (CACTI) field campaign was designed to improve understanding of orographic cloud life cycles in relation to surrounding atmospheric thermodynamic, flow, and aerosol conditions. The deployment to the Sierras de Córdoba range in north-central Argentina was chosen because of very frequent cumulus congestus, deep convection initiation, and mesoscale convective organization uniquely observable from a fixed site. The C-band Scanning Atmospheric Radiation Measurement (ARM) Precipitation Radar was deployed for the first time with over 50 ARM Mobile Facility atmospheric state, surface, aerosol, radiation, cloud, and precipitation instruments between October 2018 and April 2019. An intensive observing period (IOP) coincident with the RELAMPAGO field campaign was held between 1 November and 15 December during which 22 flights were performed by the ARM Gulfstream-1 aircraft.A multitude of atmospheric processes and cloud conditions were observed over the 7-month campaign, including: numerous orographic cumulus and stratocumulus events; new particle formation and growth producing high aerosol concentrations; drizzle formation in fog and shallow liquid clouds; very low aerosol conditions following wet deposition in heavy rainfall; initiation of ice in congestus clouds across a range of temperatures; extreme deep convection reaching 21-km altitudes; and organization of intense, hail-containing supercells and mesoscale convective systems. These comprehensive datasets include many of the first ever collected in this region and provide new opportunities to study orographic cloud evolution and interactions with meteorological conditions, aerosols, surface conditions, and radiation in mountainous terrain.

scholarly journals Impacts of Idealized Air–Sea Coupling on Madden–Julian Oscillation Structure in the Superparameterized CAM

2011 ◽  
Vol 68 (9) ◽  
pp. 1990-2008 ◽  
Author(s):  
James J. Benedict ◽  
David A. Randall
Keyword(s):  
Deep Convection ◽  
Ocean Model ◽  
Surface Fluxes ◽  
Convective Heating ◽  
Madden Julian Oscillation ◽  
Kelvin Wave ◽  
Coupled Simulation ◽  
Wave Response ◽  
Community Atmosphere Model ◽  
Anomalous Surface

Abstract Air–sea interactions and their impact on intraseasonal convective organization are investigated by comparing two 5-yr simulations from the superparameterized Community Atmosphere Model version 3.0 (SP-CAM). The first is forced using prescribed sea surface temperatures (SSTs). The second is identical except that a simplified oceanic mixed-layer model is used to predict tropical SST anomalies that are coupled to the atmosphere. This partially coupled simulation allows SSTs to respond to anomalous surface fluxes. Implementation of the idealized slab ocean model in the SP-CAM results in significant changes to intraseasonal convective variability and organization. The more realistic treatment of air–sea interactions in the coupled simulation improves many aspects of tropical convection on intraseasonal scales, from the relationships between precipitation and SSTs to the space–time structure and propagation of the Madden–Julian oscillation (MJO). This improvement is associated with a more realistic convergence structure and longitudinal gradient of SST relative to MJO deep convection. In the uncoupled SP-CAM, SST is roughly in phase with the MJO convective center and the development of the Kelvin wave response and boundary layer convergence east of the convective center is relatively weak. In the coupled SP-CAM, maxima in SST lead maxima in MJO convection by cycle. Coupling produces warmer SSTs, a stronger Kelvin wave response, enhanced low-level convergence, and increased convective heating ahead (east) of the MJO convective center. Convective development east of the MJO precipitation center is more favorable in the coupled versus the uncoupled version, resulting in more realistic organization and clearer eastward propagation of the MJO in the coupled SP-CAM.

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