scholarly journals 3D radiative heating of tropical upper tropospheric cloud systems derived from synergistic A-Train observations and machine learning

2021 ◽  
Vol 21 (2) ◽  
pp. 1015-1034
Author(s):  
Claudia J. Stubenrauch ◽  
Giacomo Caria ◽  
Sofia E. Protopapadaki ◽  
Friederike Hemmer
Keyword(s):  
Machine Learning ◽  
Radiative Heating ◽  
Convective System ◽  
Heating Rates ◽  
Middle Troposphere ◽  
Surface Warming ◽  
Cloud Systems ◽  
Low Level ◽  
Convective Systems ◽  
Clear Sky

Abstract. Upper tropospheric (UT) cloud systems constructed from Atmospheric Infrared Sounder (AIRS) cloud data provide a horizontal emissivity structure, allowing the convective core to be linked to anvil properties. By using machine learning techniques, we composed a horizontally complete picture of the radiative heating rates deduced from CALIPSO lidar and CloudSat radar measurements, which are only available along narrow nadir tracks. To train the artificial neural networks, we combined the simultaneous AIRS, CALIPSO and CloudSat data with ERA-Interim meteorological reanalysis data in the tropics over a period of 4 years. The resulting non-linear regression models estimate the radiative heating rates as a function of about 40 cloud, atmospheric and surface properties, with a column-integrated mean absolute error (MAE) of 0.8 K d−1 (0.5 K d−1) for cloudy scenes and 0.4 K d−1 (0.3 K d−1) for clear sky in the longwave (shortwave) spectral domain. Developing separate models for (i) high opaque clouds, (ii) cirrus, (iii) mid- and low-level clouds and (iv) clear sky, independently over ocean and over land, leads to a small improvement, when considering the profiles. These models were applied to the whole AIRS cloud dataset, combined with ERA-Interim, to build 3D radiative heating rate fields. Over the deep tropics, UT clouds have a net radiative heating effect of about 0.3 K d−1 throughout the troposphere from 250 hPa downward. This radiative heating enhances the column-integrated latent heating by about 22±3 %. While in warmer regions the net radiative heating profile is nearly completely driven by deep convective cloud systems, it is also influenced by low-level clouds in the cooler regions. The heating rates of the convective systems in both regions also differ: in the warm regions the net radiative heating by the thicker cirrus anvils is vertically more extended, and their surrounding thin cirrus heat the entire troposphere by about 0.5 K d−1. The 15-year time series reveal a slight increase of the vertical heating in the upper and middle troposphere by convective systems with tropical surface temperature warming, which can be linked to deeper systems. In addition, the layer near the tropopause is slightly more heated by increased thin cirrus during periods of surface warming. While the relative coverage of convective systems is relatively stable with surface warming, their depth increases, measured by a decrease of their near-top temperature of -3.4±0.2 K K−1. Finally, the data reveal a connection of the mesoscale convective system (MCS) heating in the upper and middle troposphere and the (low-level) cloud cooling in the lower atmosphere in the cool regions, with a correlation coefficient equal to 0.72, which consolidates the hypothesis of an energetic connection between the convective regions and the subsidence regions.

scholarly journals 3D Radiative Heating of Tropical Upper Tropospheric Cloud Systems derived from Synergistic A-Train Observations and Machine Learning

2020 ◽  
Author(s):  
Claudia J. Stubenrauch ◽  
Giacomo Caria ◽  
Sofia E. Protopapadaki ◽  
Friederike Hemmer
Keyword(s):  
Machine Learning ◽  
Radiative Heating ◽  
Machine Learning Techniques ◽  
Linear Regression Models ◽  
Heating Rates ◽  
Cloud Systems ◽  
Low Level ◽  
Clear Sky ◽  
Convective Core ◽  
Cooling Effects

Abstract. Upper Tropospheric (UT) cloud systems constructed from Atmospheric Infrared Sounder (AIRS) cloud data provide a horizontal emissivity structure, allowing to link convective core to anvil properties. By using machine learning techniques we composed a horizontally complete picture of the radiative heating rates deduced from CALIPSO lidar and CloudSat radar measurements, which are only available along narrow nadir tracks. To train the artificial neural networks, we combined the simultaneous AIRS, CALIPSO and CloudSat data with ERA-Interim meteorological reanalysis data in the tropics over a period of four years. Resulting non-linear regression models estimate the radiative heating rates as a function of about 40 cloud, atmospheric and surface properties, with a column-integrated mean absolute error (MAE) of 0.8 K/d (0.5 K/day) for cloudy scenes and 0.4 (0.3 K/day) for clear sky in the longwave (shortwave) spectral domain. Already about 20 basic input variables yield good results, with a 6 % (10 %) larger MAE. Developing separate models for (i) high opaque clouds, (ii) cirrus, (iii) mid- and low-level clouds and (iv) clear sky, independently over ocean and over land, lead to a small improvement, when considering the profile shapes. These models were then applied to the whole AIRS cloud dataset, combined with ERA-Interim, to build 3D radiative heating rate fields. Over the deep tropics, UT clouds have a net radiative heating effect of about 0.3 K/day throughout the troposphere from 250 hPa downward, with a broad maximum of about 0.4 K/d around 330 hPa, enhancing the column-integrated latent heating by about 25 %. This value is larger than earlier results of about 20 %. Above the height of 200 hPa, the LW cooling above convective cores and thick cirrus anvils is opposed by thin cirrus heating. Whereas in cooler regions low-level clouds also influence the net radiative heating profile, in warmer regions it is nearly completely driven by deep convective cloud systems. These mesoscale convective systems (MCS) are colder and include slightly more thin cirrus around their anvils than those in cooler regions. Hence, the MCSs over these warmer regions produce a vertically more extended heating by the thicker cirrus anvils and a heating of 0.7 K/d above the height of 200 hPa by the surrounding thin cirrus. The roughly estimated horizontal gradients between cirrus anvil and convective core as well as between surrounding thin cirrus and cirrus anvil seem to be slightly smaller in warmer regions, which can be explained by their larger coverage. The 15-year time series of the heating/cooling effects of MCSs are well related to the ENSO variation. While the coverage of all MCSs is relatively stable (or very slightly decreasing) with surface warming, with −1.3 ± 0.6 %/K, the coverage of cold MCSs relative to all MCSs significantly increases by +18 ± 5 %/K.

Impact of Environmental Variations on Simulated Squall Lines Interacting with Terrain

2011 ◽  
Vol 139 (10) ◽  
pp. 3163-3183 ◽  
Author(s):  
Casey E. Letkewicz ◽  
Matthew D. Parker
Keyword(s):  
Wind Profile ◽  
Windward Side ◽  
Squall Line ◽  
Cold Pool ◽  
Convective System ◽  
Low Level ◽  
Convective Systems ◽  
Squall Lines ◽  
Strong Convection ◽  
The Mean

Abstract The complex evolution of convective systems crossing (or attempting to cross) mountainous terrain represents a substantial forecasting challenge. This study examines the processes associated with environments of “crossing” squall lines (which were able to redevelop strong convection in the lee of a mountain barrier) and “noncrossing” squall lines (which were not able to redevelop strong convection downstream of the barrier). In particular, numerical simulations of mature convective systems crossing idealized terrain roughly approximating the Appalachian Mountains were used to test the first-order impact of variations in the vertical wind profile upon system maintenance. By itself, the wind profile showed no ability to uniquely discriminate between simulated crossing and noncrossing squall lines; each test revealed a similar pattern of orographic enhancement, suppression, and lee reinvigoration in which a hydraulic jump deepened the system’s cold pool and renewed the low-level lifting. Increasing the mean wind led to greater enhancement of vertical velocities on the windward side of the barrier and greater suppression on the lee side. Variations in the low-level shear influenced the temperature and depth of the outflow, which in turn altered the lifting along the system’s gust front. However, in all of the wind profile tests, convection redeveloped in the lee. Additional simulations explored more marginal environments in which idealized low-level cooling or drying stabilized the downstream environment. In most such tests, the systems weakened but the presence of CAPE aloft still enabled the systems to survive in the lee. However, the combination of a stronger mean wind with diminished CAPE and increased convective inhibition (CIN) was ultimately found to eliminate downstream redevelopment and produce a noncrossing mesoscale convective system (MCS). Within these experiments, the ability of a squall line to cross a barrier similar to the Appalachians is primarily tied to the characteristics of the downstream thermodynamic environment; however, as the lee thermodynamic environment becomes less favorable, the mean wind exerts a greater influence on system intensity and redevelopment.

Controls of Quasi-linear Convective System Tornado Intensity

2021 ◽  
Author(s):  
Geoffrey R. Marion ◽  
Robert J. Trapp
Keyword(s):  
Negative Impact ◽  
Cold Pool ◽  
Convective System ◽  
Cool Season ◽  
Initiation Mechanism ◽  
Direct Role ◽  
Near Surface ◽  
Low Level ◽  
Convective Systems ◽  
Short Time

AbstractAlthough tornadoes produced by quasi-linear convective systems (QLCSs) generally are weak and short-lived, they have high societal impact due to their proclivity to develop over short time scales, within the cool season, and during nighttime hours. Precisely why they are weak and short lived is not well understood, although recent work suggests that QLCS updraft width may act as a limitation to tornado intensity. Herein, idealized simulations of tornadic QLCSs are performed with variations in hodograph shape and length as well as initiation mechanism to determine the controls of tornado intensity. Generally, the addition of hodograph curvature in these experiments results in stronger, longer-lived tornadic like vortices (TLVs). A strong correlation between low-level mesocyclone width and TLV intensity is identified (R2 = 0.61), with a weaker correlation in the low-level updraft intensity (R2 = 0.41). The tilt and depth of the updraft are found to have little correlation to tornado intensity. Comparing QLCS and isolated supercell updrafts within these simulations, the QLCS updrafts are less persistent, with the standard deviations of low-level vertical velocity and updraft helicity to be approximately 48% and 117% greater, respectively. A forcing decomposition reveals that the QLCS cold pool plays a direct role in the development of the low-level updraft, providing the benefit of additional forcing for ascent while also having potentially deleterious effects on both the low-level updraft and near-surface rotation. The negative impact of the cold pool ultimately serves to limit the persistence of rotating updraft cores within the QLCS.

scholarly journals Sensitivity of Precipitation Accumulation in Elevated Convective Systems to Small Changes in Low-Level Moisture

2015 ◽  
Vol 72 (6) ◽  
pp. 2507-2524 ◽  
Author(s):  
Russ S. Schumacher
Keyword(s):  
Surface Layer ◽  
Convective Available Potential Energy ◽  
Mesoscale Convective System ◽  
Extreme Rainfall ◽  
Heavy Rain ◽  
Convective System ◽  
Modeling Framework ◽  
Near Surface ◽  
Low Level ◽  
Convective Systems

Abstract Using a method for initiating a quasi-stationary, heavy-rain-producing elevated mesoscale convective system in an idealized numerical modeling framework, a series of experiments is conducted in which a shallow layer of drier air is introduced within the near-surface stable layer. The environment is still very moist in the experiments, with changes to the column-integrated water vapor of only 0.3%–1%. The timing and general evolution of the simulated convective systems are very similar, but rainfall accumulation at the surface is changed by a much larger fraction than the reduction in moisture, with point precipitation maxima reduced by up to 29% and domain-averaged precipitation accumulations reduced by up to 15%. The differences in precipitation are partially attributed to increases in the evaporation rate in the shallow subcloud layer, though this is found to be a secondary effect. More importantly, even though the near-surface layer has strong convective inhibition in all simulations and the convective available potential energy of the most unstable parcels is unchanged, convection is less intense in the experiments with drier subcloud layers because less air originating in that layer rises in convective updrafts. An additional experiment with a cooler near-surface layer corroborates these findings. The results from these experiments suggest that convective systems assumed to be elevated are, in fact, drawing air from near the surface unless the low levels are very stable. Considering that the moisture differences imposed here are comparable to observational uncertainties in low-level temperature and moisture, the strong sensitivity of accumulated precipitation to these quantities has implications for the predictability of extreme rainfall.

Views on Applying RKW Theory: An Illustration Using the 8 May 2009 Derecho-Producing Convective System

2012 ◽  
Vol 140 (3) ◽  
pp. 1023-1043 ◽  
Author(s):  
Michael C. Coniglio ◽  
Stephen F. Corfidi ◽  
John S. Kain
Keyword(s):  
Normal Component ◽  
Vertical Wind Shear ◽  
Companion Paper ◽  
System Structure ◽  
Cold Pool ◽  
Convective System ◽  
Near Surface ◽  
Low Level ◽  
Convective Systems ◽  
Shear Component

Abstract This work presents an analysis of the vertical wind shear during the early stages of the remarkable 8 May 2009 central U.S. derecho-producing convective system. Comments on applying Rotunno–Klemp–Weisman (RKW) theory to mesoscale convective systems (MCSs) of this type also are provided. During the formative stages of the MCS, the near-surface-based shear vectors ahead of the leading convective line varied with time, location, and depth, but the line-normal component of the shear in any layer below 3 km ahead of where the strong bow echo developed was relatively small (6–9 m s−1). Concurrently, the midlevel (3–6 km) line-normal shear component had magnitudes mostly >10 m s−1 throughout. In a previous companion paper, it was hypothesized that an unusually strong and expansive low-level jet led to dramatic changes in instability, shear, and forced ascent over mesoscale areas. These mesoscale effects may have overwhelmed the interactions between the cold pool and low-level shear that modulate system structure in less complex environments. If cold pool–shear interactions were critical to producing such a strong system, then the extension of the line-normal shear above 3 km also appeared to be critical. It is suggested that RKW theory be applied with much caution, and that examining the shear above 3 km is important, if one wishes to explain the formation and maintenance of intense long-lived convective systems, particularly complex nocturnal systems like the one that occurred on 8 May 2009.

scholarly journals A Numerical Simulation Study of the Effects of Anvil Shading on Quasi-Linear Convective Systems

2013 ◽  
Vol 70 (3) ◽  
pp. 767-793 ◽  
Author(s):  
Andrew J. Oberthaler ◽  
Paul M. Markowski
Keyword(s):  
Solar Radiation ◽  
Wind Shear ◽  
Wind Profile ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Convective System ◽  
Near Surface ◽  
Low Level ◽  
Convective Systems ◽  
Gust Front

Abstract Numerical simulations are used to investigate how the attenuation of solar radiation by the intervening cumulonimbus cloud, particularly its large anvil, affects the structure, intensity, and evolution of quasi-linear convective systems and the sensitivity of the effects of this “anvil shading” to the ambient wind profile. Shading of the pre-gust-front inflow environment (as opposed to shading of the cold pool) has the most important impact on the convective systems. The magnitude of the low-level cooling, associated baroclinicity, and stabilization of the pre-gust-front environment due to anvil shading generally increases as the duration of the shading increases. Thus, for a given leading anvil length, a slow-moving convective system tends to be affected more by anvil shading than does a fast-moving convective system. Differences in the forward speeds of the convective systems simulated in this study are largely attributable to differences in the mean environmental wind speed over the depth of the troposphere. Anvil shading reduces the buoyancy realized by the air parcels that ascend through the updrafts. As a result, anvil shading contributes to weaker updrafts relative to control simulations in which clouds are transparent to solar radiation. Anvil shading also affects the convective systems by modifying the low-level (nominally 0–2.5 km AGL) vertical wind shear in the pre-gust-front environment. The shear modifications affect the slope of the updraft region and system-relative rear-to-front flow, and the sign of the modifications is sensitive to the ground-relative vertical wind profile in the far-field environment. The vertical wind shear changes are brought about by baroclinic vorticity generation associated with the horizontal buoyancy gradient that develops in the shaded boundary layer (which makes the pre-gust-front, low-level vertical wind shear less westerly) and by a reduction of the vertical mixing of momentum due to the near-surface (nominally 0–300 m AGL) stabilization that accompanies the shading-induced cooling. The reduced mixing makes the pre-gust-front, low-level vertical shear more (less) westerly if the ambient, near-surface wind and wind shear are westerly (easterly).

The Amazonian Low-Level Jet and Its Connection to Convective Cloud Propagation and Evolution

2020 ◽  
Vol 148 (10) ◽  
pp. 4083-4099 ◽  
Author(s):  
Evandro M. Anselmo ◽  
Courtney Schumacher ◽  
Luiz A. T. Machado
Keyword(s):  
Convective Cloud ◽  
Moisture Flux ◽  
Time Of Day ◽  
Convective System ◽  
South American ◽  
Low Level ◽  
Convective Systems ◽  
Wind Speeds ◽  
Cloud Clusters ◽  
Low Level Jet

AbstractWe describe the existence of an Amazonian low-level jet (ALLJ) that can affect the propagation and life cycle of convective systems from the northeast coast of South America into central Amazonia. Horizontal winds from reanalysis were analyzed during March–April–May (MAM) of the two years (2014–15) of the GoAmazon2014/5 field campaign. Convective system tracking was performed using GOES-13 infrared imagery and classified into days with high and weak convective activity. The MAM average winds show a nocturnal enhancement of low-level winds starting near the coast in the early evening and reaching 1600 km inland by late morning. Mean 3-hourly wind speeds maximize at 9–10 m s−1 near 900 hPa, but individual days can have nighttime low-level winds exceeding 12 m s−1. Based on objective low-level wind criteria, the ALLJ is present 10%–40% of the time over the Amazon during MAM depending on the location and time of day. The evolution of the ALLJ across the Amazon impacts the frequency of occurrence of cloud clusters and the intensity of the moisture flux. In addition, the ALLJ is associated with the enhancement of northeasterly flow in the midtroposphere during active convective days, when vertical momentum transport may be occurring in the organized cloud clusters. During the weakly active convective period, the ALLJ is weaker near the coast but stronger across the central Amazon and appears to be linked more directly with the South American low-level jet.

scholarly journals Major Characteristics of Southern Ocean Cloud Regimes and Their Effects on the Energy Budget

2011 ◽  
Vol 24 (19) ◽  
pp. 5061-5080 ◽  
Author(s):  
John M. Haynes ◽  
Christian Jakob ◽  
William B. Rossow ◽  
George Tselioudis ◽  
Josephine Brown
Keyword(s):  
Southern Ocean ◽  
Large Scale ◽  
Climate Models ◽  
Satellite Observation ◽  
Radiative Heating ◽  
Radiation Balance ◽  
Heating Rates ◽  
Cloud Systems ◽  
Low Cloud ◽  
Cloud Regimes

Clouds over the Southern Ocean are often poorly represented by climate models, but they make a significant contribution to the top-of-atmosphere (TOA) radiation balance, particularly in the shortwave portion of the energy spectrum. This study seeks to better quantify the organization and structure of Southern Hemisphere midlatitude clouds by combining measurements from active and passive satellite-based datasets. Geostationary and polar-orbiter satellite data from the International Satellite Cloud Climatology Project (ISCCP) are used to quantify large-scale, recurring modes of cloudiness, and active observations from CloudSat and Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) are used to examine vertical structure, radiative heating rates, and precipitation associated with these clouds. It is found that cloud systems are organized into eight distinct regimes and that ISCCP overestimates the midlevel cloudiness of these regimes. All regimes contain a relatively high occurrence of low cloud, with 79% of all cloud layers observed having tops below 3 km, but multiple-layered clouds systems are present in approximately 34% of observed cloud profiles. The spatial distribution of regimes varies according to season, with cloud systems being geometrically thicker, on average, during the austral winter. Those regimes found to be most closely associated with midlatitude cyclones produce precipitation the most frequently, although drizzle is extremely common in low-cloud regimes. The regimes associated with cyclones have the highest in-regime shortwave cloud radiative effect at the TOA, but the low-cloud regimes, by virtue of their high frequency of occurrence over the oceans, dominate both TOA and surface shortwave effects in this region as a whole.

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