scholarly journals Climatology and Interannual Variability of Boreal Spring Wet Season Precipitation in the Eastern Horn of Africa and Implications for Its Recent Decline

2017 ◽  
Vol 30 (10) ◽  
pp. 3867-3886 ◽  
Author(s):  
Brant Liebmann ◽  
Ileana Bladé ◽  
Chris Funk ◽  
Dave Allured ◽  
Xiao-Wei Quan ◽  
...  
Keyword(s):  
Heat Source ◽  
Potential Energy ◽  
Interannual Variability ◽  
Convective Available Potential Energy ◽  
Specific Humidity ◽  
Horn Of Africa ◽  
Wet Season ◽  
Important Ingredient ◽  
Low Level ◽  
Boreal Spring

Abstract The 1981–2014 climatology and variability of the March–May eastern Horn of Africa boreal spring wet season are examined using precipitation, upper- and lower-level winds, low-level specific humidity, and convective available potential energy (CAPE), with the aim of better understanding the establishment of the wet season and the cause of the recent observed decline. At 850 mb, the development of the wet season is characterized by increasing specific humidity and winds that veer from northeasterly in February to southerly in June and advect moisture into the region, in agreement with an earlier study. Equally important, however, is a substantial weakening of the 200-mb climatological easterly winds in March. Likewise, the shutdown of the wet season coincides with the return of strong easterly winds in June. Similar changes are seen in the daily evolution of specific humidity and 200-mb wind when composited relative to the interannual wet season onset and end, with the easterlies decreasing (increasing) several days prior to the start (end) of the wet season. The 1981–2014 decrease in March–May precipitation has also coincided with an increase in 200-mb easterly winds, with no attendant change in specific humidity, leading to the conclusion that, while high values of specific humidity are an important ingredient of the wet season, the recent observed precipitation decline has resulted mostly from a strengthening of the 200-mb easterlies. This change in the easterly winds appears to be related to an increase in convection over the Indonesian region and in the associated outflow from that enhanced heat source.

Changes in Convective Available Potential Energy and Convective Inhibition under Global Warming

2020 ◽  
Vol 33 (6) ◽  
pp. 2025-2050 ◽  
Author(s):  
Jiao Chen ◽  
Aiguo Dai ◽  
Yaocun Zhang ◽  
Kristen L. Rasmussen
Keyword(s):  
Global Warming ◽  
Potential Energy ◽  
Climate Model ◽  
Convective Available Potential Energy ◽  
The United States ◽  
Specific Humidity ◽  
Low Level ◽  
Available Potential Energy ◽  
Convective Inhibition ◽  
The Impact

AbstractAtmospheric convective available potential energy (CAPE) is expected to increase under greenhouse gas–induced global warming, but a recent regional study also suggests enhanced convective inhibition (CIN) over land although its cause is not well understood. In this study, a global climate model is first evaluated by comparing its CAPE and CIN with reanalysis data, and then their future changes and the underlying causes are examined. The climate model reasonably captures the present-day CAPE and CIN patterns seen in the reanalysis, and projects increased CAPE almost everywhere and stronger CIN over most land under global warming. Over land, the cases or times with medium to strong CAPE or CIN would increase while cases with weak CAPE or CIN would decrease, leading to an overall strengthening in their mean values. These projected changes are confirmed by convection-permitting 4-km model simulations over the United States. The CAPE increase results mainly from increased low-level specific humidity, which leads to more latent heating and buoyancy for a lifted parcel above the level of free convection (LFC) and also a higher level of neutral buoyancy. The enhanced CIN over most land results mainly from reduced low-level relative humidity (RH), which leads to a higher lifting condensation level and a higher LFC and thus more negative buoyancy. Over tropical oceans, the near-surface RH increases slightly, leading to slight weakening of CIN. Over the subtropical eastern Pacific and Atlantic Ocean, the impact of reduced low-level atmospheric lapse rates overshadows the effect of increased specific humidity, leading to decreased CAPE.

scholarly journals Seeking for key meteorological parameters to better understand Hector

2015 ◽  
Vol 3 (6) ◽  
pp. 3621-3653
Author(s):  
S. Gentile ◽  
R. Ferretti
Keyword(s):  
Potential Energy ◽  
Meteorological Parameters ◽  
Mesoscale Model ◽  
Initial Conditions ◽  
Convective Available Potential Energy ◽  
Surface Wind ◽  
Type A ◽  
Weather Forecasts ◽  
Low Level ◽  
Available Potential Energy

Abstract. Twelve Hector events, a storm developing in the northern Australia, are analyzed to the aim of identifying the main meteorological parameters involved in the convective development. Based on Crook's ideal study \\citep{Crook} wind speed and direction, wind shear, water vapor, Convective Available Potential Energy and type of convection are the parameters used for this analysis. Both European Centre for Medium-Range Weather Forecasts (ECMWF) analysis and high resolution simulations from the Fifth-Generation Mesoscale Model (MM5) are used. The MM5 simulations are used to connect the mean vertical velocity to the total condensate at the maximum stage and to study the dynamics of the storms. The ECMWF analysis are used to evaluate the initial conditions and the environmental fields contributing to Hector development. The analysis suggests that the strength of convection is largely contributing to the vertical distribution of hydrometeors. The role of total condensate and mean lifting vs. low level moisture, Convective Available Potential Energy, surface wind and direction is analyzed for shear and no-shear conditions to evaluate the differences between type A and B for real events. Results confirm the tendency suggested by Crook's analysis. On the other hand, Crook's hypothesis of low level moisture as the only parameter that differentiates between type A and B can be applied only if the events develop in the same meteorological conditions. Crook's tests also helped to asses how the the meteorological parameters contribute to Hector development in terms of percentage.

An Unusual Hailstorm on 24 June 2006 in Boulder, Colorado. Part I: Mesoscale Setting and Radar Features

2008 ◽  
Vol 136 (8) ◽  
pp. 2813-2832 ◽  
Author(s):  
Paul T. Schlatter ◽  
Thomas W. Schlatter ◽  
Charles A. Knight
Keyword(s):  
Boundary Layer ◽  
Potential Energy ◽  
Convective Available Potential Energy ◽  
Meteorological Conditions ◽  
Vertical Shear ◽  
Low Density ◽  
The South ◽  
Low Level ◽  
Available Potential Energy

Abstract An unusual, isolated hailstorm descended on Boulder, Colorado, on the evening of 24 June 2006. Starting with scattered large, flattened, disk-shaped hailstones and ending with a deluge of slushy hail that was over 4 cm deep on the ground, the storm lasted no more than 20 min and did surprisingly little damage except to vegetation. Part I of this two-part paper examines the meteorological conditions preceding the storm and the signatures it exhibited on Weather Surveillance Radar-1988 Doppler (WSR-88D) displays. There was no obvious upper-tropospheric forcing for this storm, vertical shear of the low-level wind was minimal, the boundary layer air feeding the storm was not very moist (maximum dewpoint 8.5°C), and convective available potential energy calculated from a modified air parcel was at most 1550 J kg−1. Despite these handicaps, the hail-producing storm had low-level reflectivity exceeding 70 dBZ, produced copious low-density hail, exhibited strong rotation, and generated three extensive bounded weak-echo regions (BWERs) in succession. The earliest of these filled with high reflectivities as the second one to the south poked up through precipitation-filled air. This has implications for low-density hail growth, as discussed in Part II.

scholarly journals Seeking key meteorological parameters to better understand Hector

2016 ◽  
Vol 16 (2) ◽  
pp. 431-447
Author(s):  
S. Gentile ◽  
R. Ferretti
Keyword(s):  
Potential Energy ◽  
Vertical Velocity ◽  
Meteorological Parameters ◽  
Mesoscale Model ◽  
Initial Conditions ◽  
Convective Available Potential Energy ◽  
Surface Wind ◽  
Type A ◽  
Low Level ◽  
Available Potential Energy

Abstract. Twelve Hector events, a storm which develops in northern Australia, are analyzed with the aim of identifying the main meteorological parameters involved in the storm's convective development. Based on Crook's ideal study (Crook, 2001), wind speed and direction, wind shear, water vapor, convective available potential energy and type of convection are the parameters used for this analysis. Both the European Centre for Medium-Range Weather Forecasts (ECMWF) analysis and high-resolution simulations from the Fifth-Generation Mesoscale Model (MM5) are used. The MM5 simulations are used to connect the mean vertical velocity to the total condensate at the maximum stage and to study the dynamics of the storms. The ECMWF analyses are used to evaluate the initial conditions and the environmental fields contributing to Hector's development. The analysis suggests that the strength of convection, defined in terms of vertical velocity, largely contributes to the vertical distribution of hydrometeors. The role of total condensate and mean lifting versus low-level moisture, convective available potential energy, surface wind and direction is analyzed for shear and no-shear conditions to evaluate the differences between type A and B for real events. Results confirm the tendency suggested by Crook's analysis. However, Crook's hypothesis of low-level moisture as the only parameter that differentiates between type A and B can only be applied if the events develop in the same meteorological conditions. Crook's tests also helped to assess how the meteorological parameters contribute to Hector's development in terms of percentage.

scholarly journals The North Dakota Tornadic Supercells of 18 July 2004: Issues Concerning High LCL Heights and Evapotranspiration

2007 ◽  
Vol 22 (6) ◽  
pp. 1200-1213 ◽  
Author(s):  
David J. Kellenbenz ◽  
Thomas J. Grafenauer ◽  
Jonathan M. Davies
Keyword(s):  
Potential Energy ◽  
North Dakota ◽  
Convective Available Potential Energy ◽  
Low Level ◽  
Surface Moisture ◽  
The North ◽  
Statistical Studies ◽  
Convection Initiation ◽  
Lapse Rates ◽  
Lifting Condensation Level

Abstract On the evening of 18 July 2004, several tornadoes occurred with two supercell thunderstorms over eastern North Dakota. The second and smaller in diameter of these storms produced an F4 tornado in an environment with lifting condensation level (LCL) heights that were atypically high according to recent statistical studies about supercell tornado environments. Surface dewpoints were also underforecast by computer models. These two issues are examined in this paper, which provides an overview of this event. The synoptic setting and environment characteristics suggest that evapotranspiration (ET) was responsible in part for enhancing surface moisture. It is likely that ET affected instability and convection initiation. This study also found that the presence of steep low-level lapse rates juxtaposed with low-level convective available potential energy along a surface trough may have contributed to tornado development in a high LCL environment where wind and instability characteristics were otherwise favorable for supporting supercell tornadoes.

scholarly journals Evaluating the Effective Inflow Layer of Simulated Supercell Updrafts

2020 ◽  
Vol 148 (8) ◽  
pp. 3507-3532 ◽  
Author(s):  
Christopher J. Nowotarski ◽  
John M. Peters ◽  
Jake P. Mulholland
Keyword(s):  
Potential Energy ◽  
Deep Layer ◽  
Dynamic Pressure ◽  
Convective Available Potential Energy ◽  
Severe Weather ◽  
Convective Storms ◽  
Low Level ◽  
Available Potential Energy ◽  
Supercell Thunderstorms ◽  
Relative Flow

Abstract Proper prediction of the inflow layer of deep convective storms is critical for understanding their potential updraft properties and likelihood of producing severe weather. In this study, an existing forecast metric known as the effective inflow layer (EIL) is evaluated with an emphasis on its performance for supercell thunderstorms, where both buoyancy and dynamic pressure accelerations are common. A total of 15 idealized simulations with a range of realistic base states are performed. Using an array of passive fluid tracers initialized at various vertical levels, the proportion of simulated updraft core air originating from the EIL is determined. Results suggest that the EIL metric performs well in forecasting peak updraft origin height, particularly for supercell updrafts. Moreover, the EIL metric displays consistent skill across a range of updraft core definitions. The EIL has a tendency to perform better as convective available potential energy, deep-layer shear, and EIL depth are increased in the near-storm environment. Modifications to further constrain the EIL based on the most-unstable parcel height or storm-relative flow may lead to marginal improvements for the most stringent updraft core definitions. Finally, effects of the near-storm environment on low-level and peak updraft forcing and intensity are discussed.

scholarly journals Tornadoes in Environments with Small Helicity and/or High LCL Heights

2006 ◽  
Vol 21 (4) ◽  
pp. 579-594 ◽  
Author(s):  
Jonathan M. Davies
Keyword(s):  
Empirical Study ◽  
Free Convection ◽  
Potential Energy ◽  
Convective Available Potential Energy ◽  
Thermodynamic Characteristics ◽  
Cycle Model ◽  
Vertical Vorticity ◽  
Low Level ◽  
Convective Inhibition ◽  
Lapse Rates

Abstract Recent studies have suggested that supercell tornado environments are usually associated with large 0–1-km storm-relative helicity (SRH) and relatively low lifting condensation levels (LCL heights). However, occasional tornadoes of significance occur in environments having characteristics that appear less supportive of supercell tornadoes, including small SRH values and/or relatively high LCL heights. Such tornadoes, whether associated with supercell or nonsupercell processes (more precisely termed mesocyclone and nonmesocyclone processes), present a challenge for forecasters. This empirical study uses a database of soundings derived from the Rapid Update Cycle model to examine thermodynamic characteristics of F1 and greater intensity tornado events associated with small SRH and/or high LCL heights. Results strongly suggest that many such tornado events are associated with steep lapse rates in the lowest few kilometers above ground. The low level of free convection heights, small convective inhibition, and sizable convective available potential energy below 3 km were also found to be of possible importance. These thermodynamic characteristics combined would likely reduce resistance to upward accelerations, potentially enhancing ascent for low-level parcels entering thunderstorm updrafts and, hence, low-level stretching. From prior research, if preexisting boundaries were available to provide surface vertical vorticity for stretching, such thermodynamic characteristics could be an important component of tornado events that involve nonmesocyclone processes. These same thermodynamic characteristics may also offer clues for the investigation of mesocyclone tornado events that do not fit well with accepted tornado forecasting parameters from prior studies.

scholarly journals Geographic Shift and Environment Change of U.S. Tornado Activities in a Warming Climate

Atmosphere ◽  
2021 ◽  
Vol 12 (5) ◽  
pp. 567
Author(s):  
Zuohao Cao ◽  
Huaqing Cai ◽  
Guang J. Zhang
Keyword(s):  
Wind Shear ◽  
Convective Available Potential Energy ◽  
Geographic Location ◽  
Reanalysis Data ◽  
Cyclonic Circulation ◽  
Upward Motion ◽  
Environment Change ◽  
Low Level ◽  
High Event ◽  
The U.S

Even with ever-increasing societal interest in tornado activities engendering catastrophes of loss of life and property damage, the long-term change in the geographic location and environment of tornado activity centers over the last six decades (1954–2018), and its relationship with climate warming in the U.S., is still unknown or not robustly proved scientifically. Utilizing discriminant analysis, we show a statistically significant geographic shift of U.S. tornado activity center (i.e., Tornado Alley) under warming conditions, and we identify five major areas of tornado activity in the new Tornado Alley that were not identified previously. By contrasting warm versus cold years, we demonstrate that the shift of relative warm centers is coupled with the shifts in low pressure and tornado activity centers. The warm and moist air carried by low-level flow from the Gulf of Mexico combined with upward motion acts to fuel convection over the tornado activity centers. Employing composite analyses using high resolution reanalysis data, we further demonstrate that high tornado activities in the U.S. are associated with stronger cyclonic circulation and baroclinicity than low tornado activities, and the high tornado activities are coupled with stronger low-level wind shear, stronger upward motion, and higher convective available potential energy (CAPE) than low tornado activities. The composite differences between high-event and low-event years of tornado activity are identified for the first time in terms of wind shear, upward motion, CAPE, cyclonic circulation and baroclinicity, although some of these environmental variables favorable for tornado development have been discussed in previous studies.

scholarly journals Ocean Convective Available Potential Energy. Part II: Energetics of Thermobaric Convection and Thermobaric Cabbeling

2016 ◽  
Vol 46 (4) ◽  
pp. 1097-1115 ◽  
Author(s):  
Zhan Su ◽  
Andrew P. Ingersoll ◽  
Andrew L. Stewart ◽  
Andrew F. Thompson
Keyword(s):  
Potential Energy ◽  
Deep Convection ◽  
Center Of Mass ◽  
Convective Available Potential Energy ◽  
Vertical Mixing ◽  
Available Potential Energy ◽  
Energy Part ◽  
Different Temperatures ◽  
Simplifying Assumptions ◽  
Diabatic Processes

AbstractThe energetics of thermobaricity- and cabbeling-powered deep convection occurring in oceans with cold freshwater overlying warm salty water are investigated here. These quasi-two-layer profiles are widely observed in wintertime polar oceans. The key diagnostic is the ocean convective available potential energy (OCAPE), a concept introduced in a companion piece to this paper (Part I). For an isolated ocean column, OCAPE arises from thermobaricity and is the maximum potential energy (PE) that can be converted into kinetic energy (KE) under adiabatic vertical parcel rearrangements. This study explores the KE budget of convection using two-dimensional numerical simulations and analytical estimates. The authors find that OCAPE is a principal source for KE. However, the complete conversion of OCAPE to KE is inhibited by diabatic processes. Further, this study finds that diabatic processes produce three other distinct contributions to the KE budget: (i) a sink of KE due to the reduction of stratification by vertical mixing, which raises water column’s center of mass and thus acts to convert KE to PE; (ii) a source of KE due to cabbeling-induced shrinking of the water column’s volume when water masses with different temperatures are mixed, which lowers the water column’s center of mass and thus acts to convert PE into KE; and (iii) a reduced production of KE due to diabatic energy conversion of the KE convertible part of the PE to the KE inconvertible part of the PE. Under some simplifying assumptions, the authors also propose a theory to estimate the maximum depth of convection from an energetic perspective. This study provides a potential basis for improving the convection parameterization in ocean models.

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