An Evaluation of CAPE Tendency in Tornado Outbreaks

Previous studies (e.g., Rasmussen, 2003; Thompson et al., 2003) have examined the impact that instability has on the occurrence of tornadic supercells. However, few studies (e.g., Calas et al., 2000) have examined the impact that the rate of destabilization has on the development of severe convection. Utilizing a CAPE tendency equation derived by Emanuel (1994), this study examines the impact of the rate of atmospheric destabilization on the severity of convection. Comparing six hour analyses of CAPE tendency with observed tornado tracks from the 4-6 May 2007, 5-6 February 2008, and 17 June 2010 tornado outbreaks reveals a potential correlation between CAPE tendency and the occurrence of tornadic supercells. These positive results highlight the need for future research to investigate the impact of CAPE tendency on the severity of convection

Position paper on the potential of inadvertent weather modification of the Florida peninsula resulting from the stabilized ground cloud

Based on the climatology of the Florida Peninsula, we assessed the risk for weather modification. Certain weather situations warrant launch rescheduling because of the risk of possible impact on hurricanes, hail formation and lightning activity, strong wind developments, and intensification of high rainfall rates. The cumulative effects of 40 launches per year on weather modification were found to be insignificant

Potential vorticity conservation in upper tropospheric fronts.

Massachusetts Institute of Technology. Dept. of Meteorology. Thesis. 1966. M.S.Bibliography: leaves 78-79.M.S

Position paper on the potential of inadvertent weather modification of the Florida Peninsula resulting from neutralization of space shuttle solid rocket booster exhaust clouds

A concept of injecting compounds into the exhaust cloud was proposed to neutralize the acidic nature of the low-level stabilized ground cloud (SGC) was studied. The potential Inadvertent Weather Modification caused by exhaust cloud characteristics from three hours to seven days after launch was studied. Possible effects of the neutralized SGC in warm and cloud precipitation processes were discussed. Based on a detailed climatology of the Florida Peninsula, the risk for weather modification under a variety of weather situations was assessed

Differences Between High Shear / Low CAPE Environments in the Northeast US Favoring Straight-Line Damaging Winds versus Tornadoes

High shear / low CAPE (HSLC) environments are common in the Northeast US and can occur at any time of year. Severe weather in HSLC environments is notoriously hard to predict, often catching both forecasters and the general public off-guard. The goal of this project is to help forecasters to identify HSLC environments favorable for severe weather in the Northeast US, and to discriminate between HSLC environments that are supportive of tornadoes versus those that favor straight-line damaging winds (SDW). A 10-year HSLC severe weather environmental climatology was created for the Northeast US (New England, New York, New Jersey, Pennsylvania). This climatology includes 54 different parameters that can be used to identify and describe severe weather environments. HSLC criteria was defined as surface-based CAPE (SBCAPE) ≤ 500 J kg−1, most unstable parcel CAPE (MUCAPE) and mixed-layer CAPE (MLCAPE) ≤ 1000 J kg−1, and 0–6-km wind shear ≥ 18 m s−1 (Sherburn et al. 2016). Events included in the climatology consisted of numerous (≥5) straight-line damaging wind reports, or at least 1 tornado report. Each event was classified by the season in which it occurred and the mode (discrete, cluster of cells, quasi-linear convective system (QLCS)) of the storm which produced the reports. Results show that warm-season HSLC severe events typically occurred either at the beginning or at the tail end of an event in an environment where CAPE values were predominantly too large to meet the HSLC criteria. Storm mode was variable for warm-season events, but cool-season events were dominated by QLCSs. Results show lifted condensation levels (LCLs) as well as low-level shear and wind direction as some of the most skillful parameters at discriminating between tornadic and non-tornadic events. There are various other useful parameters, including but not limited to, surface relative humidity, effective shear magnitude, and convective inhibition. The usefulness of these, and other parameters, at discriminating between HSLC environments favorable for SDW versus tornadoes will be discussed

A Preliminary Climatology of Tropical Moisture Exports in the Southern Hemisphere

Heavy precipitation events in the midlatitudes can be supported by the poleward transport of tropical air masses within the warm sector of extratropical cyclones. Previous studies have established a climatology of the four preferred pathways of tropical moisture export (TME) events into the midlatitudes over the Northern Hemisphere (NH). The present study constructs a similar climatology of TME timing and frequency over the Southern Hemisphere (SH), highlighting three preferential regions for tropicalmidlatitude interaction. These regions correspond to the locations of the: (i) South Pacific convergence zone (Pacific Ocean pathway, PO), (ii) South Atlantic convergence zone (South American pathway, SA), and (iii) South Indian convergence zone (Southeast African pathway, SEA). A Eulerian precipitable water (PW) climatology is constructed to isolate individual TME events within the three preferred pathways in the SH. The climatology identifies PW values along 30°S at 5° increments, extracting values four-times-daily from the 2.5° NCEP-NCAR reanalysis dataset for 1979−2007. Potential TME events are identified when two neighboring grid points have PW values \u3e93rd percentile of their monthly PW distribution for \u3e24 h. Potential events are classified as TMEs following human verification of the event‘s tropospheric structure. The present investigation reveals that TME frequency in the SH varies on intraseasonal and interannual timescales. The PO pathway exhibits the least seasonal variability of the three examined locations, while the SEA pathway is over three times as active during the SH meteorological summer (DJF). An in-depth analysis of the overall synoptic/dynamic mechanisms associated with TME events in the SEA pathway is performed in this study, linking the observed DJF peak in TME activity to the to the active phase of the South Indian convergence zone

The Extratropical Transition of Tropical Cyclones. Part I: Cyclonic Evolution and Direct Impacts

Extratropical transition (ET) is the process by which a tropical cyclone, upon encountering a baroclinic environment and reduced sea surface temperature at higher latitudes, transforms into an extratropical cyclone. This process is influenced by, and influences, phenomena from the tropics to the midlatitudes and from the meso- to the planetary scales to extents that vary between individual events. Motivated in part by recent high-impact and/or extensively observed events such as North Atlantic Hurricane Sandy in 2012 and western North Pacific Typhoon Sinlaku in 2008, this review details advances in understanding and predicting ET since the publication of an earlier review in 2003. Methods for diagnosing ET in reanalysis, observational, and model-forecast datasets are discussed. New climatologies for the eastern North Pacific and southwest Indian Oceans are presented alongside updates to western North Pacific and North Atlantic Ocean climatologies. Advances in understanding and, in some cases, modeling the direct impacts of ET-related wind, waves, and precipitation are noted. Improved understanding of structural evolution throughout the transformation stage of ET fostered in large part by novel aircraft observations collected in several recent ET events is highlighted. Predictive skill for operational and numerical model ET-related forecasts is discussed along with environmental factors influencing posttransition cyclone structure and evolution. Operational ET forecast and analysis practices and challenges are detailed. In particular, some challenges of effective hazard communication for the evolving threats posed by a tropical cyclone during and after transition are introduced. This review concludes with recommendations for future work to further improve understanding, forecasts, and hazard communication

The Wintertime Southern Hemisphere Split Jet: Structure, Variability, and Evolution

A persistent feature of the Southern Hemisphere upper-level time-mean flow is the presence of a split jet across the South Pacific east of Australia during the austral winter. The split jet is composed of the subtropical jet (STJ) on its equatorward branch and the polar front jet (PFJ) on its poleward branch. The NCEP-NCAR reanalysis is used to investigate the structure and evolution of the split jet. Results show that the presence/absence of the PFJ determines the degree of split flow, given that the STJ is a quasi-steady feature. A split-flow index (SFI) is developed to quantify the variability of the split jet, in which negative values represent strong split flow and positive values nonsplit flow. Correlations with teleconnection indices are investigated, with the SFI positively correlated to the Southern Oscillation index and negatively correlated to the Antarctic oscillation. The SFI is used to construct composites of heights, temperature, and wind for split-flow and non-split-flow days. The composites reveal that relatively cold conditions occur in the South Pacific in association with non-split-flow regimes, and split-flow regimes occur when relatively warm conditions prevail. In the latter situation cold air bottled up over Antarctica helps to augment the background tropospheric thickness gradient between Antarctica and the lower latitudes with a resulting increase in the thermal wind and the PFJ. It is surmised that frequent cold surges out of Antarctica moving into the South Pacific are associated with non-split-flow regimes. In this context, the variability of the split jet responds to large-scale baroclinic processes and is further modulated by synoptic-scale disturbances