Edward I. Tollerud

Turbulence and Gravity Waves within an Upper-Level Front

Abstract High-resolution dropwindsonde and in-flight measurements collected by a research aircraft during the Severe Clear-Air Turbulence Colliding with Aircraft Traffic (SCATCAT) experiment and simulations from numerical models are analyzed for a clear-air turbulence event associated with an intense upper-level jet/frontal system. Spectral, wavelet, and structure function analyses performed with the 25-Hz in situ data are used to investigate the relationship between gravity waves and turbulence. Mesoscale dynamics are analyzed with the 20-km hydrostatic Rapid Update Cycle (RUC) model and a nested 1-km simulation with the nonhydrostatic Clark–Hall (CH) cloud-scale model. Turbulence occurred in association with a wide spectrum of upward propagating gravity waves above the jet core. Inertia–gravity waves were generated within a region of unbalanced frontogenesis in the vicinity of a complex tropopause fold. Turbulent kinetic energy fields forecast by the RUC and CH models displayed a strongly banded appeara...

Structure of a Midtropospheric Vortex Induced by a Mesoscale Convective System

On 9 June 1988 a mesoscale (;200-km diameter) convectively generated vortex (MCV) passed through the Colorado wind-profiling network. The generating convective system, which was too small to meet Maddox’s mesoscale convective complex criteria, developed beneath a high-amplitude mid- and upper-level ridge axis. Profiler winds obtained within the stratiform region of the convective system and near the center of the ensuing MCV form the basis of this study. With the addition of satellite (including rapid scan) images and conventional and Doppler radar data, this vortex was well observed over its entire life cycle. The slowly moving vortex was observed by the Flagler 50-MHz profiler for more than 16 h. For a portion of this period the circulation was quasi-steady; hence, the spatial structure of the vortex was depicted by timeto-space conversion of the profiler data. The results show a strong, coherent circulation with maximum tangential speeds greater than 16 m s21 at 6 km above mean sea level (MSL) and at radii of 50‐70 km; corresponding relative vorticity was more than three times as large as the local Coriolis parameter. The long duration and the apparent dominance of vorticity over divergence suggest that the flow in the vortex was in a quasi-balanced state. Hence, the temperature perturbation necessary to support the tangential velocity distribution was computed assuming gradient balance in the radial direction. The resulting estimated temperature structure showed a warm core with a magnitude of 2.38C at 7.3 km MSL and a cold core below 6.3 km MSL. The associated potential vorticity (PV) structure at the vortex center consisted of a lens of high PV with a maximum at 6.3 km MSL and relative minima above and below this height.

A Composite Life Cycle of Nonsquall Mesoscale Convective Systems over the Tropical Ocean. Part I: Kinematic Fields

Abstract The wind fields associated with cloud clusters observed during the Global Atmospheric Research Programs Atlantic Tropical Experiment (GATE) are investigated. A compositing procedure is devised to isolate the cluster circulations. Satellite-observed cloud cover estimates by Cox and Griffith form the basis for the identification and classification of clusters and for the determination of their life cycles. The compositing criteria focus on the upper-tropospheric portions of anvil clouds that are a prominent feature of cloud clusters. The compositing procedure is applied to a set of objectively analyzed upper-air winds for Phase 3 of GATE prepared by K. V. Ooyama and J.-H. Chu. The results show that slow-moving cloud clusters tend to form in regions of relatively small vertical wind shear and that the shear at the cluster center decreases during the cluster life cycle. Squall clusters, on the other hand, have significantly larger lower-tropospheric shear. Changes in the total horizontal wind field ...

An Observational Study of the Upper-Tropospheric Vorticity Fields in GATE Cloud Clusters

Abstract A large-amplitude asymmetric vorticity couplet has been observed in the upper troposphere near a lame cloud cluster in GATE (GARP Atlantic Tropical Experiment) on 5 September 1974. The couplet consists of a cyclonic center to the north of the cluster and an anticyclonic center to the south. The couplet is a result of the deceleration of the upper-tropospheric easterly winds in a region near the center of the cluster. These features also appear on a composite of large slow-moving clusters occurring during Phase 3 of GATE. Vorticity budget analysis shows that the couplets are produced by subcluster-scale process and, to a lesser degree, by cluster-scale twisting. On the basis of this finding and on the basis of the three-dimensional structure of horizontal momentum fields, it is suggested that a part of the deceleration producing the couplet is a result of momentum redistribution by subcluster-scale circulations (such as cumulonimbi or mesoscale cloud lines). The composite wind fields of the large ...

Mesoscale moisture transport by the low-level jet during the IHOP field experiment

Abstract Previous studies of the low-level jet (LLJ) over the central Great Plains of the United States have been unable to determine the role that mesoscale and smaller circulations play in the transport of moisture. To address this issue, two aircraft missions during the International H2O Project (IHOP_2002) were designed to observe closely a well-developed LLJ over the Great Plains (primarily Oklahoma and Kansas) with multiple observation platforms. In addition to standard operational platforms (most important, radiosondes and profilers) to provide the large-scale setting, dropsondes released from the aircraft at 55-km intervals and a pair of onboard lidar instruments—High Resolution Doppler Lidar (HRDL) for wind and differential absorption lidar (DIAL) for moisture—observed the moisture transport in the LLJ at greater resolution. Using these observations, the authors describe the multiscalar structure of the LLJ and then focus attention on the bulk properties and effects of scales of motion by computi...

Cloud-Cluster-Scale Circulations and the Vorticity Budget of Synoptic-Scale Waves Over the Eastern Atlantic Intertropical Convergence Zone

Abstract Objectively analyzed upper-air winds over the intertropical convergence zone of the eastern tropical Atlantic are separated into components representing the mean flow, westward moving synoptic-scale waves and cloud-cluster-scale motions during the third observational period of the GARP Atlantic Tropical Experiment. Vorticity budget analysis is performed for the three components of the flow. At the scale of cloud clusters, the vorticity budgets show variability that is the same order of magnitude as the vorticity field changes caused by the passage of the easterly waves. The variability patterns appear to be closely related to the phase of the wave and to cloud-cluster activity. It is concluded that the nonlinear contributions of cloud-cluster-scale motions to the average wave structure are small in the lower troposphere, but are as large as any of the vorticity budget terms involving wave divergence or vertical motion in the middle and upper troposphere. The implications of the results for numeri...

A Composite Life Cycle of Nonsquall Mesoscale Convective Systems over the Tropical Ocean. Part II: Heat and Moisture Budgets

Abstract The heat and moisture budgets associated with five large nonsquall cloud clusters observed during Phase 3 of the Global Atmospheric Research Programs Atlantic Tropical Experiment (GATE) are investigated. The input data for the budget computations are objectively analyzed fields of wind, temperature and relative humidity that were based on conventional upper-air soundings. Estimates of the radiative heating rate were obtained from Cox and Griffith. A compositing technique is used to summarize the budget results for the growing, mature and dissipating stages of the clusters. The budgets in the growing stage are characterized by a very large low-level, apparent moisture sink separated in height from the region where the apparent heating is realized. In the mature stage, the apparent heating maximum shifts upward, accompanied by the development of a corresponding secondary maximum of apparent drying. A composite of radiative heating estimates from Cox and Griffith shows that the horizontal radiative...

The Consistent Parameterization of the Effects of Cumulus Clouds on the Large-Scale Momentum and Vorticity Fields

Abstract A physical and mathematical framework for the mutually consistent parameterization of the effects of cumulus convection on the large-scale momentum and vorticity fields is proposed. The key to achieving consistency is the understanding that the vorticity dynamics of the clouds below the spatial resolution of a large-scale dynamical model may be neglected in the vorticity budget when the clouds are considered to be independent buoyant elements sharing a common large-scale environment This simplified approach is used to obtain a consistent pair of large-scale momentum and vorticity equations based on Ooyamas theory of cumulus parameterization. The results focus attention on the need to obtain a better understanding of the detrainment process and the pressure interactions between the clouds and their environment.