Teddy Holt

The Labrador Sea Deep Convection Experiment

In the autumn of 1996 the field component of an experiment designed to observe water mass transformation began in the Labrador Sea. Intense observations of ocean convection were taken in the following two winters. The purpose of the experiment was, by a combination of meteorological and oceanographic field observations, laboratory studies, theory, and modeling, to improve understanding of the convective process in the ocean and its representation in models. The dataset that has been gathered far exceeds previous efforts to observe the convective process anywhere in the ocean, both in its scope and range of techniques deployed. Combined with a comprehensive set of meteorological and air-sea flux measurements, it is giving unprecedented insights into the dynamics and thermodynamics of a closely coupled, semienclosed system known to have direct influence on the processes that control global climate.

Effect of Land–Atmosphere Interactions on the IHOP 24–25 May 2002 Convection Case

Abstract Numerical simulations are conducted using the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) to investigate the impact of land–vegetation processes on the prediction of mesoscale convection observed on 24–25 May 2002 during the International H2O Project (IHOP_2002). The control COAMPS configuration uses the Weather Research and Forecasting (WRF) model version of the Noah land surface model (LSM) initialized using a high-resolution land surface data assimilation system (HRLDAS). Physically consistent surface fields are ensured by an 18-month spinup time for HRLDAS, and physically consistent mesoscale fields are ensured by a 2-day data assimilation spinup for COAMPS. Sensitivity simulations are performed to assess the impact of land–vegetative processes by 1) replacing the Noah LSM with a simple slab soil model (SLAB), 2) adding a photosynthesis, canopy resistance/transpiration scheme [the gas exchange/photosynthesis-based evapotranspiration model (GEM)] to the Noah LSM, and 3) repla...

Urban Canopy Modeling of the New York City Metropolitan Area: A Comparison and Validation of Single- and Multilayer Parameterizations

Abstract High-resolution numerical simulations are conducted using the Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS)1 with two different urban canopy parameterizations for a 23-day period in August 2005 for the New York City (NYC) metropolitan area. The control COAMPS simulations use the single-layer Weather Research and Forecasting (WRF) Urban Canopy Model (W-UCM) and sensitivity simulations use a multilayer urban parameterization based on Brown and Williams (BW-UCM). Both simulations use surface forcing from the WRF land surface model, Noah, and hourly sea surface temperature fields from the New York Harbor and Ocean Prediction System model hindcast. Mean statistics are computed for the 23-day period from 5 to 27 August (540-hourly observations) at five Meteorological Aviation Report stations for a nested 0.444-km horizontal resolution grid centered over the NYC metropolitan area. Both simulations show a cold mean urban canopy air temperature bias primarily due to an underestimation of n...

Highlights of Coastal Waves 1996

Some of the highlights of an experiment designed to study coastal atmospheric phenomena along the California coast (Coastal Waves 1996 experiment) are described. This study was designed to address ...

Large-Scale Structure of the June-July 1996 Marine Boundary Layer along California and Oregon

Abstract Data from surface stations, profilers, long-range aircraft surveys, and satellites were used to characterize the large-scale structure of the marine boundary layer off of California and Oregon during June and July 1996. To supplement these observations, June–July 1996 averages of meteorological fields from the U.S. Navy’s operational Coupled Ocean–Atmospheric Mesoscale Prediction System (COAMPS) model were generated for the region. Model calculations show a broad band of fast northerly surface winds exceeding 7 m s−1 extending along the California–Oregon coast. Buoy-measured peaks of 7.1 m s−1 off Bodega Bay, 7.2 m s−1 off Point Piedras Blancas, and 8.8 m s−1 near Point Conception were reported. Mean winds at the buoys located 15–25 km offshore are generally faster than those at coastal stations, and all station winds are faster in the afternoon. The aircraft and station observations confirm that an air temperature inversion typically marks the top of the marine boundary layer, which deepens offs...

A Planetary-Scale to Mesoscale Perspective of the Life Cycles of Extratropical Cyclones: The Bridge between Theory and Observations

The emergence of meteorology as a rational science began around the turn of the twentieth century when Max Margules, Hermann Helmholtz, Felix Exner, and Vilhehn Bjerknes formulated the theoretical basis for what was previously considered an empirical science with a qualitative application to weather forecasting and climatology. The concurrent synoptic studies of Sir Napier Shaw, Rudolph Lempfert, Johan Sandstrom, V. Bjerknes, and Heinrich von Ficker, among others, provided insight into the structure and evolution of weather systems, and an assessment of the represen-tativeness of the proposed theories. The synergy between dynamic and synoptic meteorology inspired new theories, observing strategies, conceptual models, and dramatic advances in weather forecasting. During the period 1913–1922, the Leipzig and Norwegian schools of meteorology made fundamental contributions to the advancement of the emerging science. With V. Bjerknes as their director and mentor, the research associates and students at the Geophysical Institutes in Leipzig, Germany, and Bergen, Norway, synthesized theory, observations, synoptic analysis and diagnosis in their quest for physical understanding and improved weather prediction. Their efforts gave rise to revolutionary paradigms for the theory, structure, and evolution of frontal cyclones, many of which remain widely applied in research and weather forecasting. A historical perspective of the science and the milieu of the period is reviewed in the works of Bergeron (1959), Kutzbach (1979), Friedman (1989), and in the historical chapters in this volume by Eliassen (1998), Friedman (1998), Newton and Newton (1998), and Volkert (1998).

Coastally Trapped Wind Reversals: Progress toward Understanding

Abstract Coastally trapped wind reversals along the U.S. west coast, which are often accompanied by a northward surge of fog or stratus, are an important warm—season forecast problem due to their impact on coastal maritime activities and airport operations. Previous studies identified several possible dynamic mechanisms that could be responsible for producing these events, yet observational and modeling limitations at the time left these competing interpretations open for debate. In an effort to improve our physical understanding, and ultimately the prediction, of these events, the Office of Naval Research sponsored an Accelerated Research Initiative in Coastal Meteorology during the years 1993—98 to study these and other related coastal meteorological phenomena. This effort included two field programs to study coastally trapped disturbances as well as numerous modeling studies to explore key dynamic mechanisms. This paper describes the various efforts that occurred under this program to provide an advanc...

Intercomparison of Mesoscale Model Simulations of the Daytime Valley Wind System

AbstractThree-dimensional simulations of the daytime thermally induced valley wind system for an idealized valley–plain configuration, obtained from nine nonhydrostatic mesoscale models, are compared with special emphasis on the evolution of the along-valley wind. The models use the same initial and lateral boundary conditions, and standard parameterizations for turbulence, radiation, and land surface processes. The evolution of the mean along-valley wind (averaged over the valley cross section) is similar for all models, except for a time shift between individual models of up to 2 h and slight differences in the speed of the evolution. The analysis suggests that these differences are primarily due to differences in the simulated surface energy balance such as the dependence of the sensible heat flux on surface wind speed. Additional sensitivity experiments indicate that the evolution of the mean along-valley flow is largely independent of the choice of the dynamical core and of the turbulence parameteriz...

Mesoscale forcing of a boundary layer jet along the California coast

Mesoscale numerical model simulations were examined to investigate the thermal and topographic forcing of a boundary layer jet along the northern California coast from 0000 UTC May 2 to 1200 UTC May 3, 1990. Routine surface and upper air observations, satellite, and higher-resolution coastal observations (R/V Point Sur and Doppler wind profiler data) documented the diurnal evolution of a coastal marine atmospheric boundary layer (MABL), coastal cloud structure, and mesoscale features such as the coastal jet and land-sea breeze circulations that were reasonably well forecast by the numerical model. Sensitivity model simulations to coastal baroclinicity showed that the diurnal development and intensification of the coastal MABL jet located north of the San Francisco Bay area was a result of thermal forcing due to differential land-sea heating. Simulations in which the coastal baroclinicity was held fixed in time at a minimal strength showed no diurnal development of the MABL jet. The strength of the jet was approximated well by the thermal wind relationship, with the jet core located in the sloping marine inversion layer within one Rossby radius of deformation from the coastline. The steepness of the marine inversion at the coastline was enhanced by regions of strong MABL divergence just offshore and strong convergence onshore resulting from the sea breeze circulation. Modifications to coastal terrain in two separate sensitivity model simulations illustrated that the primary effect of coastal topography was to act as a barrier to the onshore intrusion of higher momentum offshore air. This blocking was due to a topographically forced vertical circulation with a strong descending branch located at the coast. This downslope flow and adiabatic warming steepened the MABL inversion at the coast and enhanced the coastal baroclinicity and the coastal jet. Simulations without coastal terrain showed a jet structure that was spatially diffuse across the coastline and displaced more shoreward. Simulations in which coastal valleys were removed and replaced by a larger coastal mountain range resulted in little modification to the coastal jet intensity or offshore displacement.

Impact of assimilating SSM/I rainfall rates on numerical prediction of winter cyclones

Abstract A series of observing system simulation experiments (OSSE) and real data assimilation experiments were conducted to assess the impact of assimilating Special Sensor Microwave/Imager (SSM/I)-estimated rainfall rates on limited-area model predictions of intense winter cyclones. For the OSSE, the slow-moving, fronto- and cyclogenesis along the cast coast of United States during the second intensive observation period (IOP 2) of the Genesis of Atlantic Lows Experiment (GALE) (26-28 January 1986) was selected as the test case. The perfect “observed” rainfall rates were obtained by an integration of a version of the Naval Research Laboratory (NRL) limited-area model, whereas the “forecast” was generated by a degraded version of the NRL model. A number of OSSEs were conducted in which the “observed” rainfall rates were assimilated into the “forecast” model. Rainfall rates of various data frequencies, different vertical beating profiles, various assimilation windows, and prescribed systematic errors were...