George S. Young

Bulk parameterization of air-sea fluxes for Tropical Ocean-Global Atmosphere Coupled-Ocean Atmosphere Response Experiment

This paper describes the various physical processes relating near-surface atmospheric and oceanographic bulk variables ; their relationship to the surface fluxes of momentum, sensible heat, and latent heat ; and their expression in a bulk flux algorithm. The algorithm follows the standard Monin-Obukhov similarity approach for near-surface meteorological measurements but includes separate models for the oceans cool skin and the diurnal warm layer, which are used to derive true skin temperature from the bulk temperature measured at some depth near the surface. The basic structure is an outgrowth of the Liu-Katsaros-Businger [Liu et al., 1979] method, with modifications to include a different specification of the roughness/stress relationship, a gustiness velocity to account for the additional flux induced by boundary layer scale variability, and profile functions obeying the convective limit. Additionally, we have considered the contributions of the sensible heat carried by precipitation and the requirement that the net dry mass flux be zero (the so-called Webb correction [Webb et al., 1980]). The algorithm has been tuned to fit measurements made on the R/V Moana Wave in the three different cruise legs made during the Coupled Ocean-Atmosphere Response Experiment. These measurements yielded 1622 fifty-min averages of fluxes and bulk variables in the wind speed range from 0.5 to 10 m s -1 . The analysis gives statistically reliable values for the Charnock [1955] constant (a = 0.011) and the gustiness parameter (β = 1.25). An overall mean value for the latent heat flux, neutral bulk-transfer coefficient was 1.11 x 10 -3 , declining slightly with increasing wind speed. Mean values for the sensible and latent heat fluxes were 9.1 and 103.5 W m -2 ; mean values for the Webb and rain heat fluxes were 2.5 and 4.5 W m -2 . Accounting for all factors, the net surface heat transfer to the ocean was 17.9 ± 10 W m -2 .

Cool‐skin and warm‐layer effects on sea surface temperature

To obtain bulk surface flux estimates approaching the ±10 W m−2 accuracy desired for the Tropical Ocean-Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (COARE) program, bulk water temperature data from ships and buoys must be corrected for cool-skin and diurnal warm-layer effects. In this paper we describe two simple scaling models to estimate these corrections. The cool-skin model is based on the standard Saunders [1967] treatment, including the effects of solar radiation absorption, modified to include both shear-driven and convectively driven turbulence through their relative contributions to the near-surface turbulent kinetic energy dissipation rate. Shear and convective effects are comparable at a wind speed of about 2.5 m s−1. For the R/V Moana Wave COARE data collected in the tropical western Pacific, the model gives an average cool skin of 0.30 K at night and an average local noon value of 0.18 K. The warm-layer model is based on a single-layer scaling version of a model by Price et al. [1986]. In this model, once solar heating of the ocean exceeds the combined cooling by turbulent scalar heat transfer and net longwave radiation, then the main body of the mixed layer is cut off from its source of turbulence. Thereafter, surface inputs of heat and momentum are confined to a depth DT that is determined by the subsequent integrals of the heat and momentum. The model assumes linear profiles of temperature-induced and surface-stress-induced current in this “warm layer.” The model is shown to describe the peak afternoon warming and diurnal cycle of the warming quite accurately, on average, with a choice of a critical Richardson number of 0.65. For a clear day with a 10-m wind speed of 1 m s−1, the peak afternoon warming is about 3.8 K with a warm-layer depth of 0.7 m, decreasing to about 0.2 K and 19 m at a wind speed of 7 m s−1. For an average over 70 days sampled during COARE, the cool skin increases the average atmospheric heat input to the ocean by about 11 W m−2; the warm layer decreases it by about 4 W m−2 (but the effect can be 50 W m−2 at midday).

Rolls, Streets, Waves, and More: A Review of Quasi-Two-Dimensional Structures in the Atmospheric Boundary Layer

Abstract The atmospheric boundary layer is home to a number of horizontally elongated quasi-two-dimensionalphenomena including cloud streets, roll vortices, thermal waves, and surface layer streaks. These phenomena, their dynamics, and their interactions are explored via a review of the literature. Making a clear distinction betweenthe various quasi-two-dimensional phenomena allows improved synthesis of previous results and a betterunderstanding of the interrelationships between phenomena.

A New Model of the Oceanic Evaporation Duct

Abstract Failure to consider anomalous propagation of microwave radiation in the troposphere may result in erroneous meteorological radar measurements. The most commonly occurring anomalous propagation phenomenon over the ocean is the evaporation duct. The height of this duct is dependent on atmospheric variables and is a major input to microwave propagation prediction models. This evaporation duct height is determined from an evaporation duct model using bulk measurements. Two current evaporation duct models in widespread operational use are examined. We propose and test a new model that addresses deficiencies in these two models. The new model uses recently refined bulk similarity expressions developed for the determination of the ocean surface energy budget in the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment. Comparison of these models is made using data collected from a boat off Wallops Island, Virginia, during a range of seasons and weather conditions and from the tid...

Turbulence Structure of the Convective Boundary Layer. Part II. Phonenix 78 Aircraft Observations of Thermals and Their Environment

Abstract A conditional sampling technique based upon the mixed layer spectra of vertical velocity and temperature is developed. This technique is used to analyze the turbulence data obtained by aircraft during the Phoenix 78 convective boundary layer experiment. Observations of the size, spacing and structure of thermals as well as their contribution to mixed layer processes are presents. Implications of these results for pollution dispersion are discussed. The observed scale dependence is also used to estimate what fraction of a turbulence statistic must be accounted for by the subgrid parameterizations of large eddy simulations.

The Interannual Variability of Tropical Cyclones

Abstract This paper examines the interannual variability of tropical cyclones in each of the earth’s cyclone basins using data from 1985 to 2003. The data are first analyzed using a Monte Carlo technique to investigate the long-standing myth that the global number of tropical cyclones is less variable than would be expected from examination of the variability in each basin. This belief is found to be false. Variations in the global number of all tropical cyclones are indistinguishable from those that would be expected if each basin was examined independently of the others. Furthermore, the global number of the most intense storms (Saffir–Simpson categories 4–5) is actually more variable than would be expected because of an observed tendency for storm activity to be correlated between basins, and this raises important questions as to how and why these correlations arise. Interbasin correlations and factor analysis of patterns of tropical cyclone activity reveal that there are several significant modes of v...

Heat and Moisture Budgets of Tropical Mesoscale Anvil Clouds

Abstract An analysis of the heat and moisture budgets of tropical mesoscale anvil clouds has been carried out. Mesoscale anvils, defined as widespread (∼100 km) cloud systems extending from near the freezing level to the high troposphere, are characterized by light, stratiform precipitation. These cloud features, which are preceded by and generally merged with cumulonimbus clouds, are prevalent throughout the tropics and summertime midlatitudes and may account for an important fraction of the total tropical rainfall. Sounding data from the December 1978 field phase of the International Winter Monsoon Experiment (Winter MONEX) are used to determine heat and moisture (Q1t and Q2) budgets for a number of mesoscale anvil cloud systems. The composite heating (Q1) profile shows a warming peak in the upper troposphere near 350 hPa or 8–9 km that can be attributed to condensation and freezing in the anvil and a cooling peak in the lower troposphere near 700 hPa or 3 km due to rainfall evaporation and melting. The...

Convective Wakes in the Equatorial Western Pacific during TOGA

Abstract The evolution of convective wakes was studied using composite time series calculated from data collected in the western Pacific warm pool during a pilot cruise and intensive observation period (IOP) of the Tropical Ocean Global Atmosphere (TOGA) Coupled Ocean-Atmosphere Response Experiment (COARE). Hourly averaged observations from 42 convective wakes were used to compute wake-relative composite time series of the bulk meteorological variables, as well as sensible and latent heat fluxes. These analyses show great similarities between the convective wake characteristics of the pilot cruise and the IOP, despite differences in season and location. This result, combined with a strong correlation between individual wakes and the composite time series, demonstrates the representativeness of the composites. TOGA convective wakes were found to cause a significant decrease in air temperature, a significant increase in wind speed, and thus significant increases in sensible and latent heat fluxes, which is ...

Source Characterization with a Genetic Algorithm-Coupled Dispersion-Backward Model Incorporating SCIPUFF

Abstract This paper extends the approach of coupling a forward-looking dispersion model with a backward model using a genetic algorithm (GA) by incorporating a more sophisticated dispersion model [the Second-Order Closure Integrated Puff (SCIPUFF) model] into a GA-coupled system. This coupled system is validated with synthetic and field experiment data to demonstrate the potential applicability of the coupled model to emission source characterization. The coupled model incorporating SCIPUFF is first validated with synthetic data produced by SCIPUFF to isolate issues related directly to SCIPUFF’s use in the coupled model. The coupled model is successful in characterizing sources even with a moderate amount of white noise introduced into the data. The similarity to corresponding results from previous studies using a more basic model suggests that the GA’s performance is not sensitive to the dispersion model used. The coupled model is then tested using data from the Dipole Pride 26 field tests to determine i...

Turbulence Structure of the Convective Boundary Layer. Part I. Variability of Normalized Turbulence Statistics

Abstract Profiles of turbulence statistics from aircraft observations of the Phoenix 78 convective boundary layer experiment are compared with those from previous observational and modeling studies. The sources and degree of variability of the normalized results, both within and between experiments, are discussed. The intercomparison provides evidence that moderately rolling terrain does not bias convective boundary layer turbulence structure away from that observed over more uniform terrain. The manner in which cross inversion entrainment affects turbulence in the atmosphere and in models is also discussed.