Comments on “On the Estimation of Overwater Bowen Ratio from Sea–Air Temperature Difference”*

Sadhuram, Y.; Murthy, T. V. R.; Sarma, Y.V.B.; Murty, V. S. N.

doi:10.1175/1520-0485(2001)031<1933:cooteo>2.0.co;2

Cited by 7 publications

(4 citation statements)

References 4 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The perturbation of saturation equivalent potential temperature used for the KM model is given by the dashed line in the bottom-right corner of Fig. Note that the zero surface flux of sensible heat assumed for the WK model is consistent with the weak Bowen ratios found over the tropical oceans (Hsu 1998;Sadhuram et al 2001). Note that the zero surface flux of sensible heat assumed for the WK model is consistent with the weak Bowen ratios found over the tropical oceans (Hsu 1998;Sadhuram et al 2001).…”

Section: Model Results and Comparison To Observationsmentioning

confidence: 54%

“…In section 3, we present the first set of results for the ocean case, characterized by no or very little contribution of sensible heat fluxes, that is, very small Bowen ratios (Hsu 1998;Sadhuram et al 2001), where both the KM and the WK models show similar results, characterized by a morning precipitation peak consistent with observations. In section 2, we discuss briefly the two multicloud models, with and without boundary layer dynamics, named hereafter WK and KM models, forced from the surface by the diurnal cycle of solar heating.…”

Section: Introductionmentioning

confidence: 80%

See 1 more Smart Citation

Simple Multicloud Models for the Diurnal Cycle of Tropical Precipitation. Part I: Formulation and the Case of the Tropical Oceans

Frenkel

Khouider

Majda

2011

Journal of the Atmospheric Sciences

View full text Add to dashboard Cite

The variation of tropical precipitation due to the diurnal cycle of solar heating is examined here in the context of two simple models for tropical convection. The models utilize three cloud types-congestus, deep, and stratiform-that are believed to characterize organized tropical convection and are based on the two first baroclinic modes of vertical structure plus a boundary layer mode. The two models differ mainly in the way they treat the boundary layer dynamics. The first one is purely thermodynamical and is reduced to a single equation for the equivalent potential temperature u e connecting the boundary layer to the upper troposphere through downdrafts and to the surface through evaporation while the second uses full bulk boundary layer (FBBL) dynamics with a careful separation between sensible and latent heat fluxes and parameterization of nonprecipitating shallow cumulus. It turns out that in the case of the precipitation over the ocean where the Bowen ratio is small, both models yield a qualitatively similar solution, characterized by an overnight initiation and early morning peak in precipitation consistent with observations. The modeled diurnal cycle of precipitation over the ocean is divided into four cyclic phases: 1) a CAPE (re)generation phase characterized by the enhancement of the boundary layer u e and moisture fluxes during midday and early afternoon that is followed by 2) a (re)moistening phase dominated by congestus heating during the late afternoon and moistening from downdrafts (due to detrainment of shallow cumulus, specifically in the FBBL model) and radiative cooling that lasts until midnight. 3) Deep convection is initiated around midnight when the midtroposphere is sufficiently moist and cool and (re)establishes the precipitation level near its radiative convective equilibrium (1 K day 21 ) and then 4) peaks with sunrise at 0600 LST to yield a precipitation maximum of roughly 2 K day 21 at around 0900 LST that dries the troposphere and consumes CAPE and closes the cycle.

show abstract

Section: Model Results and Comparison To Observationsmentioning

confidence: 54%

Section: Introductionmentioning

confidence: 80%

Simple Multicloud Models for the Diurnal Cycle of Tropical Precipitation. Part I: Formulation and the Case of the Tropical Oceans

Frenkel

Khouider

Majda

2011

Journal of the Atmospheric Sciences

View full text Add to dashboard Cite

show abstract

“…For instance, such conditions were encountered over the Amazonian forest by Da Rocha et al (2003), who estimated a mean annual Bowen ratio β of 0.17, or by Sadhuram et al (2001), who found that β can be even smaller than 0.1 during monsoon periods or over open ocean waters. In our experimental site, 38% of the days in 2007 corresponded to a Bowen ratio smaller than 0.4.…”

Section: Sensible Heat Flux Values Calculated Via the "β-Closure Methmentioning

confidence: 97%

Uncertainty analysis of computational methods for deriving sensible heat flux values from scintillometer measurements

et al. 2009

View full text Add to dashboard Cite

Abstract. The use of scintillometers to determine sensible heat fluxes is now common in studies of land-atmosphere interactions. The main interest in these instruments is due to their ability to quantify energy distributions at the landscape scale, as they can calculate sensible heat flux values over long distances, in contrast to Eddy Covariance systems. However, scintillometer data do not provide a direct measure of sensible heat flux, but require additional data, such as the Bowen ratio (β), to provide flux values. The Bowen ratio can either be measured using Eddy Covariance systems or derived from the energy balance closure. In this work, specific requirements for estimating energy fluxes using a scintillometer were analyzed, as well as the accuracy of two flux calculation methods. We first focused on the classical method (used in standard softwares) and we analysed the impact of the Bowen ratio on flux value and uncertainty. For instance, an averaged Bowen ratio (β) of less than 1 proved to be a significant source of measurement uncertainty. An alternative method, called the "β-closure method", for which the Bowen ratio measurement is not necessary, was also tested. In this case, it was observed that even for low β values, flux uncertainties were reduced and scintillometer data were well correlated with the Eddy Covariance results. Besides, both methods should tend to the same results, but the second one slightly underestimates H while β decreases (<5%).

show abstract

“…Over the ocean, the Bowen ratio is typically less than 0.1 (Hsu 1998;Sadhuram et al 2001) because latent heat is the primary response of the ocean surface to solar heating. Different heat capacities of land and ocean also influence the amount of energy available for the diurnal cycle at a given time of the day but we neglect this effect here for the sake of simplicity.…”

Section: B Diurnal Cycle Forcing Bowen Ratio and Galilean Transformentioning

confidence: 99%

Simple Multicloud Models for the Diurnal Cycle of Tropical Precipitation. Part II: The Continental Regime

Frenkel

Khouider

Majda

2011

Journal of the Atmospheric Sciences

View full text Add to dashboard Cite

The variation of precipitation over land due to the diurnal cycle of solar heating is examined here in the context of a simple multicloud model for tropical convection with bulk atmospheric boundary layer (ABL) dynamics. The model utilizes three cloud types (congestus, deep, and stratiform) that are believed to characterize organized tropical convection based on the first two baroclinic modes of vertical structure in the free troposphere, coupled to the ABL through full bulk boundary layer (FBBL) dynamics, that allow a careful separation between sensible and latent heat surface fluxes. In a land parameter regime, characterized by a strong inversion profile, a large Bowen ratio of 0.4, and active mixing of sensible heat due to cumulus entrainment and downdraft fluxes at the top of the ABL, the model supports a stable 1-day periodic solution that is characterized by a pronounced (7 K day 21 ) afternoon peak in precipitation consistent with observations of tropical precipitation over continental regions. The current study suggests a division of the diurnal cycle of precipitation over land into a cycle of five phases: 1) an overnight phase of a radiative-convective equilibrium (RCE) state between 2000 and 0600 LST; 2) an early morning CAPE buildup accompanied by a sudden rise in precipitation that quickly dries the middle troposphere occurs between 0600 and roughly 1000 LST; 3) a moistening phase between roughly 1000 and 1600 LST; 4) a phase of maximum precipitation between 1600 and 1800 LST that dries the middle troposphere and quickly consumes CAPE; and 5) a rapid remoistening phase that restores the moisture level to sustain the overnight RCE precipitation and connects to phase 1 in the cycle. Sensitivity tests in the model confirm that the late afternoon precipitation maximum over land depends crucially on a strong inversion, the large Bowen ratio, and the active mixing of sensible heat due to cumulus entrainment and downdraft fluxes at the top of the ABL.

show abstract

Comments on “On the Estimation of Overwater Bowen Ratio from Sea–Air Temperature Difference”*

Cited by 7 publications

References 4 publications

Simple Multicloud Models for the Diurnal Cycle of Tropical Precipitation. Part I: Formulation and the Case of the Tropical Oceans

Simple Multicloud Models for the Diurnal Cycle of Tropical Precipitation. Part I: Formulation and the Case of the Tropical Oceans

Uncertainty analysis of computational methods for deriving sensible heat flux values from scintillometer measurements

Simple Multicloud Models for the Diurnal Cycle of Tropical Precipitation. Part II: The Continental Regime

Contact Info

Product

Resources

About