scholarly journals Unrealistic Increases in Wind Speed Explain Reduced Eastern Pacific Heat Flux in Reanalyses

2018 ◽  
Vol 31 (8) ◽  
pp. 2981-2993
Author(s):  
Chunlei Liu ◽  
Richard P. Allan
Keyword(s):  
Heat Flux ◽  
Wind Speed ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Climate Model ◽  
Surface Flux ◽  
Eastern Pacific ◽  
Tropical Eastern Pacific ◽  
Flux Variability ◽  
Climate Model Simulations

Abstract Tropical eastern Pacific sea surface temperature plays a pivotal role in mechanisms that determine global mean surface temperature variability. In this study, the surface flux contribution to recent cooling of the tropical eastern Pacific is investigated using data from three atmospheric reanalyses with full assimilation of observations, an observation-based net surface energy flux reconstruction, and 15 atmosphere-only climate model simulations. For ERA-Interim, 78% of the decrease in net surface flux (−0.65 W m−2 yr−1 over 1988–2008) is explained by the latent heat flux variability. Latent heat flux variability differs between datasets, and this is investigated using a bulk formula. It is found that discrepancies in wind speed change explain contrasting latent heat flux trends across datasets. The significant increase in wind speed of 0.26 m s−1 decade−1 over the tropical eastern Pacific in ERA-Interim is not reproduced by satellite or buoy observations or atmosphere-only climate model simulations, casting questions on the reliability of reanalysis-based surface fluxes over the tropical eastern Pacific.

scholarly journals On the parameterization of turbulent fluxes over the tropical Eastern Pacific

2006 ◽  
Vol 6 (3) ◽  
pp. 5251-5268
Author(s):  
G. B. Raga ◽  
S. Abarca
Keyword(s):  
Heat Flux ◽  
Wind Speed ◽  
Latent Heat ◽  
Turbulent Fluxes ◽  
Heat Fluxes ◽  
Eastern Pacific ◽  
Specific Humidity ◽  
Horizontal Wind ◽  
High Wind ◽  
Tropical Eastern Pacific

Abstract. We present estimates of turbulent fluxes of heat and momentum derived from low level (~30 m) aircraft measurements over the tropical Eastern Pacific and provide empirical relationships that are valid under high wind speed conditions (up to 25 ms−1). The estimates of total momentum flux and turbulent kinetic energy can be represented very accurately (r2=0.99, when data are binned every 1 ms−1) by empirical fits with a linear and a cubic terms of the average horizontal wind speed. The latent heat flux shows a strong quadratic dependence on the horizontal wind speed and a linear relationship with the difference between the air specific humidity and the saturated specific humidity at the sea surface, explaining 96% of the variance. The estimated values were used to evaluate the performance of three currently used parameterizations of turbulence fluxes, varying in complexity and computational requirements. The comparisons with the two more complex parameterizations show good agreement between the observed and parameterized latent heat fluxes, with less agreement in the sensible heat fluxes, and one of them largely overestimating the momentum fluxes. A third, very simple parameterization shows a surprisingly good agreement of the sensible heat flux, while momentum fluxes are again overestimated and a poor agreement was observed for the latent heat flux (r2=0.62). The performance of all three parameterizations deteriorates significantly in the high wind speed regime (above 10–15 ms−1). The dataset obtained over the tropical Eastern Pacific allows us to derive empirical functions for the turbulent fluxes that are applicable from 1 to 25 ms−1, which can be introduced in meteorological models under high wind conditions.

Wind Speed, Surface Flux, and Convection Coupling from CYGNSS Data

2021 ◽  
Author(s):  
Eric Maloney ◽  
Hien Bui ◽  
Emily Riley Dellaripa ◽  
Bohar Singh
Keyword(s):  
Heat Flux ◽  
Wind Speed ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Surface Wind ◽  
Surface Flux ◽  
Surface Wind Speed ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Boreal Summer

<p>This study analyzes wind speed and surface latent heat flux anomalies from the Cyclone Global Navigation Satellite System (CYGNSS), aiming to understand the physical mechanisms regulating intraseasonal convection, particularly associated with the Madden-Julian oscillation (MJO). The importance of wind-driven surface flux variability for supporting east Pacific diurnal convective disturbances during boreal summer is also examined. An advantage of CYGNSS compared to other space-based datasets is that its surface wind speed retrievals have reduced attenuation by precipitation, thus providing improved information about the importance of wind-induced surface fluxes for the maintenance of convection. Consistent with previous studies from buoys, CYGNSS shows that enhanced MJO precipitation is associated with enhanced wind speeds, and that associated surface heat fluxes anomalies have a magnitude about 7%-12% of precipitation anomalies. Thus, latent heat flux anomalies are an important maintenance mechanism for MJO convection through the column moist static energy budget. A composite analysis during boreal summer over the eastern north Pacific also supports the idea that wind-induced surface flux is important for MJO maintenance there. We also show the surface fluxes help moisten the atmosphere in advance of diurnal convective disturbances that propagate offshore from the Colombian Coast during boreal summer, helping to sustain such convection.  </p>

scholarly journals On the parameterization of turbulent fluxes over the tropical Eastern Pacific

2007 ◽  
Vol 7 (3) ◽  
pp. 635-643 ◽  
Author(s):  
G. B. Raga ◽  
S. Abarca
Keyword(s):  
Heat Flux ◽  
Wind Speed ◽  
Latent Heat ◽  
Turbulent Fluxes ◽  
Heat Fluxes ◽  
Eastern Pacific ◽  
Specific Humidity ◽  
Horizontal Wind ◽  
High Wind ◽  
Tropical Eastern Pacific

Abstract. We present estimates of turbulent fluxes of heat and momentum derived from low level (~30 m) aircraft measurements over the tropical Eastern Pacific and provide empirical relationships that are valid under high wind speed conditions (up to 25 ms−1). The estimates of total momentum flux and turbulent kinetic energy can be represented very accurately (r2=0.99, when data are binned every 1 ms−1) by empirical fits with a linear and a cubic terms of the average horizontal wind speed. The latent heat flux shows a strong quadratic dependence on the horizontal wind speed and a linear relationship with the difference between the air specific humidity and the saturated specific humidity at the sea surface, explaining 96% of the variance. The estimated values were used to evaluate the performance of three currently used parameterizations of turbulence fluxes, varying in complexity and computational requirements. The comparisons with the two more complex parameterizations show good agreement between the observed and parameterized latent heat fluxes, with less agreement in the sensible heat fluxes, and one of them largely overestimating the momentum fluxes. A third, very simple parameterization shows a surprisingly good agreement of the sensible heat flux, while momentum fluxes are again overestimated and a poor agreement was observed for the latent heat flux (r2=0.62). The performance of all three parameterizations deteriorates significantly in the high wind speed regime (above 10–15 ms−1). The dataset obtained over the tropical Eastern Pacific allows us to derive empirical functions for the turbulent fluxes that are applicable from 1 to 25 ms−1, which can be introduced in meteorological models under high wind conditions.

Diurnal variation in surface latent heat flux and the effect of diurnal variability on the climatological latent heat flux over the tropical oceans

2021 ◽  
Author(s):  
Yunwei Yan ◽  
Lei Zhang ◽  
Xiangzhou Song ◽  
Guihua Wang ◽  
Changlin Chen
Keyword(s):  
Heat Flux ◽  
Wind Speed ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Warm Pool ◽  
Diurnal Variability ◽  
Tropical Oceans ◽  
Mean Wind Speed

AbstractDiurnal variation in surface latent heat flux (LHF) and the effects of diurnal variations in LHF-related variables on the climatological LHF are examined using observations from the Global Tropical Moored Buoy Array. The estimated amplitude of the climatological diurnal LHF over the Indo-Pacific warm pool and the equatorial Pacific and Atlantic cold tongues is remarkable, with maximum values exceeding 20.0 W m−2. Diurnal variability of sea surface skin temperature (SSTskin) is the primary contributor to the diurnal LHF amplitude. Because the diurnal SSTskin amplitude has an inverse relationship with surface wind speed over the tropical oceans, an inverse spatial pattern between the diurnal LHF amplitude and surface wind speed results. Resolving diurnal variations in the SSTskin and wind improves the estimate of the climatological LHF by properly capturing the daytime SSTskin and daily mean wind speed, respectively. The diurnal SSTskin-associated contribution is large over the warm pool and equatorial cold tongues where low wind speeds tend to cause strong diurnal SSTskin warming, while the magnitude associated with the diurnal winds is large over the highly dynamic environment of the Inter-Tropical Convergence Zone. The total diurnal contribution is about 9.0 W m−2 on average over the buoy sites. There appears to be a power function (linear) relationship between the diurnal SSTskin-associated (wind-associated) contribution and surface mean wind speed (wind speed enhancement from diurnal variability). The total contribution from diurnal variability can be estimated accurately from high-frequency surface wind measurements using these relationships.

The Moist Static Energy Budget of a Composite Tropical Intraseasonal Oscillation in a Climate Model

2009 ◽  
Vol 22 (3) ◽  
pp. 711-729 ◽  
Author(s):  
Eric D. Maloney
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Climate Model ◽  
Intraseasonal Variability ◽  
Lower Troposphere ◽  
Specific Humidity ◽  
Horizontal Advection ◽  
Moisture Advection ◽  
Static Energy

Abstract The intraseasonal moist static energy (MSE) budget is analyzed in a climate model that produces realistic eastward-propagating tropical intraseasonal wind and precipitation variability. Consistent with the recharge–discharge paradigm for tropical intraseasonal variability, a buildup of column-integrated MSE occurs within low-level easterly anomalies in advance of intraseasonal precipitation, and a discharge of MSE occurs during and after precipitation when westerly anomalies occur. The strongest MSE anomalies peak in the lower troposphere and are, primarily, regulated by specific humidity anomalies. The leading terms in the column-integrated intraseasonal MSE budget are horizontal advection and surface latent heat flux, where latent heat flux is dominated by the wind-driven component. Horizontal advection causes recharge (discharge) of MSE within regions of anomalous equatorial lower-tropospheric easterly (westerly) anomalies, with the meridional component of the moisture advection dominating the MSE budget near 850 hPa. Latent heat flux anomalies oppose the MSE tendency due to horizontal advection, making the recharge and discharge of column MSE more gradual than if horizontal advection were acting alone. This relationship has consequences for the time scale of intraseasonal variability in the model. Eddies dominate intraseasonal meridional moisture advection in the model. During periods of low-level intraseasonal easterly anomalies, eddy kinetic energy (EKE) is anomalously low due to a suppression of tropical synoptic-scale disturbances and other variability on time scales shorter than 20 days. Anomalous moistening of the equatorial lower troposphere occurs during intraseasonal easterly periods through suppression of eddy moisture advection between the equator and poleward latitudes. During intraseasonal westerly periods, EKE is enhanced, leading to anomalous drying of the equatorial lower troposphere through meridional advection. Given the importance of meridional moisture advection and wind-induced latent heat flux to the intraseasonal MSE budget, these findings suggest that to simulate realistic intraseasonal variability, climate models must have realistic basic-state distributions of lower-tropospheric zonal wind and specific humidity.

scholarly journals Satellite and Buoy Observations of Boreal Summer Intraseasonal Variability in the Tropical Northeast Pacific

2007 ◽  
Vol 135 (1) ◽  
pp. 3-19 ◽  
Author(s):  
Eric D. Maloney ◽  
Steven K. Esbensen
Keyword(s):  
Heat Flux ◽  
Wind Speed ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Intraseasonal Variability ◽  
Warm Pool ◽  
East Pacific ◽  
Pacific Warm Pool ◽  
Westerly Flow ◽  
Trmm Precipitation

Abstract Tropical intraseasonal variability in the eastern North Pacific during June–September of 2000–03 is analyzed using satellite and buoy observations. Quick Scatterometer ocean vector winds and the Tropical Rainfall Measuring Mission (TRMM) precipitation indicate that periods of anomalous surface westerly flow over the east Pacific warm pool during a summertime intraseasonal oscillation (ISO) life cycle are generally associated with an enhancement of convection to the east of 120°W. An exception is a narrow band of suppressed precipitation along 8°N that is associated with negative column-integrated precipitable water anomalies and anticyclonic vorticity anomalies. Periods of surface easterly anomalies are generally associated with suppressed convection to the east of 120°W. Summertime wind jets in the Gulfs of Tehuantepec and Papagayo exhibit heightened activity during periods of ISO easterly anomalies and suppressed convection. Strong variations in east Pacific warm pool wind speed occur in association with the summertime ISO. Anomalous ISO westerly flow is generally accompanied by enhanced wind speed to the east of 120°W, while anomalous easterly flow is associated with suppressed wind speed. Intraseasonal vector wind anomalies added to the climatological flow account for the bulk of the wind speed enhancement in the warm pool during the westerly phase, while the easterly phase shows strong contributions to the negative wind speed anomaly from both intraseasonal vector wind anomalies and suppressed synoptic-scale eddy activity. An analysis using Tropical Atmosphere Ocean buoys and TRMM precipitation suggests that wind–evaporation feedback is important for supporting summertime intraseasonal convection over the east Pacific warm pool. A statistically significant correlation of 0.6 between intraseasonal latent heat flux and precipitation occurs at the 12°N, 95°W buoy. Correlations between precipitation and latent heat flux at the 10°N, 95°W and 8°N, 95°W buoys are positive (0.4), but not statistically significant. Intraseasonal latent heat flux anomalies at all buoys are primarily wind induced. Consistent with the suppressed convection there during the ISO westerly phase, a negative but not statistically significant correlation (−0.3) occurs between precipitation and latent heat flux at the 8°N, 110°W buoy.

Satellite Estimates of Wind Speed and Latent Heat Flux over the Global Oceans

2003 ◽  
Vol 16 (4) ◽  
pp. 637-656 ◽  
Author(s):  
Abderrahim Bentamy ◽  
Kristina B. Katsaros ◽  
Alberto M. Mestas-Nuñez ◽  
William M. Drennan ◽  
Evan B. Forde ◽  
...  
Keyword(s):  
Heat Flux ◽  
Wind Speed ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Global Oceans

scholarly journals Propagating Subsurface Uncertainty to the Atmosphere Using Fully Coupled Stochastic Simulations

2011 ◽  
Vol 12 (4) ◽  
pp. 690-701 ◽  
Author(s):  
John L. Williams ◽  
Reed M. Maxwell
Keyword(s):  
Heat Flux ◽  
Soil Moisture ◽  
Wind Speed ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Hydrologic Model ◽  
Stochastic Simulations ◽  
Multiple Model ◽  
Conditional Monte Carlo ◽  
Fully Coupled

Abstract Feedbacks between the land surface and the atmosphere, manifested as mass and energy fluxes, are strongly correlated with soil moisture, making soil moisture an important factor in land–atmosphere interactions. It is shown that a reduction of the uncertainty in subsurface properties such as hydraulic conductivity (K) propagates into the atmosphere, resulting in a reduction in uncertainty in land–atmosphere feedbacks that yields more accurate atmospheric predictions. Using the fully coupled groundwater-to-atmosphere model ParFlow-WRF, which couples the hydrologic model ParFlow with the Weather Research and Forecasting (WRF) atmospheric model, responses in land–atmosphere feedbacks and wind patterns due to subsurface heterogeneity are simulated. Ensembles are generated by varying the spatial location of subsurface properties while maintaining the global statistics and correlation structure. This approach is common to the hydrologic sciences but uncommon in atmospheric simulations where ensemble forecasts are commonly generated with perturbed initial conditions or multiple model parameterizations. It is clearly shown that different realizations of K produce variation in soil moisture, latent heat flux, and wind for both point and domain-averaged quantities. Using a single random field to represent a control case, varying amounts of K data are sampled and subsurface data are incorporated into conditional Monte Carlo ensembles to show that the difference between the ensemble mean prediction and the control saturation, latent heat flux, and wind speed are reduced significantly via conditioning of K. By reducing uncertainty associated with land–atmosphere feedback mechanisms, uncertainty is also reduced in both spatially distributed and domain-averaged wind speed magnitudes, thus improving the ability to make more accurate forecasts, which is important for many applications such as wind energy.

Climate and Vegetation in the Middle East: Interannual Variability and Drought Feedbacks

2007 ◽  
Vol 20 (15) ◽  
pp. 3924-3941 ◽  
Author(s):  
Benjamin F. Zaitchik ◽  
Jason P. Evans ◽  
Roland A. Geerken ◽  
Ronald B. Smith
Keyword(s):  
Heat Flux ◽  
Interannual Variability ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Vegetation Index ◽  
Climate Model ◽  
Sensible Heat Flux ◽  
Radiation Balance ◽  
Turbulent Heat ◽  
Sensible Heat

Abstract The Euphrates Plain (EP) experiences large interannual variability in vegetation cover, especially in areas of marginal rain-fed agriculture. Vegetation in this region is primarily limited by available soil moisture, as determined by winter precipitation, spring precipitation, and air temperature. Satellite analyses indicate that the springtime normalized difference vegetation index (NDVI) is negatively correlated with surface albedo, and that interannual variability in albedo in the EP produces an estimated forcing on the radiation balance that peaks at 16.0 W m−2 in May. Simulations with a regional climate model indicate that surface energy fluxes during a drought year (1999) differed substantially from those during a year with normal precipitation (2003). These differences were geographically specific, with the EP exhibiting increased albedo and decreased sensible heat flux while the neighboring Zagros Plateau region showed no albedo effect, a large increase in sensible heat flux, and an offsetting reduction in latent heat flux. In both the EP and the Zagros there was a potential for positive feedbacks on temperature and drought in late spring, though the most likely feedback mechanisms differed between the two regions: in the EP surface brightening leads to cooling and reduced turbulent heat flux, while in the Zagros region reduced latent heat flux leads to warming and a deepening of the planetary boundary layer.

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