scholarly journals Intraseasonal Latent Heat Flux Based on Satellite Observations

2009 ◽  
Vol 22 (17) ◽  
pp. 4539-4556 ◽  
Author(s):  
Semyon A. Grodsky ◽  
Abderrahim Bentamy ◽  
James A. Carton ◽  
Rachel T. Pinker
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Mixed Layer ◽  
Heat Budget ◽  
Mixed Layer Depth ◽  
Intraseasonal Variability ◽  
Surface Fluxes ◽  
Tropical Region ◽  
Surprising Result

Abstract Weekly average satellite-based estimates of latent heat flux (LHTFL) are used to characterize spatial patterns and temporal variability in the intraseasonal band (periods shorter than 3 months). As expected, the major portion of intraseasonal variability of LHTFL is due to winds, but spatial variability of humidity and SST are also important. The strongest intraseasonal variability of LHTFL is observed at the midlatitudes. It weakens toward the equator, reflecting weak variance of intraseasonal winds at low latitudes. It also decreases at high latitudes, reflecting the effect of decreased SST and the related decrease of time-mean humidity difference between heights z = 10 m and z = 0 m. Within the midlatitude belts the intraseasonal variability of LHTFL is locally stronger (up to 50 W m−2) in regions of major SST fronts (like the Gulf Stream and Agulhas). Here it is forced by passing storms and is locally amplified by unstable air over warm SSTs. Although weaker in amplitude (but still significant), intraseasonal variability of LHTFL is observed in the tropical Indian and Pacific Oceans due to wind and humidity perturbations produced by the Madden–Julian oscillations. In this tropical region intraseasonal LHTFL and incoming solar radiation vary out of phase so that evaporation increases just below the convective clusters. Over much of the interior ocean where the surface heat flux dominates the ocean mixed layer heat budget, intraseasonal SST cools in response to anomalously strong upward intraseasonal LHTFL. This response varies geographically, in part because of geographic variations of mixed layer depth and the resulting variations in thermal inertia. In contrast, in the eastern tropical Pacific and Atlantic cold tongue regions intraseasonal SST and LHTFL are positively correlated. This surprising result occurs because in these equatorial upwelling areas SST is controlled by advection rather than by surface fluxes. Here LHTFL responds to rather than drives SST.

scholarly journals On the Growth and Decay of the Subtropical Dipole Mode in the South Atlantic

2011 ◽  
Vol 24 (21) ◽  
pp. 5538-5554 ◽  
Author(s):  
Yushi Morioka ◽  
Tomoki Tozuka ◽  
Toshio Yamagata
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Mixed Layer ◽  
General Circulation ◽  
Mixed Layer Depth ◽  
South Atlantic ◽  
The South ◽  
Layer Depth ◽  
Negative Pole

Abstract Using observational data and outputs from an ocean general circulation model, the growth and decay of the South Atlantic subtropical dipole (SASD) are studied. The SASD is the most dominant mode of interannual variability in the South Atlantic Ocean, and its sea surface temperature (SST) anomaly shows a dipole pattern that is oriented in the northeast–southwest direction. The positive (negative) pole develops because the warming of the mixed layer by the contribution from the climatological shortwave radiation is enhanced (suppressed) when the mixed layer is thinner (thicker) than normal. The mixed layer depth anomaly over the positive (negative) pole is due to the suppressed (enhanced) latent heat flux loss associated with the southward migration and strengthening of the subtropical high. During the decay phase, since the temperature difference between the mixed layer and the entrained water becomes anomalously large (small) as a result of the positive (negative) mixed layer temperature anomaly, the cooling of the mixed layer by the entrainment is enhanced (reduced). In addition, the cooling of the mixed layer by the contribution from the climatological latent heat flux is enhanced (suppressed) by the same thinner (thicker) mixed layer. This paper demonstrates the importance of taking into account the interannual variations of the mixed layer depth in discussing the growth and decay of SST anomalies associated with the SASD.

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.

scholarly journals Simulated Seasonal and Interannual Variability of the Mixed Layer Heat Budget in the Northern Indian Ocean*

2007 ◽  
Vol 20 (13) ◽  
pp. 3249-3268 ◽  
Author(s):  
Clémentde Boyer Montégut ◽  
Jérôme Vialard ◽  
S. S. C. Shenoi ◽  
D. Shankar ◽  
Fabien Durand ◽  
...  
Keyword(s):  
Heat Flux ◽  
Indian Ocean ◽  
Interannual Variability ◽  
Latent Heat Flux ◽  
Mixed Layer ◽  
Heat Budget ◽  
Northern Indian Ocean ◽  
Solar Heat ◽  
Mixed Layer Heat Budget ◽  
Solar Heat Flux

Abstract A global ocean general circulation model (OGCM) is used to investigate the mixed layer heat budget of the northern Indian Ocean (NIO). The model is validated against observations and shows fairly good agreement with mixed layer depth data in the NIO. The NIO has been separated into three subbasins: the western Arabian Sea (AS), the eastern AS, and the Bay of Bengal (BoB). This study reveals strong differences between the western and eastern AS heat budget, while the latter basin has similarities with the BoB. Interesting new results on seasonal time scales are shown. The penetration of solar heat flux needs to be taken into account for two reasons. First, an average of 28 W m−2 is lost beneath the mixed layer over the year. Second, the penetration of solar heat flux tends to reduce the effect of solar heat flux on the SST seasonal cycle in the AS because the seasons of strongest flux are also seasons with a thin mixed layer. This enhances the control of SST seasonal variability by latent heat flux. The impact of salinity on SST variability is demonstrated. Salinity stratification plays a clear role in maintaining a high winter SST in the BoB and eastern AS while not in the western AS. The presence of freshwater near the surface allows heat storage below the surface layer that can later be recovered by entrainment warming during winter cooling (with a winter contribution of +2.1°C in the BoB). On an interannual time scale, the eastern AS and BoB are strongly controlled by the winds through the latent heat flux anomalies. In the western AS, vertical processes, as well as horizontal advection, contribute significantly to SST interannual variability, and the wind is not the only factor controlling the heat flux forcing.

Evaluation of Two Land Surface Schemes Used in Terrains of Increasing Aridity in West Africa

2008 ◽  
Vol 9 (2) ◽  
pp. 173-193 ◽  
Author(s):  
D. Schüttemeyer ◽  
A. F. Moene ◽  
A. A. M. Holtslag ◽  
H. A. R. de Bruin
Keyword(s):  
Heat Flux ◽  
West Africa ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Land Surface ◽  
Sensible Heat Flux ◽  
Surface Fluxes ◽  
Semiarid Region ◽  
Canopy Conductance ◽  
Net Radiation

Abstract In this study different parameterizations for land surface models currently employed in meteorological models at ECMWF [Tiled ECMWF Surface Scheme for Exchange Processes over Land (TESSEL)] and NCEP (Noah) are evaluated for a semiarid region in Ghana, West Africa. Both schemes utilize the Jarvis–Stewart approach to calculate canopy conductance as the critical variable for partitioning the available energy into sensible and latent heat flux. Additionally, an approach within Noah is tested to calculate canopy conductance based on plant physiology (A-gs method), where the photosynthetic assimilation is coupled to the leaf stomatal conductance. All parameterizations were run offline for a seasonal cycle in 2002/03 using observations as forcings at two test sites. The two locations are in the humid tropical southern region and in the drier northern region. For the purpose of forcing and evaluation, a new set of data has been utilized to include surface fluxes obtained by scintillometry. The measurements include the rapid wet-to-dry transition after the wet season at both sites. As a general trend, it has been found that during the wet period of a season net radiation is described well by all parameterizations. During the drying process the errors in modeled net radiation increased at both sites. The models perform poorly in simulating soil heat fluxes with larger errors for TESSEL for both sites. The evolution in time for sensible heat flux and latent heat flux was tackled in different ways by the utilized parameterizations and sites with enhanced model performance for the more southern site. Soil moisture in the upper soil layers is modeled with small errors for the different parameterizations. Key adjustments for reducing net radiation during the dry period of a season are discussed. In particular, the ratio of roughness length of momentum and heat was found to be an important parameter, but will require seasonal adjustments.

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 A Diagnostic Model for Mixed Layer Depth Estimation with Application to Ocean Station P in the Northeast Pacific

2009 ◽  
Vol 39 (6) ◽  
pp. 1399-1415 ◽  
Author(s):  
Richard E. Thomson ◽  
Isaac V. Fine
Keyword(s):  
Heat Flux ◽  
Surface Temperature ◽  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Depth Estimation ◽  
Surface Fluxes ◽  
Late Winter ◽  
Diagnostic Model ◽  
Layer Depth ◽  
Northeast Pacific

Abstract This paper presents a simple diagnostic model for estimating mixed layer depth based solely on the one-dimensional heat balance equation, the surface heat flux, and the sea surface temperature. The surface fluxes drive heating or cooling of the upper layer whereas the surface temperature acts as a “thermostat” that regulates the vertical extent of the layer. Daily mixed layer depth estimates from the diagnostic model (and two standard bulk mixed layer models) are compared with depths obtained from oceanic profiles collected during the 1956–80 Canadian Weathership program at Station P and more recent (2001–07) profiles from the vicinity of this station from Argo drifters. Summer mixed layer depths from the diagnostic model agree more closely with observed depths and are less sensitive to heat flux errors than those from bulk models. For the Weathership monitoring period, the root-mean-square difference between modeled and observed monthly mean mixed layer depths is ∼6 m for the diagnostic model and ∼10 m for the bulk models. The diagnostic model is simpler to apply than bulk models and sidesteps the need for wind data and turbulence parameterization required by these models. Mixed layer depths obtained from the diagnostic model using NCEP–NCAR reanalysis data reveal that—contrary to reports for late winter—there has been no significant trend in the summer mixed layer depth in the central northeast Pacific over the past 52 yr.

In Situ Observations of Madden–Julian Oscillation Mixed Layer Dynamics in the Indian and Western Pacific Oceans

2012 ◽  
Vol 25 (7) ◽  
pp. 2306-2328 ◽  
Author(s):  
Kyla Drushka ◽  
Janet Sprintall ◽  
Sarah T. Gille ◽  
Susan Wijffels
Keyword(s):  
Heat Flux ◽  
Indian Ocean ◽  
Mixed Layer ◽  
Heat Budget ◽  
Mixed Layer Depth ◽  
Layer Depth ◽  
Temperature Variations ◽  
Central Indian Ocean ◽  
Mixed Layer Temperature

Abstract The boreal winter response of the ocean mixed layer to the Madden–Julian oscillation (MJO) in the Indo-Pacific region is determined using in situ observations from the Argo profiling float dataset. Composite averages over numerous events reveal that the MJO forces systematic variations in mixed layer depth and temperature throughout the domain. Strong MJO mixed layer depth anomalies (>15 m peak to peak) are observed in the central Indian Ocean and in the far western Pacific Ocean. The strongest mixed layer temperature variations (>0.6°C peak to peak) are found in the central Indian Ocean and in the region between northwest Australia and Java. A heat budget analysis is used to evaluate which processes are responsible for mixed layer temperature variations at MJO time scales. Though uncertainties in the heat budget are on the same order as the temperature trend, the analysis nonetheless demonstrates that mixed layer temperature variations associated with the canonical MJO are driven largely by anomalous net surface heat flux. Net heat flux is dominated by anomalies in shortwave and latent heat fluxes, the relative importance of which varies between active and suppressed MJO conditions. Additionally, rapid deepening of the mixed layer in the central Indian Ocean during the onset of active MJO conditions induces significant basin-wide entrainment cooling. In the central equatorial Indian Ocean, MJO-induced variations in mixed layer depth can modulate net surface heat flux, and therefore mixed layer temperature variations, by up to ~40%. This highlights the importance of correctly representing intraseasonal mixed layer depth variations in climate models in order to accurately simulate mixed layer temperature, and thus air–sea interaction, associated with the MJO.

scholarly journals Evolving Land–Atmosphere Interactions over North America from CMIP5 Simulations

2013 ◽  
Vol 26 (19) ◽  
pp. 7313-7327 ◽  
Author(s):  
Paul A. Dirmeyer ◽  
Yan Jin ◽  
Bohar Singh ◽  
Xiaoqin Yan
Keyword(s):  
Heat Flux ◽  
North America ◽  
Boundary Layers ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Forced Response ◽  
Surface Fluxes ◽  
Future Climate Change ◽  
Cloud Base ◽  
Climate Change Scenarios

Abstract Long-term changes in land–atmosphere interactions during spring and summer are examined over North America. A suite of models from phase 5 of the Coupled Model Intercomparison Project simulating preindustrial, historical, and severe future climate change scenarios are examined for changes in soil moisture, surface fluxes, atmospheric boundary layer characteristics, and metrics of land–atmosphere coupling. Simulations of changes from preindustrial to modern conditions show warming brings stronger surface fluxes at high latitudes, while subtropical regions of North America respond with drier conditions. There is a clear anthropogenic aerosol response in midlatitudes that reduces surface radiation and heat fluxes, leading to shallower boundary layers and lower cloud base. Over the Great Plains, the signal does not reflect a purely radiatively forced response, showing evidence that the expansion of agriculture may have offset the aerosol impacts on the surface energy and water cycle. Future changes show soils are projected to dry across North America, even though precipitation increases north of a line that retreats poleward from spring to summer. Latent heat flux also has a north–south dipole of change, increasing north and decreasing south of a line that also moves northward with the changing season. Metrics of land–atmosphere feedback increase over most of the continent but are strongest where latent heat flux increases in the same location and season where precipitation decreases. Combined with broadly elevated cloud bases and deeper boundary layers, land–atmosphere interactions are projected to become more important in the future with possible consequences for seasonal climate prediction.

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