scholarly journals ROLE OF LAND SURFACE CONDITIONS ON THE MONSOON ONSET IN SOUTHEAST ASIA

2007 ◽  
Vol 51 ◽  
pp. 217-222
Author(s):  
Koji DAIRAKU
Keyword(s):  
Southeast Asia ◽  
Land Surface ◽  
Monsoon Onset ◽  
Surface Conditions

Role of Antecedent Land Surface Conditions in Warm Season Precipitation over Northwestern Mexico

2007 ◽  
Vol 20 (9) ◽  
pp. 1774-1791 ◽  
Author(s):  
Chunmei Zhu ◽  
Tereza Cavazos ◽  
Dennis P. Lettenmaier
Keyword(s):  
Land Surface ◽  
Thermal Condition ◽  
Large Scale ◽  
Positive Relationship ◽  
Winter Precipitation ◽  
Monsoon Onset ◽  
Surface Conditions ◽  
Nw Mexico ◽  
Northwestern Mexico

Abstract The role of antecedent land surface conditions including precipitation (P), surface skin temperature (Ts), soil moisture (Sm), and snow water equivalent (SWE) anomalies on the onset and intensity of the monsoon during the 1950–99 period in the core of the North American monsoon system (NAMS) region in northwestern Mexico (termed MSa here) is explored. A statistically significant positive relationship is found between monsoon onset date in MSa and previous winter precipitation in the southwestern United States (SW) and northwestern (NW) Mexico, and winter SWE in the southern Rocky Mountains. The linkages are strong during the 1960s–80s and weak otherwise, which is a much shorter period than had been found previously for an SW target area termed monsoon west (MW). In the MW study, the following land surface feedback hypothesis was proposed: more winter P and SWE lead to more spring Sm, hence lower spring and early summer Ts, which induce a weaker onset of the NAMS. This hypothesis broke down in MW due to the small contribution of land surface memory to surface thermal condition, and hence to monsoon strength. The same hypothesis is in this work for MSa by examining three links. First, it is found that in May not only the total column, but also the near-surface Sm, in both SW and NW Mexico have memory from the previous winter precipitation. The spring Sm anomalies correlate negatively with Ts anomalies over most of the continental United States and Mexico except for the desert region of SW and NW Mexico. The monsoon onset is negatively correlated with May Ts over an area roughly consisting of New Mexico and some adjacent areas, suggesting that antecedent land surface conditions may influence the premonsoon surface thermal condition, which then affects monsoon onset. The monsoon-driving force concept that states that the strength of the monsoon should be related to premonsoon land–sea surface temperature contrasts is also confirmed. The confirmation of this concept shows that late monsoon years are associated with colder land and warmer adjacent ocean than early monsoon years. In addition to the apparent land surface feedback, a strong positive relationship between May Ts anomalies and the large-scale midtropospheric circulation (Z500) anomalies is found, which suggests that large-scale circulation may play a strong (possibly more important than land feedback) role in modulating the monsoon onset.

scholarly journals Surface heterogeneity impacts on boundary layer dynamics via energy balance partitioning

2010 ◽  
Vol 10 (7) ◽  
pp. 17815-17851 ◽  
Author(s):  
N. A. Brunsell ◽  
D. B. Mechem ◽  
M. C. Anderson
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Land Surface ◽  
Surface Heterogeneity ◽  
Length Scales ◽  
Surface Conditions ◽  
Boundary Layer Dynamics

Abstract. The role of land-atmosphere interactions under heterogeneous surface conditions is investigated in order to identify mechanisms responsible for altering surface heat and moisture fluxes. Twelve coupled land surface – large eddy simulation scenarios with four different length scales of surface variability under three different horizontal wind speeds are used in the analysis. The base case uses Landsat ETM imagery over the Cloud Land Surface Interaction Campaign (CLASIC) field site for 3 June 2007. Using wavelets, the surface fields are band-pass filtered in order to maintain the spatial mean and variances to length scales of 200 m, 1600 m, and 12.8 km as lower boundary conditions to the model. The simulations exhibit little variation in net radiation. Rather, a change in the partitioning of the surface energy between sensible and latent heat flux is responsible for differences in boundary layer dynamics. The sensible heat flux is dominant for intermediate surface length scales. For smaller and larger scales of surface heterogeneity, which can be viewed as being more homogeneous, the latent heat flux becomes increasingly important. The results reflect a general decrease of the Bowen ratio as the surface conditions transition from heterogeneous to homogeneous. Air temperature is less sensitive to surface heterogeneity than water vapor, which implies that the role of surface heterogeneity in modifying the local temperature gradients in order to maximize convective heat fluxes. More homogeneous surface conditions, on the other hand, tend to maximize latent heat flux. Scalar vertical profiles respond predictably to the partitioning of surface energy. Fourier spectra of the vertical wind speed, air temperature and specific humidity (w, T and q) and associated cospectra (w'T', w'q' and T'q'), however, are insensitive to the length scale of surface heterogeneity, but the near surface spectra are sensitive to the mean wind speed.

scholarly journals Role of climate forecasts and initial land-surface conditions in developing operational streamflow and soil moisture forecasts in a rainfall-runoff regime: skill assessment

2012 ◽  
Vol 9 (4) ◽  
pp. 5225-5260 ◽  
Author(s):  
T. Sinha ◽  
A. Sankarasubramanian
Keyword(s):  
Land Surface ◽  
Lead Time ◽  
Rainfall Runoff ◽  
Surface Conditions ◽  
Climate Forecasts ◽  
Monthly Streamflow ◽  
Streamflow Forecasts ◽  
Runoff Regime ◽  
Seasonal Streamflow

Abstract. Skillful seasonal streamflow forecasts obtained from climate and land surface conditions could significantly improve water and energy management. Since climate forecasts are updated on monthly basis, we evaluate the potential in developing operational monthly streamflow forecasts on a continuous basis throughout the year. Further, basins in the rainfall-runoff regime critically depend on the forecasted precipitation in the upcoming months as opposed to snowmelt regimes where initial hydrological conditions (IHC) play a critical role. The goal of this study is to quantify the role of monthly updated precipitation forecasts and IHC in forecasting 6-month lead monthly streamflow for a rainfall-runoff mechanism dominated basin – Apalachicola River at Chattahoochee, FL. The Variable Infiltration Capacity (VIC) land surface model is implemented with two forcings: (a) monthly updated precipitation forecasts from ECHAM4.5 Atmospheric General Circulation Model (AGCM) forced with sea surface temperature forecasts and (b) daily climatological ensemble. The difference in skill between the above two quantifies the improvements that could be attainable using the AGCM forecasts. Monthly retrospective streamflow forecasts are developed from 1981 to 2010 and streamflow forecasts estimated from the VIC model are also compared with those predicted by using the principal component regression (PCR) model. Mean square error (MSE) in predicting monthly streamflow using the above VIC model are compared with the MSE of streamflow climatology under ENSO conditions as well as under normal years. Results indicate that VIC forecasts, at 1–2 month lead time, obtained using ECHAM4.5 are significantly better than VIC forecasts obtained using climatological ensemble over all the seasons except forecasts issued in fall and the PCR models perform better during the fall months. Over longer lead times (3–6 months), VIC forecasts derived using ECHAM4.5 forcings alone performed better compared to the MSE of streamflow climatology during winter and spring seasons. During ENSO years, streamflow forecasts exhibit better skill even up to six month lead time. Comparison of the seasonal soil moisture forecasts developed using ECHAM4.5 forcings with seasonal streamflow also show significant skill at 1–3 month lead time over the all four seasons.

scholarly journals Surface heterogeneity impacts on boundary layer dynamics via energy balance partitioning

2011 ◽  
Vol 11 (7) ◽  
pp. 3403-3416 ◽  
Author(s):  
N. A. Brunsell ◽  
D. B. Mechem ◽  
M. C. Anderson
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Wind Speed ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Land Surface ◽  
Surface Heterogeneity ◽  
Length Scales ◽  
Surface Conditions

Abstract. The role of land-atmosphere interactions under heterogeneous surface conditions is investigated in order to identify mechanisms responsible for altering surface heat and moisture fluxes. Twelve coupled land surface – large eddy simulation scenarios with four different length scales of surface variability under three different horizontal wind speeds are used in the analysis. The base case uses Landsat ETM imagery over the Cloud Land Surface Interaction Campaign (CLASIC) field site for 3 June 2007. Using wavelets, the surface fields are band-pass filtered in order to maintain the spatial mean and variances to length scales of 200 m, 1600 m, and 12.8 km as lower boundary conditions to the model (approximately 0.25, 1.2 and 9.5 times boundary layer height). The simulations exhibit little variation in net radiation. Rather, there is a pronounced change in the partitioning of the surface energy between sensible and latent heat flux. The sensible heat flux is dominant for intermediate surface length scales. For smaller and larger scales of surface heterogeneity, which can be viewed as being more homogeneous, the latent heat flux becomes increasingly important. The simulations showed approximately 50 Wm−2 difference in the spatially averaged latent heat flux. The results reflect a general decrease of the Bowen ratio as the surface conditions transition from heterogeneous to homogeneous. Air temperature is less sensitive to variations in surface heterogeneity than water vapor, which implies that the role of surface heterogeneity may be to maximize convective heat fluxes through modifying and maintaining local temperature gradients. More homogeneous surface conditions (i.e. smaller length scales), on the other hand, tend to maximize latent heat flux. The intermediate scale (1600 m) this does not hold, and is a more complicated interaction of scales. Scalar vertical profiles respond predictably to the partitioning of surface energy. Fourier spectra of the vertical wind speed, air temperature and specific humidity (w~, T~ and q~) and associated cospectra (w~T~, w~q~ and T~q~), however, are insensitive to the length scale of surface heterogeneity, but the near surface spectra are sensitive to the mean wind speed.

scholarly journals Numerical Simulations of the Role of Land Surface Conditions in the Evolution and Structure of Summertime Thunderstorms over a Flat Highland

2008 ◽  
Vol 136 (1) ◽  
pp. 173-188 ◽  
Author(s):  
Hiroyuki Yamada
Keyword(s):  
Numerical Simulations ◽  
Land Surface ◽  
Initial Conditions ◽  
Precipitation Process ◽  
Atmospheric Conditions ◽  
Surface Conditions ◽  
Central Tibetan Plateau ◽  
Vegetation Activity ◽  
Cloud Evolution

Abstract Numerical simulations of summertime thunderstorms over a flat highland (4700 m MSL), assuming the central Tibetan Plateau, were conducted with the use of a cloud-resolving nonhydrostatic model. This study was aimed at clarifying the role of land surface conditions, such as soil moisture and vegetation activity, in the evolution and structure of airmass thunderstorms over the plateau. Two simulations with cyclic lateral boundaries and different surfaces of a dry or wet land were initialized using a unique vertical atmospheric profile at dawn. These initial conditions assume the real atmospheric conditions in two periods of the 1998 summer monsoon, which are characterized by a dry or wet surface. The results of the two experiments were used to examine the contrasting features between the two experiments arising from the different surface conditions. The simulations reproduced differences in the convective structure, the conditions of the subcloud layer, and the evaporation rate of precipitation within this layer. These resulted from different surface-heating processes and were supported by the observational evidence clarified in a previous study. Moreover, the simulations also reproduced the cell broadening occurring in both the boundary and cloud layers and different precipitation processes dependent on the updraft strength. The evidence was partly supported by additional analyses of observational data. This study, therefore, demonstrates a significant effect of the plateau surface upon the cloud evolution and the precipitation process.

scholarly journals Rhinocerotidae from the early Miocene of the Negev (Israel) and implications for the dispersal of early Neogene rhinoceroses

2021 ◽  
pp. 1-12
Author(s):  
Luca Pandolfi ◽  
Ran Calvo ◽  
Ari Grossman ◽  
Rivka Rabinovich
Keyword(s):  
Southeast Asia ◽  
South Asian ◽  
North Africa ◽  
Range Expansion ◽  
New Records ◽  
Ct Scanning ◽  
Early Miocene ◽  
Early Neogene ◽  
Postcranial Remains

Abstract A revision of the rhinocerotid material from the Negev (Israel), dating back to the early Miocene (MN3 in the European Mammal Biochronology), highlights the presence of Brachypotherium and a taxon close to Gaindatherium in the Levantine corridor. A juvenile mandible, investigated using CT scanning, displays morphologically distinct characters consistent with Brachypotherium cf. B. snowi rather than with other Eurasian representatives of this genus. Some postcranial remains from the Negev, such as a humerus, display features that distinguish it among Miocene taxa. We attribute these postcrania to cf. Gaindatherium sp., a taxon never recorded outside the Siwaliks until now. This taxon dispersed into the Levantine region during the late early Miocene, following a pattern similar to other South Asian taxa. Brachypotherium cf. B. snowi probably occurred in the Levantine region and then in North Africa during the early Miocene because its remains are known from slightly younger localities such as Moghara (Egypt) and Jebel Zelten (Libya). The occurrence cf. Gaindatherium sp. represents a previously unrecorded range expansion out of Southeast Asia. These new records demonstrate the paleogeographic importance of the Levantine region showcasing the complex role of the Levantine corridor in intercontinental dispersals between Asia and Europe as well as Eurasia and Africa.

Role of Land-Surface Changes in Arctic Summer Warming

Science ◽  
2005 ◽  
Vol 310 (5748) ◽  
pp. 657-660 ◽  
Author(s):  
F. S. Chapin
Keyword(s):  
Land Surface ◽  
Summer Warming ◽  
Arctic Summer ◽  
Surface Changes
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