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 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 Understanding the Impacts of Soil Moisture Initial Conditions on NWP in the Context of Land–Atmosphere Coupling

2019 ◽  
Vol 20 (5) ◽  
pp. 793-819 ◽  
Author(s):  
Joseph A. Santanello Jr. ◽  
Patricia Lawston ◽  
Sujay Kumar ◽  
Eli Dennis
Keyword(s):  
Soil Moisture ◽  
High Resolution ◽  
Land Surface ◽  
Initial Conditions ◽  
Land Surface Model ◽  
Surface Model ◽  
Coupled Models ◽  
Wide Range ◽  
Soil Moisture Initialization

Abstract The role of soil moisture in NWP has gained more attention in recent years, as studies have demonstrated impacts of land surface states on ambient weather from diurnal to seasonal scales. However, soil moisture initialization approaches in coupled models remain quite diverse in terms of their complexity and observational roots, while assessment using bulk forecast statistics can be simplistic and misleading. In this study, a suite of soil moisture initialization approaches is used to generate short-term coupled forecasts over the U.S. Southern Great Plains using NASA’s Land Information System (LIS) and NASA Unified WRF (NU-WRF) modeling systems. This includes a wide range of currently used initialization approaches, including soil moisture derived from “off the shelf” products such as atmospheric models and land data assimilation systems, high-resolution land surface model spinups, and satellite-based soil moisture products from SMAP. Results indicate that the spread across initialization approaches can be quite large in terms of soil moisture conditions and spatial resolution, and that SMAP performs well in terms of heterogeneity and temporal dynamics when compared against high-resolution land surface model and in situ soil moisture estimates. Case studies are analyzed using the local land–atmosphere coupling (LoCo) framework that relies on integrated assessment of soil moisture, surface flux, boundary layer, and ambient weather, with results highlighting the critical role of inherent model background biases. In addition, simultaneous assessment of land versus atmospheric initial conditions in an integrated, process-level fashion can help address the question of whether improvements in traditional NWP verification statistics are achieved for the right reasons.

scholarly journals Multiple steady-states in the terrestrial atmosphere-biosphere system: a result of a discrete vegetation classification?

2007 ◽  
Vol 4 (5) ◽  
pp. 707-714 ◽  
Author(s):  
A. Kleidon ◽  
K. Fraedrich ◽  
C. Low
Keyword(s):  
Land Surface ◽  
Initial Conditions ◽  
Steady States ◽  
Multiple Steady States ◽  
Atmospheric Conditions ◽  
Vegetation Productivity ◽  
Positive Feedbacks ◽  
Terrestrial Atmosphere ◽  
The Difference ◽  
Global Vegetation

Abstract. Multiple steady states in the atmosphere-biosphere system can arise as a consequence of interactions and positive feedbacks. While atmospheric conditions affect vegetation productivity in terms of available light, water, and heat, different levels of vegetation productivity can result in differing energy- and water partitioning at the land surface, thereby leading to different atmospheric conditions. Here we investigate the emergence of multiple steady states in the terrestrial atmosphere-biosphere system and focus on the role of how vegetation is represented in the model: (i) in terms of a few, discrete vegetation classes, or (ii) a continuous representation. We then conduct sensitivity simulations with respect to initial conditions and to the number of discrete vegetation classes in order to investigate the emergence of multiple steady states. We find that multiple steady states occur in our model only if vegetation is represented by a few vegetation classes. With an increased number of classes, the difference between the number of multiple steady states diminishes, and disappears completely in our model when vegetation is represented by 8 classes or more. Despite the convergence of the multiple steady states into a single one, the resulting climate-vegetation state is nevertheless less productive when compared to the emerging state associated with the continuous vegetation parameterization. We conclude from these results that the representation of vegetation in terms of a few, discrete vegetation classes can result (a) in an artificial emergence of multiple steady states and (b) in a underestimation of vegetation productivity. Both of these aspects are important limitations to be considered when global vegetation-atmosphere models are to be applied to topics of global change.

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 Role of warm ocean conditions and the MJO in the genesis and intensification of extremely severe cyclone Fani

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Vineet Kumar Singh ◽  
M. K. Roxy ◽  
Medha Deshpande
Keyword(s):  
Wind Speed ◽  
Initial Conditions ◽  
Monsoon Season ◽  
Ocean Surface ◽  
Rapid Intensification ◽  
Atmospheric Conditions ◽  
Large Area ◽  
Record Time ◽  
Time Period

AbstractCyclone Fani, in April 2019, was the strongest pre-monsoon cyclone to form in the Bay of Bengal after 1994. It underwent rapid intensification and intensified quickly to an extremely severe cyclone. It maintained a wind speed of ≥ 51 m s−1 (≥ 100 knots) for a record time period of 36 h. The total lifespan of the cyclone was double than the climatological lifespan. Also, the duration of the cyclone in its extremely severe phase and the accumulated cyclone energy were significantly larger than the climatological records for the pre-monsoon season. In the current study, we investigate the ocean-atmospheric conditions that led to its genesis, rapid intensification and long lifespan. Our analysis shows that the Madden Julian Oscillation and anomalous high sea surface temperatures provided conducive dynamic and thermodynamic conditions for the genesis of cyclone Fani, despite forming very close to the equator where cyclogenesis is generally unlikely. Further, favourable ocean subsurface conditions and the presence of a warm core eddy in the region led to its rapid intensification to an extremely severe cyclone. A large area of warm ocean surface and subsurface temperatures aided the cyclone to maintain very high wind speed for a record time period. The vital role of the ocean surface and the subsurface in the genesis and the intensification highlights the need to efficiently incorporate ocean initial conditions (surface and sub-surface) and ocean–atmosphere coupling in the operational cyclone forecasting framework.

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 Multiple steady-states in the terrestrial atmosphere-biosphere system: a result of a discrete vegetation classification?

2007 ◽  
Vol 4 (1) ◽  
pp. 687-705 ◽  
Author(s):  
A. Kleidon ◽  
K. Fraedrich ◽  
C. Low
Keyword(s):  
Land Surface ◽  
Initial Conditions ◽  
Steady States ◽  
Multiple Steady States ◽  
Atmospheric Conditions ◽  
Vegetation Productivity ◽  
Positive Feedbacks ◽  
Terrestrial Atmosphere ◽  
The Difference ◽  
Global Vegetation

Abstract. Multiple steady states in the atmosphere-biosphere system can arise as a consequence of interactions and positive feedbacks. While atmospheric conditions affect vegetation productivity in terms of available light, water, and heat, different levels of vegetation productivity can result in differing energy- and water partitioning at the land surface, thereby leading to different atmospheric conditions. Here we investigate the emergence of multiple steady states in the terrestrial atmosphere-biosphere system and focus on the role of how vegetation is represented in the model: (i) in terms of a few, discrete vegetation classes, or (ii) a continuous representation. We then conduct sensitivity simulations with respect to initial conditions and to the number of discrete vegetation classes in order to investigate the emergence of multiple steady states. We find that multiple steady states occur in our model only if vegetation is represented by a few vegetation classes. With an increased number of classes, the difference between the number of multiple steady states diminishes, and disappears completely in our model when vegetation is represented by 8 classes or more. Despite the convergence of the multiple steady states into a single one, the resulting climate-vegetation state is nevertheless less productive when compared to the emerging state associated with the continuous vegetation parameterization. We conclude from these results that the representation of vegetation in terms of a few, discrete vegetation classes can result (a) in an artificial emergence of multiple steady states and (b) in a underestimation of vegetation productivity. Both of these aspects are important limitations to be considered when global vegetation-atmosphere models are to be applied to topics of global change.

Legacy effects of climate overshoot scenarios in permafrost-affected regions

2021 ◽  
Author(s):  
Philipp de Vrese ◽  
Victor Brovkin
Keyword(s):  
Land Surface ◽  
Net Primary Productivity ◽  
Initial Conditions ◽  
Organic Matter Content ◽  
Steady States ◽  
The Arctic ◽  
Atmospheric Conditions ◽  
Max Planck ◽  
Climate Target

<p>Difficulties to quickly reduce carbon emissions to levels compatible with the long-term goal of the Paris Agreement increase the likelihood of scenarios that temporarily overshoot the respective climate targets. We used simulations with JSBACH, the land surface component of the Max-Planck-Institute for Meteorology’s Earth system model MPI-ESM1.2 to investigate the long-term response of the terrestrial Arctic to climate stabilization at such a climate target. In particular, we seek to answer the question whether the state of permafrost-affected soils and the Arctic carbon cycle could converge to different equilibria depending on the climate trajectory that precedes climate stabilization at 1.5°C above pre-industrial levels. To this end, we compare simulations that are forced with the same non-transient atmospheric conditions – corresponding to the 1.5°C-target --, but started from different initial conditions. One simulation was initialized with the conditions before and one simulation with the conditions after a temperature overshoot which follows SSP5-8.5 until the year 2100 subsequent to which the atmospheric conditions are reversed to the 1.5°C-target. Our results reveal that feedbacks between water-, energy- and carbon cycles allow for path-dependent steady-states in permafrost-affected regions. These depend on the soil organic matter content at the point of climate stabilization, which is significantly affected by the soil carbon loss resulting from overshooting the climate target. Here, the simulated steady-states do not only differ with respect to the amount of carbon stored in the frozen fraction of the soil, but also with respect to soil temperatures, the soil water content and even net primary productivity and soil respiration.</p>

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.

Sign in / Sign up

Export Citation Format

Share Document