Control Simulation Research Articles

Atmospheric Circulation in the Furnas Reservoir Region, MG: Sensitivity Experiments with RegCM5 in Convection-Permitting Mode

In the 1950s, the Furnas reservoir was created, an artificial lake surrounded by hills, for the operation of the Furnas Hydroelectric Power Plant in southeastern Brazil. Along the shores of the Furnas reservoir, there are no meteorological stations, and only three are found at a distance greater than 10 km from the reservoir, which makes it challenging to assess the lake's influence on the local climate. To address this issue, the Regional Climate Model version 5 (RegCM5) was run in convection-permitting (CP) mode for two months, with a horizontal resolution of 1 km, to investigate the near-surface atmospheric circulation patterns around the reservoir. Three numerical experiments were conducted using RegCM5-CP nested in ERA5 reanalysis: a control simulation (CTRL), an experiment where the topography was assumed to be flat throughout the domain (expTOPO), and an experiment where the water body was replaced by vegetation (expVEG). The first month of simulation in each experiment was excluded from the analysis as it was considered a spin-up period. RegCM5-CP has good performance in simulating the diurnal cycle of the 2-m air temperature and reasonable performance for the 10-m wind intensity compared to observed data from three meteorological stations in the domain of simulation (but distant from the reservoir shore). Despite the geographic complexity of the Furnas reservoir, the experiments revealed coupling between lake and valley breezes during the daytime and land and mountain breezes during nighttime in different segments of the reservoir, such as in Guapé (near the dam). However, mountain-valley breezes are more dominant.

Land‐Locked Convection as a Barrier to MJO Propagation Across the Maritime Continent

AbstractLarge‐scale convection associated with the Madden‐Julian Oscillation (MJO) initiates over the Indian Ocean and propagates eastward across the Maritime Continent (MC). Over the MC, MJO events are generally weakened due to complex interactions between the large‐scale MJO and the MC landmass. The MC barrier effect is responsible for the dissipation of 40%–50% of observed MJO events and is often exaggerated in weather and climate models. We examine how MJO propagation over the MC is affected by two aspects of the MC—its land‐sea contrast and its terrain. To isolate the effects of mountains and land‐sea contrast on MJO propagation, we conduct three high‐resolution coupled atmosphere‐ocean model experiments: (a) control simulation (CTRL) of the 2011 November–December MJO event, (b) flattened terrain without MC mountains (FLAT), and (c) no‐land simulation (WATER) in which the MC islands are replaced with 50 m deep ocean. CTRL captures the general properties of the diurnal cycle of precipitation and MJO propagation across the MC. The WATER simulation produces a more intense and smoother‐propagating MJO compared with that of CTRL. In contrast, the convergence of sea breezes in the FLAT simulation produces much more organized convection and precipitation far inland than in CTRL, which results in a stronger barrier effect to MJO propagation. The land‐sea contrast induced land‐locked convection weakens the MJO's convective organization. The land‐locked convective systems over land in FLAT are more intense, grow larger, and last longer, which is more detrimental to MJO propagation over the MC, than the mountains that are present in CTRL.

Evaluating the Role of Land Surface Moisture in Generating Asymmetrical Precipitation during the Landfall of Hurricane Florence (2018)

This study focuses on the role of land surface moisture in generating asymmetrical precipitation surrounding a nearly stationary Hurricane Florence (2018) during landfall. Previous idealized modeling studies have suggested that atmospheric stability varies surrounding a tropical cyclone (TC) during landfall, with the atmosphere destabilizing off-shore and stabilizing on-shore. However, this finding has not been studied using a real modeling framework. Here, we produce high-resolution numerical simulations to examine the variations in precipitation and atmospheric stability surrounding Hurricane Florence. In addition to a control simulation (CTRL), two additional simulations are performed by altering the land surface cover to be moister (WETX) or drier (DRYX) compared with the CTRL. In the experiment, the altered land surface affects the equivalent potential temperature within the boundary layer. Due to changes in moisture, there are consistent but minor impacts on the spatial patterns of moist static instability. This study found that rainbands in the inner core and distant rainband regions responded differently to changes in land surface moisture. Within the inner core region of the TC, WETX produced more precipitation that was more symmetrical compared with DRYX. In DRYX, there was increased moist static instability in the outer rainband region over water and decreased moist static instability in the outer rainband region over land, which may have contributed to the enhanced precipitation asymmetries. Still, both experiments produced asymmetrical precipitation distributions, suggesting that alterations to land surface moisture had a minor impact on the precipitation asymmetries in Hurricane Florence. We conclude that precipitation asymmetries are primarily dynamically driven by weak to moderate vertical wind shear and asymmetries in moisture flux convergence.

Quantifying the Impacts of High‐Resolution Urban Information on the Urban Thermal Environment

AbstractDetailed urban information, including land use/land cover (LULC), anthropogenic heat (AH) release, and urban canopy parameters (UCP), play critical roles in meteorological field simulations. It is particularly relevant for the Weather Research and Forecasting (WRF) model coupled with the single‐layer urban canopy model (SLUCM). Thus, we develop high‐resolution LULC, AH, and UCP data sets for Nanjing, a megacity in China, and conduct a series of numerical experiments with WRF/SLUCM to evaluate the impacts of urban parameters on the urban thermal environment. Model simulations with LULC scenarios have good agreement with the observed 2‐m temperature with a correlation coefficient of around 0.85, and present strong spatial homogeneity due to the more realistic representation of urban categories. The LULC change directly decreases the surface wind speed and increases (decreases) the sensible (latent) heat flux ( ()) in urban areas during the daytime; meanwhile increases and releases ground heat storage () during the nighttime, resulting in urban warming by 0.91°C in urban areas, compared with the control simulation (CTL) that does not take into account urban surfaces. In the LULC experiments combined with the UCP or AH, the UCP change enhances and releases more during nighttime, which increases by 0.13°C relative to LULC simulation. Also, the UCP effect reduces surface roughness and increases the width of the urban canopy, resulting in slightly enhanced wind speed, which is favorable for a warming environment in the urban area; the AH change contributes to increasing by 0.19°C through directly enhancing relative to LULC simulation. AH combined with the UCP further strengthens the UCP effect in the urban area. Overall, the influence of urban parameters on the is more pronounced during nighttime than daytime, which presents a decreasing trend with an increase in wind speed and spatial humidity in the urban area.

The Impacts of Midlevel Moisture on the Structure, Evolution, and Precipitation of Afternoon Thunderstorms: A Real-Case Modeling Study at Taipei on 14 June 2015

Abstract A severe afternoon thunderstorm (ATS) system developed within the Taipei basin on 14 June 2015, which produced intense rainfall (with a rainfall rate of 131 mm h−1) and urban-scale flooding. A control simulation (CNTL) using the Weather Research and Forecasting (WRF) Model with the horizontal grid size nested down to 500 m was performed to capture reasonably well the onset of the sea breeze, the merger of convective cells, and the evolution of the afternoon thunderstorm system. Four numerical sensitivity experiments with the increase or decrease of midlevel (700–500 hPa) relative humidity (RH) of 10% and 20% were conducted, and simulation results were compared with those from the CNTL. Although the response of convection to midlevel RH was somewhat nonlinear, sensitivity experiments showed that a dry layer at middle levels would result in stronger cold pool, more intense convection, stronger updraft, more graupel particles, stronger net latent heating above the melting level, and a much larger area of the potential flooding region [>40 mm (30 min)−1]. The estimation of bulk entrainment rate provided evidence that the entrainment rate could be reduced by stronger cold pool and the widening of moist convection area. Three terrain-removal sensitivity experiments indicated that Taipei basin modulated the response of convection intensity to midlevel RH. The basin terrain confined the outflow associated with ATS and forced it to converge with the moist sea breeze continuously, providing a favorable dynamic and thermodynamic environment for subsequent convection development. This “basin confinement effect” may be crucial for short-duration rainfall extremes over complex terrain. Significance Statement This study has examined the impact of midlevel moisture on the structure, evolution, and precipitation of an afternoon thunderstorm system that produced intense rainfall at Taipei using eight numerical experiments based on high-resolution model outputs. Our findings explain how a drier layer at middle levels would produce a more intense thunderstorm system, although the response of convection intensity to midlevel moisture is somewhat nonlinear. In addition, it is found that terrain could modulate the response of convection to midlevel moisture, which is rarely discussed in previous studies.

The Impact of Intra-Seasonal Oscillation on Westward Track Deflection of Super Typhoon Fitow (2013)

Typhoon Fitow (2013) took an unusual westward track deflection after a lengthy northward movement over the western North Pacific (WNP). Based on observation and wave analysis, it is found that the track deflection of Fitow is attributed to the transition of environmental flow from meridional to zonal orientation, which is closely associated with a low-frequency intra-seasonal oscillation (ISO). Furthermore, the impact of ISO on tropical cyclone (TC) unusual movement is investigated using the Advanced Research version of Weather Research and Forecasting (WRF-ARW) model. The control simulation (CTL) reproduces well the synoptic pattern and track deflection of the TC. The TC moves straightly westward and northwestward without track deflection in the sensitivity experiments with the removal of total ISOs and the west-propagating ISO component, while keeping the recurving track with the removal of east-propagating ISO, which suggests that the west-propagating ISO plays a dominant role in the westward track deflection. In the experiment of removing west-propagating ISOs, an anomalous southeast–northwest-oriented wave train around the TC is modified, the mid-latitude trough decays, and the enhanced zonally elongated subtropical high is responsible for the straight northwestward motion of the TC. However, after removing a weaker convection anomaly associated with east-propagating ISOs in the form of a southwest–northeast oriented dipole circulation, the TC is affected by a sustained shallow mid-latitude trough and a west-extended ridge of subtropical high to keep the cyclonic track turning analogous to the counterpart in CTL. The piecewise potential vorticity inversion diagnosis further assesses the contribution of the different ISO components to TC track deflection.

Sea surface temperature effects on the modelled track and intensity of tropical cyclone Gonu

ABSTRACT The seven simulations were performed to investigate the role of the sea surface temperature (SST) in numerical prediction of tropical cyclones (TCs). The TC Gonu, formed over the Arabian Sea in 2007, was selected for this study. The first five simulations were performed using WRF model. In the first simulation as control simulation (CTL), the SST derived from NCEP-MMAB was used. In the second simulation, 1°C was added to input SST, and in the third simulation, 1°C was subtracted to input SST. It was found that the deviation between the simulated track of simulation SST +1 and CTL is more significant than that between simulation SST −1 and CTL. For the fourth simulation, a homogeneous SST field over the entire basin was used. For the fifth simulation, SST anomaly was calculated, and its values were added to the entire domain. Removing the temperature gradient caused TC intensity to decrease and deviation of the track to the northeast; the increasing temperature gradient had a lower impact on the TC intensity but with a significant deviation of the track to the north with respect to the CTL simulation. In the sixth simulation to consider cyclone-induced SST cooling, a one-dimensional oceanic mixed layer scheme was applied. Results showed no significant reduction in TC intensity. In the seventh simulation, the COAWST modelling system was used. The simulated SST of the COAWST model was consistent with the satellite observations, which finally led to improve the simulation of track and intensity of TC Gonu.

Exploring Inland Tropical Cyclone Rainfall and Tornadoes under Future Climate Conditions through a Case Study of Hurricane Ivan

AbstractThe overarching purpose of this study is to investigate the impacts of anthropogenic climate change both on the rainfall and tornadoes associated with tropical cyclones (TCs) making landfall in the U.S. Atlantic basin. The “pseudo–global warming” (PGW) approach is applied to Hurricane Ivan (2004), a historically prolific tropical cyclone tornado (TCT)-producing storm. Hurricane Ivan is simulated under its current climate forcings using the Weather Research and Forecasting Model. This control simulation (CTRL) is then compared with PGW simulations in which the current forcings are modified by climate-change differences obtained from the Community Climate System Model, version 4 (NCAR); Model for Interdisciplinary Research on Climate, version 5 (MIROC); and Geophysical Fluid Dynamics Laboratory Climate Model, version 3 (GFDL). Changes in TC intensity, TC rainfall, and TCT production, identified for the PGW-modified Ivan, are documented and analyzed. Relative to CTRL, all three PGW simulations show an increase in TC intensity and generate substantially more accumulated rainfall over the course of Ivan’s progression over land. However, only one of the TCs under PGW (MIROC) produced more TCTs than CTRL. Evidence is provided that, in addition to favorable environmental conditions, TCT production is related to the TC track length and to the strength of the interaction between the TC and an environmental midlevel trough. Enhanced TCT generation at landfall for MIROC and GFDL is attributed to increased values of convective available potential energy, low-level shear, and storm-relative environmental helicity.

Dynamical Downscaling of Future Hydrographic Changes over the Northwest Atlantic Ocean

AbstractProjected climate changes along the U.S. East and Gulf Coasts were examined using the eddy-resolving Regional Ocean Modeling System (ROMS). First, a control (CTRL) ROMS simulation was performed using boundary conditions derived from observations. Then climate change signals, obtained as mean seasonal cycle differences between the recent past (1976–2005) and future (2070–99) periods in a coupled global climate model under the RCP8.5 greenhouse gas trajectory, were added to the initial and boundary conditions of the CTRL in a second (RCP85) ROMS simulation. The differences between the RCP85 and CTRL simulations were used to investigate the regional effects of climate change. Relative to the coarse-resolution coupled climate model, the downscaled projection shows that SST changes become more pronounced near the U.S. East Coast, and the Gulf Stream is further reduced in speed and shifted southward. Moreover, the downscaled projection shows enhanced warming of ocean bottom temperatures along the U.S. East and Gulf Coasts, particularly in the Gulf of Maine and the Gulf of Saint Lawrence. The enhanced warming was related to an improved representation of the ocean circulation, including topographically trapped coastal ocean currents and slope water intrusion through the Northeast Channel into the Gulf of Maine. In response to increased radiative forcing, much warmer than present-day Labrador Subarctic Slope Waters entered the Gulf of Maine through the Northeast Channel, warming the deeper portions of the gulf by more than 4°C.

Response of surface air temperature to the change of leaf area index in the source region of the Yellow River by the WRF model

Leaf area index (LAI) is a crucial land-atmosphere exchange parameter. LAI change can cause a variation of other land surface parameter. In this research, three experiments were conducted to investigate the impact of LAI and albedo change on surface air temperature in the source region of the Yellow River (SRYR) using the Weather Research and Forecasting (WRF) model. Three experiments used the same settings, initial and boundary conditions except for the LAI and albedo data. The control simulation (CTL) used the WRF model climatological LAI data, the second simulation (LAI) used the Moderate Resolution Imaging Spectroradiometer (MODIS) LAI data, and the third simulation (LAIALB) used the MODIS LAI and MODIS albedo. The results show MODIS LAI is greater by 34.5% than WRF climatological LAI, and the MODIS albedo is lower by 24.3% than WRF climatological albedo over the whole growing season of 2006 in SRYR. All the experiments can simulate the surface air temperature (Ta) spatial distribution characteristics, but underestimate the values of 1.3 °C in CTL experiment and 0.6 °C in LAIALB experiment in SRYR. The simulated Ta by LAI experiment is lower 0.1 °C than by the CTL experiment, but the simulated Ta by the LAIALB experiment is obviously higher 0.6 °C than the CTL experiment. The LAI experiment shows a cooling effect because the higher MODIS LAI decreases the canopy resistance, which induces a positive average 2.1 Wm−2 latent heat flux (LH) and a negative average − 2.1 Wm−2 sensible heat flux (Hs). The LAIALB experiment presents a warming effect because of low MODIS albedo comparing WRF albedo, which changes the radiation components and results in an obvious negative − 14.0 Wm−2 upward short wave radiation, a positive 11.7 Wm−2 net radiation, and a positive 10.9 Wm−2 heat flux. In fact, more precipitation produces more snow and high surface albedo in the WRF model, which results in a cold temperature bias in SRYR.

Regional Data Assimilation with the NCMRWF Unified Model (NCUM): Impact of Doppler Weather Radar Radial Wind

The Indian sub-continent often receives heavy rainfall events, especially during active phases of the south-west monsoon (SWM). The accurate prediction of such events requires a high-resolution model with data assimilation techniques which can assimilate high-density spatial and temporal observed data, like radar observations. This study is undertaken to evaluate the impact of assimilation of radial velocity from multiple Doppler weather radars (DWRs) for simulation of three convective rainfall events during the SWM using the high-resolution (4 km) National Centre for Medium Range Weather and Forecasting (NCMRWF) Unified Model (NCUM) with a three-dimensional variational (3DVAR) data assimilation system. Two numerical experiments are carried out viz. control simulation (CNTL) and a second experiment (RAD, assimilation of all observations used in CNTL plus radial winds from Indian DWRs). The study clearly shows that the assimilation of DWR data has a positive impact in the simulation of heavy rainfall events by the model. The root mean square error (RMSE) of the analyzed (simulated) u- and v-components of wind is reduced by 46% (25%) and 37% (19%) in the RAD experiment as compared to the CNTL experiment. The simulated wind fields at different pressure levels are stronger after assimilation of DWR observations, and it is also successfully produced the cyclonic circulation as compared to the CNTL simulation. The skew-T plots suggested that the convection is more properly represented by the RAD experiment than the CNTL. The value of stability parameters is properly simulated in the RAD experiment, while compared with the CNTL, the values are reasonably well matched with the observed values in all cases. The intensity of the rainfall is reasonably well simulated by the RAD as compared to the CNTL experiment. The statistical skill scores of rainfall with different thresholds are significantly improved in the RAD experiment for all the cases.

Impact of Vortex Initialization in Prediction of Tropical Cyclones over Bay of Bengal with NCUM Model

The present study evaluates the impact of vortex initialization (VI) scheme within the NCMRWF Global Unified model (NCUM-G) for prediction of tropical cyclones (TCs) formed over Bay of Bengal (BoB). For this purpose, two numerical experiments such as control simulation (CNTL) without using VI scheme and VOTX simulation using the VI scheme in the NCUM-G are performed by considering four landfalling TCs formed over BoB basin during the year 2016–17. The results suggest that even though TCs are large synoptic systems, the introduction of VI scheme has a positive impact on the prediction of the location, movement, intensity and development of rain bands associated with the TCs. The initial vortex position and landfall position errors are reduced by ∼64% and ∼39% in VOTX simulations over CNTL, respectively. The mean track errors of all the four TCs are reasonably improved by ∼58% in VOTX over CNTL. The equitable threat score (ETS) and frequency bias are significantly improved in the VOTX for all the TC cases as compared to CNTL. Study results provide a positive proof of concept that the VI scheme within the NCUM-G can help to improve the simulation of track and intensity of TCs over BoB.

Impact of upstream moisture structure on a back-building convective precipitation system in south-eastern France during HyMeX IOP13

Abstract. The present study examines the impact of the environmental moisture structure in the lower troposphere (below 2 km above sea level, a.s.l.) on the precipitation development, observed in southern France during Intensive Observation Period (IOP) 13 of the first Special Observation Period of the Hydrological cycle in the Mediterranean Experiment (HyMeX SOP-1), through a series of sensitivity experiments using the non-hydrostatic mesoscale atmospheric numerical model (Meso-NH). The control simulation (CNTL) and all the other 12 sensitivity experiments examined in this study succeed in reproducing a heavy precipitation event (HPE) in the coastal mountainous region of Var in south-eastern France as observed. The sensitivity experiments are designed to investigate the response of the HPE to the variability of the water vapour content upstream in the moist marine atmospheric boundary layer (MABL) and the drier air above. The comparisons between CNTL and the 12 sensitivity experiments show how the life cycle of precipitation associated with the HPE, but also the upstream flow (over the sea), is modified, even for moisture content changes of only 1 g kg−1 below 2 km a.s.l. Within the low-level wind convergence between southerlies and south-westerlies, a small increase of moisture content in the MABL prolongs moderate precipitation (≥5 mm in 15 min) and enlarges the area of weak precipitation (≥1 mm in 15 min). The moistening in the 1–2 km a.s.l. layer, just above the MABL, prolongs the duration of moderate precipitation, for a similar total precipitation amount as in CNTL. The drier MABL and 1–2 km a.s.l. layer shorten the lifetime of precipitation and reduce the total precipitation amount with respect to CNTL. We also found that the moisture in the MABL has a stronger impact on producing enhanced precipitation (both in terms of amount and intensity) than the moisture just above (1–2 km a.s.l.). Also, it is worth noting that adding moisture in the MABL does not necessarily lead to enhanced precipitation amount. In moistening the MABL, the duration of moderate precipitation increases with increasing moisture as does the area covered by weak precipitation, while the area covered by the intense precipitation (≥30 mm) decreases. Despite a simplified moisture-profile modification approach, this study suggests that moisture structure in the lower troposphere is key for accurate prediction at short-term range of the timing and location of precipitation in the coastal mountainous region in southern France.

Potential impact of sea surface temperature on rainfall over the western Philippines

ᅟThe study used a 5 km-resolution regional climate model, the Advanced Research Weather Research and Forecasting Model, to quantify the potential impact of sea surface temperature (SST) west of the Philippines on summer monsoon rainfall on the northwestern coast of the country. A set of control simulations (CTL) driven by ERA-Interim reanalysis data and the monthly National Oceanic and Atmospheric Administration Optimum Interpolation SST dataset was performed for the months of June to August of 1982–2012. A second set of simulations driven by climatological SST values was performed for the same period. The difference between these two simulation sets is analyzed to determine the sensitivity of rainfall to interannual variations in local SST, not remote SST, via a regional climate model. The CTL simulations represented spatial and temporal variations in rainfall well, yielding realistic climatological rainfall values with high spatial correlations with observations. The interannual correlation of monthly rainfall over the northwestern region of the Philippines was also high when compared to observations. The results showed that positive SST anomalies west of the Philippines induced positive rainfall anomalies in the northwestern Philippines via an increase in latent heat flux from the sea surface, implying that summer monsoon rainfall in the northwestern Philippines is modulated by interannual variations in SST west of the Philippines. The impact of SST on latent heat flux and rainfall were 20–40%, greatly exceeding the 7% approximation from the Clausius–Clapeyron equation, which can be explained by the enhancement of low-level winds and a weak warming of surface air temperature over the ocean.

Attribution of the Observed Spring Snowpack Decline in British Columbia to Anthropogenic Climate Change

Abstract A detection and attribution analysis on the multidecadal trend in snow water equivalent (SWE) has been conducted in four river basins located in British Columbia (BC). Monthly output from a suite of 10 general circulation models (GCMs) that participated in phase 5 of the Coupled Model Intercomparison Project (CMIP5) is used, including 40 climate simulations with anthropogenic and natural forcing combined (ALL), 40 simulations with natural forcing alone (NAT), and approximately 4200 yr of preindustrial control simulations (CTL). This output was downscaled to ° spatial resolution and daily temporal resolution to drive the Variable Infiltration Capacity hydrologic model (VIC). Observed (manual snow survey) and VIC-reconstructed SWE, which exhibit declines across BC, are projected onto the multimodel ensemble means of the VIC-simulated SWE based on the responses to different forcings using an optimal fingerprinting approach. Results of the detection and attribution analysis shows that these declines are attributable to the anthropogenic forcing, which is dominated by the effect of increases in greenhouse gas concentration, and that they are not caused by natural forcing due to volcanic activity and solar variability combined. Anthropogenic influence is detected in three of the four basins (Fraser, Columbia, and Campbell Rivers) based on the VIC-reconstructed SWE, and in all basins based on the manual snow survey records. The simulations underestimate the observed snowpack trends in the Columbia River basin, which has the highest mean elevation. Attribution is supported by the detection of human influence on the cold-season temperatures that drive the snowpack reductions. These results are robust to the use of different observed datasets and to the treatment of low-frequency variability effects.

A climatological validation of urban air temperature and electricity demand simulated by a regional climate model coupled with an urban canopy model and a building energy model in an Asian megacity

ABSTRACTIn this study, we validated urban air temperature and electricity demand by a year‐round numerical simulation using a regional climate model coupled with an urban canopy model and a building energy model (RCM‐UCM+BEM) in the Asian megacity, Osaka, which is the largest metropolis in Japan after Tokyo. The control simulation (CTRL), which was based on the use of central air‐conditioning (AC) systems, reproduced the surface air temperatures observed in Osaka City in the summer cooling and interim seasons, but underestimated midnight to morning temperatures by over 2 °C in the winter heating season. In addition, the CTRL significantly overestimated the electricity demand in Osaka City in both the cooling and heating seasons, when the AC load was increased. These errors were likely due to the overestimation of AC use in the CTRL model because, in Japan, central AC systems are not used in business and residential areas, where individual AC units are mainly used. To prevent this overestimation, we introduced three new parameters to consider the use of partial AC systems in the model. The results of the new numerical experiment remarkably reduced the underestimation of temperature and the overestimation of electricity demand. This suggests that the RCM‐UCM+BEM modified by this study is effective for not only reproducing the current status of seasonal urban air temperature and electricity demand in Osaka, but also for projecting the future situation in other mega cities.

The Realization of Extreme Tornadic Storm Events under Future Anthropogenic Climate Change

Abstract This research seeks to answer the basic question of how current-day extreme tornadic storm events might be realized under future anthropogenic climate change. The pseudo global warming (PGW) methodology was adapted for this purpose. Three contributions to the CMIP5 archive were used to obtain the mean 3D atmospheric state simulated during May 1990–99 and May 2090–99. The climate change differences (or Δs) in temperature, relative humidity, pressure, and winds were added to NWP analyses of three high-end tornadic storm events, and this modified atmospheric state was then used for initial and boundary conditions for real-data WRF Model simulations of the events at high resolution. Comparison of an ensemble of these simulations with control simulations (CTRL) facilitated assessment of PGW effects. In contrast to the robust development of supercellular convection in each CTRL, the combined effects of increased convective inhibition (CIN) and decreased parcel lifting under PGW led to a failure of convection initiation in many of the experiments. Those experiments that had sufficient matching between the CIN and lifting tended to generate stronger convective updrafts than CTRL, although not in proportion to the projected higher levels of convective available potential energy (CAPE) under PGW. In addition, the experiments with enhanced updrafts also tended to have enhanced vertical rotation. In fact, such supercellular convection was even found in simulations that were driven with PGW-reduced environmental wind shear. Notably, the PGW modifications did not induce a change in the convective morphology in any of the PGW experiments with significant convective storminess.

On the Rapid Intensification of Hurricane Wilma (2005). Part III: Effects of Latent Heat of Fusion

Abstract The impacts of the latent heat of fusion on the rapid intensification (RI) of Hurricane Wilma (2005) are examined by comparing a 72-h control simulation (CTL) of the storm to a sensitivity simulation in which the latent heat of deposition is reduced by removing fusion heating (NFUS). Results show that, while both storms undergo RI, the intensification rate is substantially reduced in NFUS. At peak intensity, NFUS is weaker than CTL by 30 hPa in minimum central pressure and by 12 m s−1 in maximum surface winds. The reduced rate of surface pressure falls in NFUS appears to result hydrostatically from less upper-level warming in the eye. It is shown that CTL generates more inner-core convective bursts (CBs) during RI, with higher altitudes of peak vertical motion in the eyewall, compared to NFUS. The latent heat of fusion contributes positively to sufficient eyewall conditional instability to support CB updrafts. Slantwise soundings taken in CB updraft cores reveal moist adiabatic lapse rates until 200 hPa, where the updraft intensity peaks. These results suggest that CBs may impact hurricane intensification by inducing compensating subsidence of the lower-stratospheric air, and the authors conclude that the development of more CBs inside the upper-level radius of maximum wind and at the higher altitude of latent heating all appear to be favorable for the RI of Wilma.

An Oceanic Impact of the Kuroshio on Surface Air Temperature on the Pacific Coast of Japan in Summer: Regional H2O Greenhouse Gas Effect

Abstract This study used a 4-km resolution regional climate model to examine the sensitivity of surface air temperature on the Pacific coast of Japan to sea surface temperature (SST) south of the Pacific coast of Japan during summer. The authors performed a control simulation (CTL) driven by reanalysis and observational SST datasets. A series of sensitivity experiments using climatological values from the CTL SST datasets over a 31-yr period was conducted. The interannual variation in surface air temperature over the Pacific coast was well simulated in CTL. The interannual variation in SST over the Kuroshio region amplified the interannual variation in surface air temperature over the Pacific coast. It was found that 30% of the total variance of interannual variation in surface air temperature can be controlled by interannual variation in SST. The calculated surface air temperature on the Pacific coast increased by 0.4 K per 1-K SST warming in the Kuroshio region. Note that this sensitivity was considerably greater during nighttime than during daytime. Concurrent with the warming in surface air temperature, downward longwave radiation at the surface was also increased. In summer, the increase in latent heat flux was considerably larger than that in sensible heat flux over the ocean because of SST warming, according to the temperature dependence of the Bowen ratio. This implies that the primary factor for the increase in surface air temperature in summer is increased moisture in the lower troposphere, indicating that the regional warming was caused by an increase in H2O greenhouse gas.

Modelling of mineral dust for interglacial and glacial climate conditions with a focus on Antarctica

Abstract. The mineral dust cycle responds to climate variations and plays an important role in the climate system by affecting the radiative balance of the atmosphere and modifying biogeochemistry. Polar ice cores provide unique information about deposition of aeolian dust particles transported over long distances. These cores are a palaeoclimate proxy archive of climate variability thousands of years ago. The current study is a first attempt to simulate past interglacial dust cycles with a global aerosol–climate model ECHAM5-HAM. The results are used to explain the dust deposition changes in Antarctica in terms of quantitative contribution of different processes, such as emission, atmospheric transport and precipitation, which will help to interpret palaeodata from Antarctic ice cores. The investigated periods include four interglacial time slices: the pre-industrial control (CTRL), mid-Holocene (6000 yr BP; hereafter referred to as "6 kyr"), last glacial inception (115 000 yr BP; hereafter "115 kyr") and Eemian (126 000 yr BP; hereafter "126 kyr"). One glacial time interval, the Last Glacial Maximum (LGM) (21 000 yr BP; hereafter "21 kyr"), was simulated as well to be a reference test for the model. Results suggest an increase in mineral dust deposition globally, and in Antarctica, in the past interglacial periods relative to the pre-industrial CTRL simulation. Approximately two-thirds of the increase in the mid-Holocene and Eemian is attributed to enhanced Southern Hemisphere dust emissions. Slightly strengthened transport efficiency causes the remaining one-third of the increase in dust deposition. The moderate change in dust deposition in Antarctica in the last glacial inception period is caused by the slightly stronger poleward atmospheric transport efficiency compared to the pre-industrial. Maximum dust deposition in Antarctica was simulated for the glacial period. LGM dust deposition in Antarctica is substantially increased due to 2.6 times higher Southern Hemisphere dust emissions, 2 times stronger atmospheric transport towards Antarctica, and 30% weaker precipitation over the Southern Ocean. The model is able to reproduce the order of magnitude of dust deposition globally and in Antarctica for the pre-industrial and LGM climates.