A43B-1137
Future Climate Projection over East Asia Using ECHO-G/S
Future climate projection based on IPCC SRES (20C3M and A1B, B1 and A2 scenarios) is completed using ECHO-G (ECHAM4/HOPE-G) with GHG and aerosol. In each scenario, two member ensemble runs are carried out. Simulations produced reliable present climate state, even though there are cold bias in temperature and dry bias in summertime precipitation. At the end of 21st century, global mean surface temperature projects to rise 1.8¡É, 2.6¡É, 3.0¡É under B1, A1B, A2 scenarios with respect to the period of 1980-1999. This suggests that higher GHG concentration has larger response in global warming. The ensemble-averaged spatial responses of JJA and DJF mean patterns are very similar through all the experiments. The ensemble range is smaller than the different among scenarios, except for changes of local precipitation. The greatest warming occurs at high northern latitudes and over lands with increase of precipitation. East Asian region may experience warmer and wetter climate and the amplitudes are larger than those in global mean. In particular, the temperature rising in winter and increase in the summer precipitation are clearly outstanding. In spite of large uncertainty of simulated precipitation in regional scale, the precipitation has highly variability and the summer precipitation amount has significantly increased (decreased) over the eastern coast (inland) of East Asia. The results point out that East Asia may suffer from extreme events such as drought and flood. Therefore this study analyzes changes in intensity and frequency of climate extremes as well as in the climate state for seasonal temperature and precipitation. In order to estimate the frequency of extreme events in global warming over East Asia, we have examined daily maximum and minimum temperatures and daily precipitation amounts for the period of 2080-2099 relative to the period of 1980-19999. According to the results, increase of minimum temperature is larger than that of maximum temperature by about 0.5¡É. The number of days with minimum temperature below 0¡É has decreased in winter and that of maximum temperature above 30¡É has increased in summer. The number of days with daily precipitation exceeding 50 mm/day has remarkably increased over coastal region while the frequency of non-precipitation has increased over East Asian inland. The results indicate that the opposed extreme events are likely to occur over the inland and eastern coast of East Asia by global warming.
A43B-1138
The Rainfall Phenomena during the Pre-Monsoon Period over the Northeastern Part of Indian Subcontinent in 2007
The rainfall phenomena during the pre-monsoon period over the northeastern part of Indian subcontinent in 2007 are investigated using OLR and the NCEP/NCAR reanalysis data during the period from March to May in 2007. Moreover, for the purpose of clarifying the atmospheric condition and the structure of the disturbance during the pre-monsoon period, we carried out the upper air observation at Dhaka in Bangladesh during the period from 20 April to 15 May in 2007. The time series of OLR over Bangladesh (22.5--27.5 ° N, 87.5--92.5 ° E) from March to May in 2007 is calculated. It is well known that an average monsoon onset over Bangladesh occurs in early June [e.g., Ahmed and Karmakar, 1993; Wang and LinHo, 2002]. In March, the convection activity becomes suppressed. During the IOP, we can divide it into 3 stages (A: 20--27 April, B: 28 April -- 5 May, C: 6--14 May) by the OLR value indicated the convective activity. During stages A and C, there is comparatively convection activity. On the other hand, and the convection activity become suppressed during stage B. Actually, the mesoscale disturbance activity with a dead person is active in A. Although the convective activity during spell C is active, there was little rainfall by the ground observation. We carried out that the composite analysis of OLR about each period in stage A, B, and C. It is shown that the lower OLR region goes southward from the middle latitude in stage A. In addition, the lower OLR region of the southern part of the Indochina Peninsula goes northwestward from stage A to C. It is suggested that the eastward moving and passage of the trough of the upper air along the south slope of the Tibetan plateau brought the rainfall phenomena during the pre-monsoon period. The northeastern part of Indian subcontinent during the pre-monsoon period is affected by the middle latitude.
A43B-1139
Macroscale Circulation Patterns as Reflected in Spatial and Temporal Patterns of Precipitation over the Tibetan Plateau
Circulation patterns such as the NAO, PNA, and AO have been known to impact climate both near the action centers and at great distances away. These macroscale circulation patterns can impact regional wind patterns, temperature gradients and pressure gradients. Changes in these gradients can cause an onset of various weather conditions including precipitation. Precipitation across the Tibetan Plateau is influenced by known phenomena such as monsoon systems and teleconnections. Previous studies have suggested that other forcing mechanisms also may play a vital role in influencing precipitation in this region. To evaluate potential forcing factors affecting precipitation across the Tibetan Plateau, the relationship between the spatial and temporal patterns of precipitation and the regional and macroscale circulation patterns will be investigated. To explore this relationship statistical analysis, such as Principal Component Analysis (PCA), Correlation Field Analysis, and Canonical Correspondence Analysis (CCA), is preformed. This study also incorporates tree ring chronologies from Qilian junipers (Sabina przewalskii Kom.) sampled in the Qaidam Basin, northeastern Tibetan Plateau. These data have been used in previous studies to indicate environmental change, and tree rings taken from this region have shown signatures of circulation patterns such as Arctic Oscillation (AO). Based on the relationship between tree ring data and circulation patterns it is possible to reconstruct past events. This information along with examination of National Centers for Environmental Protection/National Center for Atmospheric Research (NCEP/NCAR) Reanalysis data will aid in the examination of the relationship between teleconnection patterns and precipitation, and develop a greater understanding of the precipitation variability across the Tibetan Plateau.
A43B-1140
Spatio-temporal Variability of Precipitation over northern Africa
The statistical properties of precipitation events from various satellite products are investigated for northern Africa during the rainy summer season. Different statistical measures, including correlation function and critical success indices, are employed. The spatial scales of interest range from 4 km to 100 km, and the temporal scales of interest range from instantaneous to monthly. The statistics are conditioned on different rainfall rates. The statistics clearly indicate the considerable geographical variability of precipitation variability. The results of this study will be useful for downscaling coarse precipitation fields, and for evaluating satellite-derived precipitation estimates.
A43B-1141
Radar Observations of West African Monsoon Precipitation: Evolution of the 2006 Monsoon Season
The African Monsoon Multidisciplinary Activities (AMMA) Intensive Observational Period, which took place during the summer of 2006, provided a wealth of information regarding the onset and development of the monsoon season over the Sahel region of West Africa. Radar observations near Niamey, Niger during AMMA documented the structure, motion, and precipitation of convective cloud systems during the monsoon season. A radar-based analysis of convective storm development and propagation, with particular focus on mesoscale convective systems (MCSs), was performed. Radar reflectivity data collected by the MIT scanning C-band radar during the months of July – September were processed and quality-controlled to remove non-meteorological echo. An objective algorithm separated radar echo into convective cell and stratiform components. Time series of rainfall produced from radar reflectivity values, partitioned by mesoscale vs. isolated convective cell organization, were analyzed. August was the most active month for precipitation, while the beginning of July and end of September corresponded to the onset and decline, respectively of the monsoon season in Niamey. As expected, MCS-scale systems produced the greatest amount of rainfall, with a near equal precipitation distribution from the convective and stratiform portions. Spectral analysis revealed significant diurnal variation of rainfall, with a late afternoon maximum, later than in other tropical land locations. The radar rainfall time series compares well with the GPCP satellite 1 deg. x 1 deg. rain product. Time variation of the vigor of convection, as measured by the 30 dBZ surface height in convective cells, revealed the strongest convection generally occurred in August, associated with organized squall line systems. A parallel analysis of MCS and isolated convection occurrence with respect to timing of the African Easterly Jet (AEJ) will be presented, to examine whether organized convective systems occurred preferentially within easterly wave troughs.
A43B-1142
Pacific Sea Surface Temperatures in the Twentieth Century: An Evolution-Centric Analysis of Variability and Trend
A consistent analysis of natural variability and secular trend in Pacific SSTs in the 20th century is presented. By focusing on spatial and temporal recurrence, but without imposition of periodicity constraints, this single analysis discriminates between biennial, ENSO and decadal variabilities, leading to refined evolutionary descriptions; and between these natural variability modes and secular trend; all without advance filtering (and potential aliasing) of the SST record. SST anomalies of all four seasons are analyzed together using the extended-EOF technique. Canonical ENSO variability is encapsulated in two modes that depict the growth (east-to-west along the equator) and decay (near-simultaneous amplitude loss across the basin) phases. Another interannual mode, energetic in recent decades, is shown linked to the west-to-east SST development seen in post climate-shift ENSOs; the non- canonical ESNO mode. The mode is closely related to Chiang and Vimont's meridional mode, and leads to some reduction in canonical ENSO's oscillatory tendency. Pacific decadal variability is characterized by two modes: The Pan-Pacific mode has a horse-shoe structure with the closed end skirting the North American coast; and a quiescent eastern equatorial Pacific. The mode exhibits surprising connections to the tropical/subtropical Atlantic, with correlations there resembling the Atlantic Multidecadal Oscillation. The second decadal mode---the North Pacific mode---captures the 1976/77 climate shift and is closer to Mantua's Pacific Decadal Oscillation. Our analysis shows, perhaps, for the first time, the striking links of the North Pacific mode to the western tropical Pacific and Indian Ocean SSTs. The physicality of both modes is assessed from correlations with the Pacific biological time series. Finally, the secular trend is characterized: Implicit accommodation of natural variability leads to a non-stationary SST trend, including mid-century cooling. The SST trend is remarkably similar to the global surface air temperature trend. Geographically, a sliver of cooling in found in the central equatorial Pacific in the midst of wide- spread but non-uniform warming in all basins. An extensive suite of sensitivity tests, including counts of the number of observational analogs of the modes in test analyses, support the robustness of this analysis.
A43B-1143
Statistical analysis of the interannual and decadal climate variability in Western Pacific
The interannual and decadal climate variability in Western Pacific is statistically analyzed using satellite data, ECMWF reanalysis and two IPCC AR4 model results. Regional warming is detected by the long term climate variables trends, such as Sea Surface Temperature (SST) and total column Atmospheric Water Vapor (AWV). Both modeled time series for the last century show an increasing trend as expected, suggesting the possibility of global warming, while some discrepancies are observed among the models and observation. The decadal trends of SST and AWV in most areas are increasing accordantly in models and reanalysis data except Southern Hemisphere, and the increasing in 1990s. The scaling coefficients in Western Pacific in both models show increasing and positive trends. However, the satellite data show a negative coefficient during 1998-2006. Further correlation analysis for these climate variables (SST¡BAWV and Wind Speed) is used to investigate the local characteristics in Western Pacific, where inconsistency exists. The correlation distribution suggests that the AWV not only relates to SST but also are affected by other dynamic processes such as monsoon and El Niño. Significant difference is observed between the models from 30¢XN to 40¢XN in both summer and winter. Empirical Orthogonal Functions (EOF) is then used to analyze the spatial patterns of climate change in Western Pacific. These EOF patterns show that the climate variables are mostly dominant by the interannual and decadal climate variability and dynamics of Pacific.
A43B-1144
Climatological characteristics of tropical cyclones making landfall over the Korean Peninsula
We investigated the climatological characteristics of Korean peninsula (KP) landfall tropical cyclones (TCs) during the period 1951-2004. Landfall frequency has increased since the late 1980s. Especially, that of TCs with a greater intensity than tropical storm (TS) has rapidly increased. The pattern of landfall changed from the middle or northern region of the west coast of the KP to the south coast of the KP. That is, the tracks of the landfalling TCs tend to shift southeastward in recent years. The recurving location has also tended to shift southeastward in recent years. Through analysis of the variations of the accumulate cyclone energy (ACE), central pressure at and after recurving, convective activity, and SST in the western North Pacific (WNP), the intensity of landfall TCs has been rapidly increasing on average since the late 1980s. These results are consistent with the fact that TCs causing the most serious economic damage in South Korea happened after the late 1980s. This is because the TCs that make landfall over the KP more often take the track to pass over the sea (e.g., East China Sea), which enables the TC to take more energy from the sea. The western North Pacific High (WNPH) has tended to shift eastward in recent years. This eastward shift of the WNPH is related to the southward advance of the upper-level trough at the mid-latitude and the eastward extension of subtropical monsoon westerlies. Therefore, all these changes related to KP-landfall TCs would be due to the eastward shift of the WNPH in recent years. The ENSO is known to considerably affect TC activity from various previous studies. The their common conclusion is that the main formation region of the TC moves southeastward, the TC recurves further eastward, and then the life span of the TC tends to be longer during the warm phase of ENSO. Meanwhile, in this study, the relationship between KP-landfall TC frequency and the ENSO was not investigated. This study focuses on the KP- landfall TCs and then the number of TCs to study is relatively not many. In a future study, a climatological analysis on TCs affected the KP will be made.
A43B-1145
Relationship between the ENSO and northward propagating intraseasonal oscillation associated with the East Asian summer monsoon
Observational studies are presented on the relationship between ENSO and the northward propagating intraseasonal oscillation (NPISO) in the East Asian Summer Monsoon (EASM) system. The summer NPISO activity shows a significant correlation with the preceding winter extreme phase of ENSO cycles. A higher correlation appears during late summer, consistent with frequent heavy rainfall events at that time as revealed in some previous case studies. The westwardly expanded broad anticyclonic circulation over the western North Pacific and the smaller cyclonic circulation around Korea and Japan are found to be associated with the NPISO activity. ENSO affects the late summer NPISO activity through an atmospheric bridge and downstream wave propagation; the springtime Indian Ocean sea surface temperature warming induced by ENSO through the Walker circulation leads to suppressed convection over the Philippine Sea and this generates the forced Rossby wave train, forming the above low-level circulation anomalies.
A43B-1146
Ozone Radiative Feedback on the Quasi-Biennial Oscillation in the Tropical Stratosphere as Revealed in Chemistry-Climate Model Simulations
Simulations on the recent past middle atmosphere were made with a chemistry-climate model (CCM) of Meteorological Research Institute (MRI). Three runs with different transport schemes for chemical species were performed for 25 years from 1980 to 2004. The three transport schemes are formally hybrid semi-Lagrangian type, which is of flux form in the vertical and, at once, of ordinary type in the horizontal, while they use different interpolation and/or approximation in calculating in-cell profiles from cell-average values, resulting in different properties in diffusiveness. The prototype scheme (Cubic3) uses a Lagrangian cubic interpolation of neighboring abundances in the horizontal and also uses it for overhead column abundances in the vertical. To the Cubic3 scheme, two improvements are successively incorporated: one is the piecewise rational-function method (PRM) in the vertical, and the other is a quintic Lagrangian interpolation in the horizontal, resulting in PRM3 (vertically PRM and horizontally cubic) and PRM5 (vertically PRM and horizontally quintic) schemes. The dynamics module of MRI-CCM is a spectral global model of T42 truncation with 68 layers extending from the surface to 0.01 hPa (about 80 km), wherein the vertical spacing is 500m in the stratosphere between 100 hPa and 10 hPa. Hines gravity wave (GW) drag is incorporated with an enhanced GW source in the tropics to spontaneously reproduce the QBO in zonal wind. The chemistry-transport module treats 36 long-lived species including 7 families, and 15 short-lived species with 80 gas phase reactions, 35 photochemical reactions and 9 heterogeneous reactions. MRI-CCM is integrated with observed forcings of SSTs, sea ice, volcanic aerosols, 11-year solar cycle, greenhouse gases, and halogens, the latter two of which are specified at the surface. It is found that PRM3 and PRM5 schemes substantially reduce the systematic positive bias in ozone, particularly in the tropical lower stratosphere and upper troposphere and that PRM5 reproduces most realistic ozone and other chemical species distributions with PRM3 being the next. For example, the ozone decrease amounts to about 40 % at 100hPa in PRM5 run. Along with these ozone reductions, the QBO period is also changed: it is about 27 months in Cubic3 run, while it is about 23 and 20 months for PRM3 and PRM5 runs. This shortening of the QBO period with the decrease in ozone abundance is compatible with authorsf previous simulations, in which switching on (off) of ozone radiative feedback prolongs (shortens) the QBO period by about 80 (35) %. In a less ozone condition in the lower stratosphere the ozone QBO amplitude also becomes smaller, so that the ozone radiative feedback weakens, resulting in a shorter QBO period.
A43B-1147
Low Frequency Variability and the Eastern Mediterranean Teleconnection Pattern
The long time series analysis of the atmospheric circulation has revealed large scale correlations between the flow at remote locations. These fluctuations belong in the low frequency range of timescale and referred to as teleconnections patterns. They are located in particular places and appear as preferred modes of low-frequency natural variability of the atmospheric circulation with fixed oscillating nodes and antinodes, called poles. These teleconnection patterns describe standing waves oscillating with time scales of a month or longer. It has been recognized that the large scale eddies and their feedback onto the mean flow, the propagation of Rossby waves in the midlatitudes and the stratosphere-troposphere interaction play an important role in understanding low frequency general circulation and variability. In previous studies, the Eastern Mediterranean Teleconnection pattern (EMP) was found with its two poles located in North-eastern Europe and Eastern Mediterranean, and it was predominantly identified at the upper troposphere during winter. An index was defined, based on the exact position of the two poles of the pattern, to represent the strength of the teleconnection pattern and to discriminate its positive and negative phase. The objective of this study is to investigate the large scale dynamics related to the development of EMP. For this purpose, datasets of daily geopotential height, temperature and horizontal wind components at several isobaric levels are employed, as obtained from the NCEP/NCAR and from the ECMWF centres, for the calculation of transient eddy kinetic energy, E-vectors, Rossby wave source and potential vorticity. It was found that the role of the eddy driven mid-latitude jet is important. It is likely that the subtropical jet is passive and that the transient eddies remove much more momentum in the negative phase, when the storm- track comes charging into Europe. Rossby wave propagation seems to determine the differing wave-guide aspects of the two EMP phases. In the negative phase, there is a significant southeastward Rossby wave propagation over Western Europe, while in the positive phase Rossby waves tend to move towards Scandinavia, consistent with the increased anticyclonic circulation over North Atlantic.
A43B-1148
Zonal Differences in the Interannual Variability of Baiu Front
The interannual variability of the Baiu frontal activity is examined in this work. In particular, the zonal differences are diagnosed from 1979 to 2002 (24 years), using NCEP/NCAR reanalysis and GPCP data in June. The interannual variability in Baiu precipitation shows significant zonal differences without temporal correlation. The western part is centered near the Tsushima current, while the eastern one appears on the Kuroshio current. We may zonally divide the Baiu phenomenon into two, i.e., the western Baiu (W-Baiu) and the eastern one (E- Baiu). Correlation analysis reveals that the interannual variability in the W-Baiu is associated with circulation in the tropical Pacific, while that in the E-Baiu seems to be related to the mid-latitude circulation over the Eurasian Continent. In fact, when the latter is dominant, the stationary Rossby wave activity is strong in the upper tropospheric westerly jet near 35N over the Eurasian Continent through Japan. The anomalous southward shift of the Asian jet, which is led by the enhancement of anticyclonic circulation in the southeastern part of the Tibetan High, contributes to the establishment of a waveguide for the Rossby wave propagation. At the eastern edge near Japan, the Rossby wave enhances the cyclonic circulation in the upper troposphere, which converges the water vapor for the anomalous precipitation in the E-Baiu. In contrast, the interannual variability in the W-Baiu is controlled by the anomalous meridional circulation in the western Pacific. The anomalous cyclones are located around East China and Southeast Asia, while the anomalous anticyclone is lain on the Philippine Sea between them. This anomalous pattern seems to be related to the so-called Pacific-Japan pattern in the western North Pacific. As such, the detailed inspection detects the differences in physical processes of the interannual Baiu activity.
A43B-1149
Recent Summer Sunshine Duration Variability and Trends Over the Iberian Peninsula: Relation With Changes in Circulation Patterns and Teleconnection With the Sahel Rainfall
This work describes the summer (July and August) time evolution and trends of sunshine duration (SunD) over the Iberian Peninsula (IP) covering the 1961-2004 period. We used the homogenized and gridded SUNDUIB database. The temporal evolution of the mean summer series for the whole IP shows a decrease in SunD from the 1960s to the early 1980s, followed by a slightly increase up to the end of the 20th century, which matches the "global dimming" and the subsequent "brightening" described for other regions in international scientific literature. The trend analysis applied to the IP series highlights a dominant decrease in SunD, with a negative and significant trend of about -0.6% per decade. These temporal variability and trends of the summer SunD in the IP are related to changes in the frequency of circulation patterns that were classified applying a Principal Component Analysis in T-Mode and then performing a Cluster Analysis on the most relevant extracted principal components, using a non-hierarchical k-means method as clustering algorithm. The analysis was carried out using the daily sea level pressure (SLP) data and the geopotential fields at 850 and 700 hPa, derived from the NCEP/NCAR reanalysis at a resolution of 2.5ºx2.5º, and in a selected area between 20°W-15°E longitude and 20º-45°N latitude. The results of the classification show that the most satisfactory results are those obtained with 12 circulation patterns. We calculated the time series of absolute frequency of occurrence of the above mentioned patterns, and correlated them with the summer SunD series. Four of these patterns are negatively and significantly correlated with the SunD series, while other four patterns are positively and significantly correlated. Grouping together the absolute frequency of the circulation patterns with positive significant correlation and those with negative significant correlation, the correlations increase to r=0.73 and r=-0.85, respectivaly. These two series of absolute frequencies are strongly and negatively correlated between them (r=-0.83), and show significant trends with opposite sign: -4.4 days and +2.6 days per decade, respectively. We completed the analysis using total cloud cover data over the 1961-2004 period, and data of TSP (total suspended particles) and PM10 (suspended particles <10 µm) from 14 air quality monitoring stations recorded in rural areas of Spain over the 1996-2004 period. The results show that the changes in the SunD over the IP can hardly be explained only by changes in the total cloud cover, and it is reasonable to affirm that there is also a contribution from the African dust episodes and resuspension processes in the incoming solar radiation that reach the IP, especially in the southern and central areas. Finally, we studied the relationship between SunD and Sahel rainfall variability measured by means of the Sahel index. There is a positive and significant correlation between the two variables, with the strongest values in the southern and central areas of the IP. The results suggest a possible link between the precipitation in the Sahel area and the SunD over the IP, due to an increase (decrease) in the dust intrusions and cloudiness during the years with negative (positive) anomalies of precipitation in the Sahel area.
A43B-1150
Using Surface Energy Balance Calculations of Rooftops to Generate Energy Efficient Buildings
Individual structures within the same urban region can experience different micro-scale (<103 m) climates as a consequence of their particular physical characteristics and surroundings. The energetics of these urban microclimates at length scales of individual structures are determined by a combination of different energy flux components that individually act to cool or heat the roof surface: long wave radiation, short wave radiation, sensible heat, evaporative cooling, leading to heat conduction into or out of the surface. In an analysis of rural and urban microclimates within the Chicago region, a semi- empirical energy balance model is used incorporating radiative and meteorological measurements to parameterize annual and diurnal variations in energy fluxes statistically. The temperature of the surface is determined by solving the heat conduction equation within the thickness of the building roof using a first principles mechanistic model. This allows comparisons of results between various surface types and microclimate conditions. Results show that the microclimates of the structures and modifications of surface and thermal properties influence their surface temperatures, adjacent air temperatures, and consequentially are shown to influence the heating or cooling loads throughout the year. Variations of these properties can significantly influence the distribution of energy amongst the fluxes acting on the roof to minimize heat conduction into the building, making them more energy efficient and also reduce the heat island effect.
A43B-1151
Annular Modes and the Poleward Movement of Subtropical Dry Zones
Projections of twenty-first century climate from the latest state-of-the-art climate models consistently call for a poleward expansion of the subtropical dry zones (SDZ) in response to increasing levels of atmospheric greenhouse gases. We find that approximately half of the model-simulated SDZ expansion during the next hundred years can be explained by positive trends in the Northern Hemisphere and Southern Hemisphere annular modes (NAM and SAM), implying a close connection between changes in the tropical and extratropical atmospheric circulation. The link between NAM and SAM variability and the SDZ expansion suggests that future changes in the hydrologic cycle are likely to be strongly influenced by atmospheric dynamics.
A43B-1152
Tropical Pacific Impacts of Convective Momentum Transport in the SNU Coupled GCM
Impacts of convective momentum transport (CMT) on tropical Pacific climate are examined, using an atmospheric GCM (AGCM) and coupled GCM (CGCM) from Seoul National University. The CMT scheme affects the surface mainly via a convection-compensating atmospheric subsidence which conveys momentum downward through most of the troposphere. AGCM simulations - with SSTs prescribed from climatological and El Nino Southern Oscillation (ENSO) conditions - show substantial improvements in circulation when CMT is added, such as an eastward shift of the climatological trade winds and west Pacific convection. The CMT also improves the ENSO wind anomalies by shifting them eastward and widening them meridionally, despite only subtle changes in the precipitation anomaly patterns. During ENSO, CMT affects the low-level winds mainly via the anomalous convection acting on the climatological westerly wind shear over the central Pacific - so that an eastward shift of convection transfers more westerly momentum toward the surface than would occur without CMT. By altering the low-level circulation, the CMT further alters the precipitation, which in turn feeds back on the CMT. In the CGCM, CMT improves the simulated climatology by shifting the mean convection and trade winds eastward and warming the equatorial SST; the ENSO period and amplitude also increase. In contrast to the AGCM simulations, CMT substantially alters the El Nino precipitation anomaly patterns in the CGCM. Also discussed are possible impacts of the CMT-induced changes in climatology on the simulated ENSO.
A43B-1153
Dynamical Impedances of Diurnal and Seasonal Horizontal Convections
The atmosphere of the earth is stable density-stratified fluid. Because the thermal response of land is different from that of sea, the differential heating causes horizontal convection. Horizontal convection consists of convergent and divergent fields. Typical examples of horizontal convection are land- and sea-breeze (diurnal cycle) and seasonal wind (annual cycle). There arenft any studies that examine the difference of dynamical feature of diurnal-cycle- and annual-cycle-horizontal convections. The purpose of this study is to examine the difference of dynamical feature of diurnal-cycle- and annual-cycle-horizontal convections using observational data. We characterize horizontal convection by two features: thermal skin depth and dynamical impedance. We define the ratio of pressure to temperature as thermal skin depth. The ratio of pressure to wind speed is dynamical impedance. To analyze observational data and extract the phenomenon that we are interested in, it is important that we should eliminate a basic flow. To eliminate the basic flow, we calculate flow convergence and divergence along closed circle because horizontal convection consists of convergent and divergent fields. The study area includes the four main islands of Japan. The Japanese Islands have 156 meteorological observation stations. Using the wind, pressure, and temperature data, we obtain the values of the thermal skin depths and the dynamical impedances. In diurnal-cycle-horizontal convection thermal skin depth is 600m in winter and 1500m in summer. In annual-cycle-horizontal convection thermal skin depth is 600m. In diurnal-cycle- and annual-cycle- horizontal convection dynamical impedance are 0.7 and 2 respectively. Stommel studied a steady convective motion under the condition that a gravitationally stable fluid was heated non-uniformly at the bottom (Stommel et al. 1957). This study and our results indicate that either diurnal-cycle- horizontal convection or annual-cycle-horizontal convection is not a steady flow at least. From the relationships between the diurnal variation of convergent and divergent flow and diurnal variations of solar radiation, temperature, pressure, and radiative cooling, it indicates that daily-cycle-horizontal convection is non-steady flow.
A43B-1154
Gravity wave in the lower stratosphere at South Pole
Using high-resolution balloon soundings from 2001 to 2005, the relationship between gravity wave (GW) sources over Antarctica and the strength of GW activity in the lower stratosphere at South Pole (SP) are investigated. A comprehensive analysis is performed for the GW energy density, vertical wavenumber spectra, and stability. The seasonal variation of GW energy of three altitude sections (10-15 km, 15-20 km, and 20-25 km) are compared. GW perturbations in the lowermost section are strongest in May and September, whereas in the altitude range of 15-25 km, strongest GW energy is observed only in September, which indicates that the dominant GW sources for May and September at 10-15 km may be different. The relationship between the GWs and the synoptic-scale variations in the troposphere and ageostrophic motions in the upper troposphere are examined using correlation and empirical orthogonal function (EOF) analysis. The time series of EOF1 of these two significant mechanisms of GW generation both have a minimum in austral summer when GW energy is also minimized. A ray-tracing model is applied to explore the seasonal variation of GW propagation condition due to the background field. During the summer, it is harder for waves to propagate into SP from lower latitude. Thus the minimum of GW energy in austral summer is attributed to the combination of weaker generation from synoptic activity, geostrophic adjustment and unfavorable background field for GW propagation.
A43B-1155
Present-day regional climate simulation of the North American and West African Monsoon: A comparative study
Predicting the climate variability in monsoon regions is a challenge for climate models. The realism of regional climate models (RCMs) depends on the quality of lateral boundary conditions (LBCs) and any systematic errors in the large-scale driving conditions will be added to the uncertainties of the model formulation. Here, we provide an attempt to quantify the systematic errors of an RCM in simulating monsoon systems by comparing simulations of the North American monsoon (NAM) and the West African monsoon (WAM). The purpose of the study is to discern whether the deficiencies arise from the model formulation or are due to dynamical problems. Using the Hadley Centre regional climate model HadAM3P at 50-km resolution, a pair of 22-year (1979-2002) simulations is conducted with the lateral boundary conditions from the NCEP-NCAR reanalysis R2 over North America and West Africa. The model validation focuses on precipitation and low level circulations at monthly, seasonal and interannual timescales. Result show that the RCM captures reasonably the basic features of NAM and WAM systems, but with different skills.
A43B-1156
Estimating climate model systematic errors in a climate change impact study of the Okavango River basin, southwestern Africa using a mesoscale model
Simulating the impact of future climate variability and change on hydrological systems requires estimates of climate at high spatial resolution compatible with hydrological models. Here we present initial results of a project to simulate future climate over the Okavango River basin and delta in Southwestern Africa. Given the significance of the delta to biodiversity and as a resource to the local population, there is considerable concern regarding the sensitivity of the system to future climate change. An important component of climate variability/change impact studies is an assessment of errors in the modeling suite. Here, we attempt to quantify errors and uncertainties involved in regional climate modelling that will impact on hydrological simulations. The study determines the ability of the MM5 Regional Climate Model to simulate the present day regional climate at the high resolution required by the hydrological models and the effectiveness of the RCM in downscaling GCM outputs to study regional climate change and impacts.
A43B-1157
Transition of SSMI Data to a Climate Data Record
Since 1993, the National Oceanic and Atmospheric Administration's (NOAA) National Climatic Data Center (NCDC) has served as the active archive of passive microwave satellite measurements from the Defense Meteorological Satellite Program's (DMSP) Special Sensor Microwave Imager (SSMI) instrument. SSMI data measurements have been used extensively to generate climate data sets (including rain, snow, ice, cloud liquid water, and total precipitable water) in support of both national and international programs. A project by NCDC and NOAA's Center for Satellite Applications and Research (STAR) is working towards the goal of regenerating a high quality SSMI Climate Data Record as defined by NOAA's Scientific Data Stewardship (SDS) program. As part of this effort, the SSMI Temperature Data Record (TDR) and Sensor Data Record (SDR) datasets have been reprocessed as value-added network Common Data Form (netCDF) orbit files. Data quality control flags embedded in netCDF orbit files preserve the original data, while warning users of erroneous geolocation, radiance and temporal values at the pixel level. These orbit files will also extend the period of record of SSMI data publicly available at NOAA's Comprehensive Large-Array Stewardship System (CLASS) by several years (August 1993-February 1997). Making earlier SSMI data available to customers and improving the quality of the SSMI dataset are important steps in attaining higher levels of dataset maturity in terms of scientific value and data preservation.
A43B-1158
Kelvin Waves in the Nonlinear Shallow Water Equations on the Sphere: Nonlinear Traveling Waves and the Corner Wave Bifurcation
The Kelvin wave is the lowest eigenmode of Laplace's Tidal Equation and is widely observed in both the ocean and the atmosphere. In this work, we neglect mean currents, but instead include the full effects of the earth's sphericity and the wave dispersion it induces. Through a mix of perturbation theory and numerical computations using a Fourier/Newton iteration/continuation method, we show that for sufficiently small amplitude, there are Kelvin traveling waves(cnoidal waves). As the amplitude increaes, the branch of traveling waves terminates in a so-called '' corner wave" with a discontinuous first derivative. All waves larger than the corner wave evolve to fronts and break. The singularity is a point singularity in which only the longitudinal derivative is discontinuous. As we solve the nonlinear shallow water equations on the sphere with increasing ε ('' Lamb's parameter"), dispersion weakens, the amplitude of the corner wave decreases rapidly, and the longitudinal profile of the corner wave narrows dramatically.