diurnal rainfall pattern observed by tropical rainfall measuring mission precipitation radar trmm pr around the indochina peninsula 1 this study addressed the diurnal cycle of rainfall during the summer monsoon season may to september around the indochina peninsula with a focus on the diurnal cycle s relationship to terrain the investigation used 10 year 1998 2007 tropical rainfall measuring mission precipitation radar trmm pr observations results revealed that the diurnal variations in rainfall over the indochina region had three distinct peaks an early afternoon maximum of rainfall occurred along the mountain ranges and on coastal land evening rainfall was observed near the foot of mountain ranges in a valley and in a basin shaped plain this rainfall weakened before the middle of the night heavy rainfall in the early morning was found around the coasts over the eastern gulf of thailand and the bay of bengal as well as over the eastern khorat plateau we found that nearly half of the total rainfall occurred in the early morning over these regions which indicated that early morning rainfall significantly contributes to the climatological rainfall pattern note that the regions with early morning heavy rain did not correspond to windward faces of mountains but to the windward plain or to an offshore area apart from the mountain ranges in the windward direction additional examination of rainfall frequency and rainfall intensity showed that this early morning heavy rainfall was composed of frequent or long lasting rainfall events with a strong intensity

development and formation mechanism of the southeast asian winter heavy rainfall events around the south china sea part i formation and propagation of cold surge vortex abstractexamination of the development of cold season heavy rainfall flood hrf events around the south china sea scs from their parent cold surge vortices csvs shows three new development processes first the formation mechanism of the parent csv of an hrf event csv hrf has a preference as to geographic location flow type of the cold surge inside the scs and time of day the surface trough east of the philippines taiwan and southern japan island chain in late fall and the near equator trough across borneo in winter facilitate the csv hrf formation in two regions the vicinity of the philippines and borneo the formation of the philippine borneo csv hrf occurs at 0600 utc 0000 utc with involvement from the philippine sea phs type scs type of cold surge flow second the flow type of the cold surge determines the csv hrf propagation across the south china sea the phs type scs type facilitates hinders the csv hrf westward propagation this occurs because the easterly northerly

numerical simulation of cyclone sidr using a cloud resolving model characteristics and formation process of an outer rainband abstractcyclone sidr one of the most devastating tropical cyclones that resulted in several thousand deaths and substantial damages developed in the north indian ocean and made landfall over the bangladesh coast on 15 november 2007 observation and simulation results show that sidr was embedded in a nonuniform environment and contained an intense outer rainband to the east of its center and a significant frontal band to the northwest a detailed study of the outer rainband is performed by numerical simulation the eastern band was a long quasi straight shape in the meridional direction that remained stationary relative to the cyclone center this band was composed of convective cells that developed southeast of the center within a synoptic scale convergence zone and propagated along the band toward the northeast quadrant the speed of the downwind propagating cells was greater than that of the cyclone which resulted in a convective cluster northeast of the center only the downwind portion of the band

the role of corsica in initiating nocturnal offshore convection in the region of corsica located in the western mediterranean sea the mean daily lightning activity as an indicator for deep convection in late summer and autumn shows a distinct maximum in mid afternoon and a secondary maximum at night during the night most of the lightning activity is located offshore and near the island s coastline currently there are no observational data which could be used to explain this nocturnal offshore convection but understanding its formation mechanism is important for accurately forecasting the regional weather in this article we explore two possible mechanisms initiating nocturnal offshore convection i convergence with subsequent lifting due to the interaction between drainage winds and the synoptic flow over the sea and ii dynamically induced lee side convergence due to the island barrier effect to this end we perform numerical simulations with the consortium for small scale modeling cosmo model at a convection permitting horizontal grid spacing of 2 8 km for two cases with different synoptic conditions and low level wind directions the simulation results show that the island s drainage flow can either favour or hinder the development of deep convection furthermore convective initiation is very sensitive to terrain elevation and model initialisation time and small changes of these parameters can determine whether deep convection can be successfully simulated

a linear theory of three dimensional land sea breezes abstractland sea breezes lsbs induced by diurnal differential heating are examined using a three dimensional linear model employing fast fourier transform with emphasis on the complex coastline shape and geometry the earth s rotation and background wind effects it has been demonstrated that the low level vertical motion associated with lsb can be significantly enhanced over a bay peninsula because of convergence of perturbations induced by differential heating along a seaward concave convex coastline the dependence of surface winds and vertical motion patterns and their evolutions on the coastline geometries such as the width and the aspect ratio of the bay the earth s rotation and the background winds are investigated the lsb induced by an isolated tropical island is characterized by onshore flow and ascent over the island in the afternoon to early evening with a reversal of direction from midnight to early morning the diurnal heating induced vertical motion is greatly enhanced over the isl

formation and maintenance of a long lived taiwan rainband during 1 3 march 2003 abstracttaiwan rainbands trs defined here as convective lines which form off the mountainous eastern coast of taiwan under weakly synoptically forced weather conditions are a well known mesoscale phenomenon but their formative processes remain the subject of debate this study uses surface and radar observations within the coastal zone of eastern taiwan and ncep reanalysis data to document a long lived tr with a lifetime of 36 h during 1 3 march 2003 to advance the current general understanding of mechanisms responsible for the tr s formation and maintenance detailed analyses indicate that the rainband was initiated by convergence that was produced as low level environmental northeasterly easterly onshore flow encountered topographically blocked northerlies that developed nearshore the northerly blocked flow was observed to weaken and subsequently dissipate because of changing synoptic pressure patterns that caused prevailing southeasterlies southerlies at low levels however colder nearshore ai

morning precipitation peak over the strait of malacca under a calm condition abstract this paper describes the formation mechanism of morning maximum in the diurnal cycle of precipitation at the strait of malacca under a calm condition with a nonhydrostatic mesoscale numerical model and ship based observational data the morning precipitation peak at the strait is induced by the convergence of two cold outflows that have been produced by the precipitation systems in the previous evening over sumatra and the malay peninsula the outflows converge at the strait of malacca around midnight a new precipitation system is thus generated and reaches its peak in the early morning sensitivity experiments using the numerical model suggest that the timing and position of the morning precipitation peak are affected by the width of the strait in the case of the strait of malacca its width favors the formation of the morning precipitation system around the center of the strait which explains why its diurnal cycle of precipitation can be observed much clearer than those in other coastal ar

winter monsoon convection in the vicinity of north borneo part i structure and time variation of the clouds and precipitation abstract radar and satellite observations in the vicinity of northern borneo obtained during the international winter monsoon experiment wmonex showed that the convection in that region underwent an extremely regular diurnal cycle over the sea to the north of borneo the general level of convective activity was increased during monsoon surges and during the passages of westward propagating near equatorial disturbances convective activity was decreased during monsoon lulls the diurnal cycle was well defined regardless of whether the general level of convective activity was enhanced or suppressed by synoptic scale events the cycle of convection over the sea was especially well documented it was typically initiated at about midnight when an offshore low level wind began where this wind met the monsoonal northeasterly flow usually just off the coast convective cells formed after midnight the convection continued to develop and by 0800 lst it had evolved into an organized mesoscale system with a

organization of oceanic convection during the onset of the 1998 east asian summer monsoon the organizational modes of convection over the northern south china sea scs during the onset of the summer monsoon are documented using radar and sounding data from the may june 1998 south china sea monsoon experiment scsmex the onset occurred in mid may with a rapid increase in deep convection over a 10 day period accompanied by a major shift in the circulation over the east asian region analysis of bureau of meteorology research centre bmrc radar data from dongsha island reveals a wide range of organizational modes of convection over the northern scs proximity sounding data indicate that lower and middle level vertical wind shears exerted a dominant control over the orientation of convective lines within mesoscale convective systems in this region as has been found in the australian monsoon region and the equatorial western pacific the results are consistent with the conceptual model of lemone et al based on the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare except two new organizational modes have been identified shear parallel bands for strong low level shear and weak midlevel shear when there is weak instability and the air is dry aloft and shear parallel bands for strong shears in both layers when the shear vectors are in the same direction midlatitude influences namely the passage of troughs over southern china likely contributed to these two additional modes the stratiform rain fraction from the convective systems during the monsoon onset period was relatively small 26 compared to the estimated average of about 40 for the entire tropics this small fraction is attributed to the weak instability during the onset period and relatively dry air in the upper troposphere

role of orography diurnal cycle and intraseasonal oscillation in summer monsoon rainfall over the western ghats and myanmar coast abstractrainfall over the coastal regions of western india western ghats wg and myanmar arakan yoma ay two regions experiencing the heaviest rainfall during the asian summer monsoon is examined using a tropical rainfall measuring mission trmm precipitation radar pr dataset spanning 16 years rainfall maxima are identified on the upslope of the wg and the coastline of ay in contrast to the offshore locations observed in previous studies continuous rain with slight nocturnal and afternoon evening maxima occurs over the upslope of the wg while an afternoon peak over the upslope and a morning peak just off the coast are found in ay resulting in different locations of the rainfall maxima for the wg upslope and ay coastline large rainfall amounts with small diurnal amplitudes are observed over the wg and ay under strong environmental flow perpendicular to the coastal mountains and vice versa composite analysis of the boreal summer intraseasonal oscillation bsiso shows that the rain an

deep convective systems observed by a train in the tropical indo pacific region affected by the mjo abstractin the indo pacific region mesoscale convective systems mcss occur in a pattern consistent with the eastward propagation of the large scale convective envelope of the madden julian oscillation mjo mcss are major contributors to the total precipitation over the open ocean they tend to be merged or connected systems while over the maritime continent area they tend to be separated or discrete over all regions affected by the mjo connected systems increase in frequency during the active phase of the mjo characteristics of each type of mcs separated or connected do not vary much over mjo affected regions however separated and connected mcss differ in structure from each other connected mcss have a larger size and produce less but colder topped anvil cloud for both connected and separated mcss larger systems tend to have colder cloud tops and less warmer topped anvil cloud the maximum height of mcs precipitating cores varies only slightly and the variation is related to sea surface t

500 mb winter variability over the antarctic palmer peninsula winter time variability of heights over the antarctic peninsula weddell sea and queen maud land are shown to have important contributions from correlations between the zonally averaged height field z and longitudinally asymmetric motions this is different from what it is observed at other longitudes where the time variance can be explained in terms of variance of the zonally averaged fields plus the variance of deviations from zonal averages it is shown that when z is larger than its winter average a pattern with southerlies over the weddell sea at 500 mb and northerlies over eastern antarctica develops south of 60 s these southerlies are found displaced about 15 northward with episodes of meridional wind magnitudes over eastern antarctica larger than 2 m s the equivalent barotropic structure of southern hemisphere tropospheric long waves justify extension of the 500 mb results presented here to higher levels recent measurements taken by the airborne antarctic ozone experiment in the upper troposphere and lower stratosphere 10 to 18 km above sea level have detected the presence of ozone depleted air over the antarctic peninsula and weddell sea it is conjectured here that this may be partly due to the transport of ozone poor air from high latitudes into this region

mean state of the troposphere over south east asia and the east indies december 1978 the mean state of the troposphere over south east asia from 8 30 december 1978 is described in the lower troposphere a jet was observed over the south china sea extending south westward from the philippines evidence suggests that this north easterly jet was supported by downstream blocking induced by the borneo land mass at the equator the jet had the appearance of being channelled between the highlands of borneo and sumatra on its left flank near the west coast of borneo was a semi permanent and quasi stationary vortex being warm core this vortex was probably maintained in part by latent heat release in cumulus convection by partitioning the data into means at 00 and 12 gmt the intensity of the rising branch of the hadley circulation over borneo was shown to increase by a factor of two from 100 10 5 to 200 10 5mb s 1 from 00 to 12 gmt

seismotectonics of the himalayan collision zone geometry of the underthrusting indian plate beneath the himalaya fault plane solutions and well determined focal depths of medium sized earthquakes topography and landsat imagery in conjunction with seismicity maps cross sections and available geological information are used to investigate the present tectonics of the himalayan continental collision zone most of the accurately located epicenters of events along the himalayan arc 78 e 95 e that occurred between 1961 and 1981 are concentrated in a narrow zone about 50 km wide lying between the northerly dipping main boundary mbt and main central mct thrusts most of these events are located just south of the mct though the epicenters of the events are in general well located their depths as determined by teleseismic travel time data are very unreliable events with accurately determined depths obtained from identification of surface reflected phases define a simple planar zone from about 10 km and 20 km depth with an apparent dip of about 15 this result is all the more remarkable considering that the events used were located along about an 1800 km length of the himalyan arc except for one all available focal mechanisms of events within this zone indicate shallow 30 north dipping thrusts this shallow north dipping zone apparently defines a part of the detachment that separates the underthrusting indian plate from the lesser himalayan crustal block the spatial extent and the geometry of this interplate thrust zone strongly indicate that the mbt and nearby subsidiary surface and blind thrusts rather than the mct are currently the most active structures of the himalayan arc we suggest that the great himalayan earthquakes m 8 occur along the same detachment surface as defined by the thrust type medium sized events events located to the south of the mbt and beneath the ganges foredeep show normal faulting with t axes perpendicular to the himalayan trend the above results suggest that the indian continental plate is underthrusting the himalayan crustal blocks in a relatively coherent and simple geometry and that this geometry is not much different from that observed along oceanic subduction zones the november 19 1980 earthquake that occurred near the mct near 88 5 e shows a predominantly strike slip focal mechanism one of the nodal planes of this mechanism is transverse to the himalayan structural grain and moreover this plane has a trend similar to that of the recently mapped yadong gulu rift in the tethyan himalaya and in southern tibet just northeast of the earthquake we interpret this predominantly left lateral strike slip mechanism to indicate a possible genetic relationship between transverse structural features in the underthrusting indian plate the kishangang basement fault and the upper himalayan blocks and tibet

convectively forced diurnal gravity waves in the maritime continent abstractlong lived zonally propagating diurnal rainfall disturbances are a highly pronounced and common feature in the maritime continent mc a recent study argues that these disturbances can be

squall lines and convectively coupled gravity waves in the tropics why do most cloud systems propagate westward abstractthe coupling between tropical convection and zonally propagating gravity waves is assessed through fourier analysis of high resolution 3 hourly 0 5 satellite rainfall data results show the familiar enhancement in power along the dispersion curves of equatorially trapped inertia gravity waves with implied equivalent depths in the range 15 40 m i e pure gravity wave speeds in the range 12 20 m s 1 here such wave signals are seen to extend all the way down to zonal wavelengths of around 500 km and periods of around 8 h suggesting that convection wave coupling may be important even in the context of mesoscale squall lines this idea is supported by an objective wave tracking algorithm which shows that many previously studied squall lines in addition to 2 day waves can be classified as convectively coupled inertia gravity waves with the dispersion properties of shallow water gravity waves most of these disturbances propagate westward at speeds faster than the background flow to under

dynamical influence of the tibetan plateau on the winter monsoon over southeastern asia 1 previous studies have shown 1 that the tibetan plateau produces a significant fraction of the two components of the equatorial mountain torque emt in winter 2 that these torques are in part related to the east asian cold surges and 3 that the cold surges affect the convection over the maritime continent we show here that these relations are strong enough for the convection over the equatorial south china sea to be associated with significant signals on the two components of the emt that can precede by a few days and more the convection these signals are associated to surface pressure and temperature patterns that are strongly reminiscent of the east asian cold surges our results therefore show that the tibetan plateau couple dynamically the midlatitudes and the tropical region and that the vectors of this dynamical coupling are the cold surges this coupling also influences the convection over the northern bay of bengal mainland southeast asia and indonesia

mechanism of the northward propagation of mesoscale convective systems observed on 15 june 2005 during palau2005 1 this paper describes the structure and evolution of northward propagating mesoscale convective systems mcss observed over the tropical western pacific on 15 june 2005 a wedge shaped convective cloud area consisting of three groups of mcss was generated near the equator to the north of new guinea at around 0000 lst on 15 june and one of the groups of mcss propagated toward palau 7 8 n dropsonde analysis revealed that the mcss developed at the northern edge of a cold air mass that had a horizontal scale of more than 400 km global objective analysis data from the japan meteorological agency showed that the cold air mass observed by the dropsonde analysis originated in a land breeze from new guinea the cold air mass was initially formed by cold advection from the south and was maintained by cooling with the mcss when the initial mcss were generated along the land breeze front an easterly wave which was accompanied by low level southerly wind and a low pressure area was located near palau the cold air mass associated with the land breeze between 132 and 137 e was locally extended toward the center of the low pressure area the results suggest that the easterly wave located around palau helped locally promote northward cold advection from new guinea inducing the long distance northward propagation of mcss generated along the land breeze front

diurnal patterns of rainfall in northwestern south america part i observations and context one of the rainiest areas on earth the panama bight and pacific western littoral of colombia is the focal point for a regional modeling study utilizing the fifth generation pennsylvania state university ncar mesoscale model mm5 with nested grids in this first of three parts the observed climatology of the region is presented the seasonal march of rainfall has a northwest southeast axis with western colombia near the center receiving rain throughout the year this study focuses on the august september season the diurnal cycle of rainfall over land exhibits an afternoon maximum over most of south and central america typically composed of relatively small convective cloud systems over some large valleys in the andes and over lake maracaibo a nocturnal maximum of rainfall is observed a strong night morning maximum of rainfall prevails over the coastal ocean propagating offshore and westward with time this offshore convection often takes the form of mesoscale convective systems with sizes comparable to the region s coastal concavities and other geographical features the 10 day period of these model studies 28 august 7 september 1998 is shown to be a period of unusually active weather but with a time mean rainfall pattern similar to longer term climatology it is concluded that the rain producing processes during this time period are likely to be typical of those that shape the seasonal climatology

global variability of mesoscale convective system anvil structure from a train satellite data abstract mesoscale convective systems mcss in the tropics produce extensive anvil clouds which significantly affect the transfer of radiation this study develops an objective method to identify mcss and their anvils by combining data from three a train satellite instruments moderate resolution imaging spectroradiometer modis for cloud top size and coldness advanced microwave scanning radiometer for earth observing system amsr e for rain area size and intensity and cloudsat for horizontal and vertical dimensions of anvils the authors distinguish three types of mcss small and large separated mcss and connected mcss the latter are mcss sharing a contiguous rain area mapping of the objectively identified mcss shows patterns of mcss that are consistent with previous studies of tropical convection with separated mcss dominant over africa and the amazon regions and connected mcss favored over the warm pool of the indian and west pacific oceans by separating the anvil from the raining regions of

convection in gate the difficult problem of parameterizing tropical convection in large scale models of the atmosphere led to the global atmospheric research program s atlantic tropical experiment gate whose goal was to improve basic understanding of tropical convection and its role in the global atmospheric circulation a dense network of instrumented ships equipped with upper air sounding equipment and quantitative weather radars were located over the atlantic ocean in the intertropical convergence zone itcz just west of equatorial africa the ship network was supplemented by a fleet of research aircraft and a geosynchronous meteorological satellite the data obtained show that the deep convection in the itcz was concentrated in two types of cloud clusters rapidly moving squall clusters and slowly moving nonsquail clusters the clusters were characterized by large mid to upper level cloud shields or anvil clouds that emanated from penetrative cumulonimbus convection accompanying the deep cumulonimbus in each cluster was a log normal spectrum of smaller convective features ranging from moderate cumulonimbus down to tiny nonprecipitating cumulus the large cumulonimbus were typically grouped within a cluster into one or more mesoscale precipitation features or mpf s which were apparently triggered in mesoscale regions of intensified low level convergence as an mpf matured it developed a region of stratiform precipitation adjacent to its active deep convective cells the stratiform precipitation fell from the anvil cloud associated with the stratiform precipitation were a mesoscale downdraft below the anvil cloud and an apparent mesoscale updraft within the anvil cloud itself above the mesoscale downdraft these mesoscale drafts were distinct from the convective scale updrafts and downdrafts of the cumulus and cumulonimbus cells of the cluster downdrafts both convective scale and mesoscale filled the planetary boundary layer in the vicinity of cumulonimbus with stable air of low moist static energy these wakes of downdraft air exerted a strong control on where future convection broke out the results of gate show that to simulate the effects of tropical convection in large scale numerical models of the atmosphere a variety of phenomena must be accounted for including not only convective scale updrafts and downdrafts but anvil clouds with mesoscale updrafts and downdrafts downdraft induced boundary layer transformations and mesoscale convergence patterns experimentation with ways of including some of these features of tropical convection in large scale diagnostic and prognostic studies is under way but much work remains to be done

sea breeze circulation over jakarta indonesia a climatology based on boundary layer radar observations abstract characteristics of sea breeze circulation over the tropical site of jakarta indonesia have been documented based on analyses of satellite images and data from long term l band boundary layer radar measurements carried out at serpong 6 4 s 106 7 e inspection of satellite imagery reveals that a sea breeze front develops well along the northern coastal plain of west java and propagates inland until its structure is deformed over complex topography it is found that the sea breeze signal detected by the boundary layer radar is most well defined during the dry season months of july october in all of these months radar observations indicate a late afternoon intensification of sea breeze flow in the 0 5 0 8 km height range between 1700 and 1800 lt which is not elucidated upon by surface measurements the effect of weather conditions on the sea breeze pattern is investigated by using a cloudiness index derived from data of incoming solar radiation the results show that sea breeze intrusion over

why precipitation is mostly concentrated over islands in the maritime continent abstract high resolution observations and regional climate model simulations reveal that precipitation over the maritime continent is mostly concentrated over islands analysis of the diurnal cycles of precipitation and winds indicates that this is predominantly caused by sea breeze convergence over islands reinforced by mountain valley winds and further amplified by the cumulus merger processes comparison of a regional climate model control simulation to a flat island run and an all ocean run demonstrates that the underrepresentation of islands and terrain in the maritime continent weakens the atmospheric disturbance associated with the diurnal cycle and hence underestimates precipitation the implication of these regional modeling results is that systematic errors in coarse resolution global circulation models probably result from insufficient representation of land sea breezes associated with the complex topography in the maritime continent it is found that precipitation in the maritime continent

statistical location and timing of the convective lines off the mountainous coast of southeastern taiwan from long term radar observations in this study observations from the c band doppler radar on green island which is located off the southeastern coast of taiwan during 1998 2004 were analyzed to investigate the statistical characteristics of the convective lines occurring off the mountainous coast of southeastern taiwan with emphasis on their formative location and timing a total of 211 cases of the lines were identified during the study period it is shown that the lines were clearly a year round phenomenon and five cases occurred per month on average statistical analyses for all identified cases reveal that the formative area of the lines was extended substantially from nearshore regions to at least 100 km offshore with the region of the most frequent formation primarily confined to an elongated zone located 30 km off the coast along coast variations of line formation were also evident and were shown to be closely related to the nearshore terrain features the lines tended to form more frequently during the nighttime hours than the daytime hours with a formative peak between 2000 and 2200 lst minimum formation was found near noon between 1200 and 1400 lst however considerable cases still could be found during the late morning and late afternoon hours more than 70 of the lines 150 cases had a duration of less than 4 h and the mean duration for all lines was calculated to be 3 5 h in addition this study also documented statistical differences in the formative and flow characteristics between the nearshore and offshore lines which are distinguished by offshore distances of formative location that are less or greater than 40 km respectively of particular note the analyses presented strongly suggest that the physical mechanisms contributing to the initiation of the nearshore and offshore lines are fundamentally different

formation of the convective lines off the mountainous coast of southeastern taiwan a case study of 3 january 2004 abstract convective lines frequently occurring off the mountainous coast of southeastern taiwan under weakly synoptically forced weather conditions are one of the most well known mesoscale phenomena in taiwan these lines usually develop close to the coast but frequently can also be observed well offshore while nearshore lines are better understood the formative processes of the offshore lines remain unclear the main objective of this study is to use various available observations e g doppler radar surface and sounding observations quikscat and ncep data collected over southeastern taiwan to investigate a specially chosen case on 3 january 2004 in an attempt to identify possible mechanisms leading to the formation of the offshore lines the studied line was formed 50 60 km away from the southeastern coast of taiwan and oriented south southwest to north northeast and approximately parallel to the coast detailed analyses of the event indicated that the formation of the line did not appear direc

effects of the cold tongue in the south china sea on the monsoon diurnal cycle and rainfall in the maritime continent we investigate the effects of the cold tongue in the south china sea scs on the winter monsoon rainfall and diurnal cycle in the maritime continent using a numerical model verified with satellite rainfall and reanalysis data composite analysis of the observation and reanalysis data based on cold tongue index indicates that the penetration of the monsoon to java sea is enhanced when the cold tongue is strong a sensitivity experiment without the cold tongue shows that the winter monsoon is diminished over scs and around coastal regions because of anomalous low level cyclonic circulation associated with enhanced convection over scs due to the warmer sea surface temperature sst the diurnal cycle in particular the night morning rainfall over the sea in coastal regions is modified the effect on daytime rainfall over the land is relatively weaker along the northern coast of java far from the scs the night morning rainfall is much reduced over the java sea when the cold tongue is suppressed because of the weakened land breeze front as a result of the weakened northerly monsoon in contrast the afternoon evening rainfall on java island is slightly enhanced showing that the local impacts are not simply the result of large scale subsidence from the convective anomaly in the scs along the northwestern coast of borneo adjacent to the scs the weakened winter monsoon tends to reduce the rainfall at the land breeze front near the coastline on the other hand the warmer sst forces a stronger land breeze and the weakened monsoon encourages further and faster offshore propagation of the land breeze front consequently the rainfall peak shifts further offshore in the sensitivity experiment we conclude that the cold tongue has two effects the sustenance of a strong monsoon indirect effect and the cooling of local sst direct effect which have opposite influences on the diurnal cycle in the maritime continent

interpretation of observed ground level changes due to the 1905 kangra earthquake northwest himalaya the kangra earthquake of 1905 in the northwest himalaya was the first indian earthquake for which coseismic ground elevation changes were measured through repeat precision levelling the levelling une from saharanpur to mussoorie via dehra dun was situated near the southeastern extremity of the nw se trending meizoseismal area maximum uplift of 14 3 cm was measured at a bench mark in dehra dun some details of the levelling data having been published recently data for eight bench marks were considered for interpretation in this study in principle these are sufficient for us to estimate eight parameters of a rectangular rupture buried in a homogeneous poisson solid but because of some uncertainties regarding the bench mark positions and also the relatively small amounts of uplift measured at the bench marks we have preferred to use the data as a means to check the reasonableness of rupture models proposed on other grounds rather than to propose a new model independently the observed elevation changes are not in accord with the view that the kangra earthquake was caused by a single 100 km long rupture along the shahpur mandi sector of the northwest himalaya however the data can be explained if in addition a second smaller rupture extending on either side of the levelling une near dehra dun is assumed the data can also be explained if the rupture during the earthquake had 1 a length of 280 km parallel to the general strike of the himalaya from around kangra up to a short distance about 10 15 km northwest of the levelling une near dehra dun 2 a breadth of 80 km perpendicular to the strike of the himalaya 3 a northeasterly dip of about 5 and 4 a depth of 10 15 km along its sw edge finally the elevation data rule out any role for the main boundary thrust in the occurrence of the kangra earthquake this major tectonic feature demarcating the geological boundary between the outer and the lesser himalaya thus appears to be unimportant in the current seismotectonics of the region and the subduction of the indian lithospheric plate under the mountains

regional seasonal and diurnal variations of extreme convection in the south asian region abstract temporal and spatial variations of convection in south asia are analyzed using eight years of tropical rainfall measuring mission trmm precipitation radar pr data and ncep reanalysis fields to identify the most extreme convective features three types of radar echo structures are defined deep convective cores contiguous 3d convective echo 40 dbz extending 10 km in height represent the most vertically penetrative convection wide convective cores contiguous convective 40 dbz echo over a horizontal area 1000 km2 indicate wide regions of intense multicellular convection and broad stratiform regions stratiform echo contiguous over an area 50 000 km2 mark the mesoscale convective systems that have developed the most robust stratiform regions the preferred locations of deep convective cores change markedly from india s east coast in the premonsoon to the western himalayan foothills in the monsoon they form preferentially in the evening and over land as near surface moist flow is cap

diurnal cycle of the itcz in dynamo abstractduring the 2011 special observing period of the dynamics of the madden julian oscillation dynamo field experiment two sounding arrays were established over the central indian ocean one

a case study of the borneo vortex genesis and its interactions with the global circulation 1 during the east asian winter or the northeast monsoon november march cold surges associated with cold air outbreaks from the siberian high propagate equatorward and interact with the near equatorial trough in the southern south china sea usually in the later phase of the monsoon the so called borneo vortex develops over the sea and is the main driver for the formation of deep convection and heavy rainfall in east malaysia we present a case study of a cold surge induced event during january 2010 we diagnose a substantial export of potential energy from the borneo vortex strengthening the subtropical jet at 200 hpa the velocity potential maximum related to the established hadley circulation is shifted eastward from 140 e toward the dateline from presurge to postsurge periods this modifies the general circulation patterns in the southern hemisphere with possible consequences for trace gas distributions in addition we explore implications for vertical transport by deep convection occurring in association with the borneo vortex by diagnosing potential vorticity changes in the vicinity of the vortex

time space characteristics of diurnal rainfall over borneo and surrounding oceans as observed by trmm pr abstract five years of tropical rainfall measuring mission trmm precipitation radar pr data were used to investigate the time and space characteristics of the diurnal cycle of rainfall over and around borneo an island in the maritime continent the diurnal cycle shows a systematic modulation that is associated with intraseasonal variability in the large scale circulation pattern with regimes associated with low level easterlies or westerlies over the island the lower tropospheric westerly easterly components correspond to periods of active inactive convection over the island that are associated with the passage of intraseasonal atmospheric disturbances related to the madden julian oscillation a striking feature is that rainfall activity propagates to the leeward side of the island between midnight and morning the inferred phase speed of the propagation is about 3 m s 1 in the easterly regime and 7 m s 1 in the westerly regime propagation occurs over the entire island causing a leeward enhan

space time structure of rain rate fields information on the spatial and temporal statistics of rain rate is needed for the design of remote sensing systems for the measurement of areal rainfall accumulation and for the design of millimeter wave communication systems in this study rain gage and radar data were used to determine empirically the spatial and temporal structure of the rain process as observed using rain rate as a tracer of the atmospheric motions and to test the validity of taylor s hypothesis for relating their spatial and temporal statistics weather radar derived rain rate maps were employed to obtain one and two dimensional spatial power spectra azimuthally averaged two dimensional spectra displayed the shape predicted for a passive scalar advected by a steady state field of two dimensional turbulence driven by the input of energy over a narrow band of wave numbers one dimensional spatial spectra for a short line of rain gages had the same spectral shape as the azimuthally averaged spectra obtained from the radar data temporal spectra from the gage time series were nearly identical in shape to the one dimensional spatial spectra if less than a half hour of data were processed to generate a spectrum and a constant translation velocity was assumed to relate themore temporal and spatial scales for spectra corresponding to longer durations a match could not be made less

the diurnal cycle of tropical convection the diurnal cycle of tropical convection is investigated with global cloud imagery constructed from 11 m radiance measurements taken aboard six satellites four harmonics of the diurnal cycle are resolved in the cloud imagery with about 50 km horizontal resolution to isolate deep convective activity from other processes which cause diurnal fluctuations in longwave radiance an index of deep convective activity is constructed by thresholding to brightness temperatures less than 230 k significant diurnal amplitude of deep convection is found only over tropical landmasses over the tropical oceans the diurnal cycle is weak and is barely discernible from the background red spectrum of convective variance nonetheless oceanic convection exhibits a systematic diurnal fluctuation with maximum intensity in the early morning nocturnal subsidence along the cloud free equator is postulated to play a role in forcing diurnal variation in the intertropical convergence zones other mechanisms are also implied to contribute as a similar early morning maximum in deep convection is seen even where no adjoining cloud free regions occur the diurnal cycle of deep convection is found to be organized on planetary scales predominantly in nonmigrating modes i e modes with phase speeds not equal to that of the sun the nonmigrating modes are postulated to be produced by the nonuniform distribution of convective centers the nonmigrating zonally symmetric component is found to be especially large while the role of this mode in forcing diurnal variations of the tropospheric circulation e g the hadley cell is questionable its role in modulating the ionospheric electric potential is well established discrepancies with the traditional notion that cloud to ground lightning is the dominant mechanism by which the earth is negatively charged are discussed in particular the probable role of nonlightning producing clouds e g the stratiform portion of convective complexes in diurnally modulating the negative charge on earth is discussed

contrasting characteristics of convection over the northern and southern south china sea during scsmex observations from two enhanced sounding arrays during the may june 1998 south china sea monsoon experiment scsmex are used to determine and contrast the properties of convection over the northern and southern south china sea scs a regression analysis between sst data and monthly rainfall indicates that the enso signal exerted a strong influence on the rainfall distribution over the scs during scsmex this resulted in wetter than normal conditions along the south china coast and northern scs and generally drier than average conditions elsewhere particularly over the philippine islands the monsoon onset as determined by a shift in the low level winds from easterly to southwesterly over the scs occurred around mid may over the southern enhanced sounding array sesa the onset was characterized by a rainy period associated with the passage of a convectively coupled kelvin wave this was followed by a weeklong break and then several episodic rain events with increasingly higher rain rates rainfall over the northern enhanced sounding array nesa which was largely out of phase with sesa rainfall events occurred primarily during two 10 day periods separated by a weeklong break convective characteristics over the sesa deduced primarily from heat and moisture budget profiles indicate a high stratiform rain fraction consisting of alternating periods with decaying mesoscale systems that organized near the western borneo coastline and shallower convective clouds in contrast nesa averaged profiles were indicative of deep convection with a relatively small stratiform rain fraction which was confirmed with radar analyses during the onset convective period the diurnal cycle of convection is a dominant feature throughout much of the scs over both budget regions early morning 0500 0800 lt convective systems were frequently initiated near the coasts then gradually dissipated during the course of the day as the midlevel steering currents moved the systems away from the coastline these decaying convective systems resulted in an early afternoon 1400 lt rainfall peak over both sonde arrays

barrier effect of the indo pacific maritime continent on the mjo perspectives from tracking mjo precipitation abstractexplanations for the barrier effect of the indo pacific maritime continent mc on the mjo should satisfy two criteria first they should include specific features of the mc namely its intricate land sea distributions and elevated terrains second they should include mechanisms for both the barrier effect and its overcoming by some mjo events guided by these two criteria a precipitation tracking method is applied to identify mjo events that propagate across the mc mjo c and those that are blocked by the mc mjo b about a half of mjo events that form over the indian ocean propagate through the mc most of them 75 become weakened over the mc the barrier effect cannot be explained in terms of the strength horizontal scale or spatial distribution of mjo convection when it approaches the mc from the west a distinction between mjo b and mjo c is their precipitation over the sea versus land in the mc region mjo c events rain much more over the sea than over land whereas rainfall over

observed structure of mesoscale convective systems and implications for large scale heating mesoscale convective cloud systems that produce large amounts of rain in mid latitudes and most of the rain in the tropics consist of a combination of convective and stratiform cloud the convective regions contain numerous deep cells that are often but not always arranged in lines the stratiform region is an outgrowth of the convective ensemble it lies adjacent to the convective region and is seeded by ice particles detrained from convective towers sometimes it lies to the rear of a propagating convective line while on other occasions it surrounds the convection the heating of the large scale environment by a mesoscale convective system is affected by both the convective and stratiform regions although processes such as melting and radiation are important the net heating by a system is dominated by condensation and evaporation associated with vertical air motions this paper reviews recent observational evidence regarding the mean vertical motion profiles in the convective and stratiform regions of mesoscale convective systems and the implications of these mean motions for the vertical distribution of heating of the large scale environment in both the convective and the stratiform regions vertical motions have been determined by various techniques including composites of rawinsonde and aircraft wind data single and dual doppler precipitation radar analyses and wind profiler observations in stratiform regions these data consistently show mean vertical velocity that is upward in the upper troposphere and downward in the lower troposphere the level separating upward from downward motion is located from 0 to 2 km above the 0 c level depending on location within the stratiform region diagnostic calculations show that these vertical motion profiles imply heating of the upper troposphere and cooling of lower levels by stratiform region processes data on vertical motions in the convective regions are less consistent from case to case these data sometimes indicate that the mean vertical velocity in convective regions is maximum in the lower troposphere in other cases the data indicate a maximum in the high troposphere diagnostic calculations show that heating profiles diagnosed from these two types of profile are quite different the first having a maximum of heating in the lower troposphere while the second has a maximum in the middle troposphere although it is difficult to determine whether or not the differences in estimates arise from different types of observations analysis methods or sampling strategies it seems likely that they stem from differences in the large scale environment of the different mesoscale systems the ubiquitous occurrence of stratiform regions in mesoscale convective systems and hurricanes together with their consistent heating profiles which systematically concentrate heating in upper levels while cooling lower levels are a major consideration in evaluating the interaction of mesoscale systems with the large scale environment however the consistency of the stratiform profiles from case to case indicates that the variability of net convective plus stratiform heating profiles from case to case lies primarily in the variation of the convective region profiles from one case to another it is suggested that future work should focus on the convective region vertical profiles of vertical motion and heating and on the large scale environmental factors that may control the variation of these profiles from case to case

radar observations of the diurnally forced offshore convective lines along the southeastern coast of taiwan this study documents offshore convective lines along the southeastern coast of taiwan a frequent but poorly understood mesoscale phenomenon that influences coastal weather during the taiwan mei yu season doppler radar and surface observations were gathered from a specially chosen period 11 15 may 1998 when the offshore convective lines were active off the southeastern coast of taiwan these observations were used to show the basic character structure and possible formative processes of offshore convective lines the synoptic environment accompanying these events was found to be relatively undisturbed and featured uniformly prevailing southerly south southeasterly winds in the boundary layer with southwesterlies westerlies aloft examination of radar data during the study period indicates that the lines generally occurred 10 30 km offshore and were characterized by an elongated narrow zone 5 10 km wide of heavy precipitation the lines were oriented roughly parallel to the coastline and generally did not move significantly the intensity of the radar reflectivity associated with the lines exhibited a marked diurnal variation and was closely related to the coastal offshore flow developing at night detailed analyses of an event on 14 15 may 1998 further show the important physical link between the offshore flow and the development of the line the offshore line was found to be located near and immediately ahead of the seaward extent of the offshore flow particularly a very narrow zone 2 km of low level heavy precipitation 40 45 dbz coincided with regions of strong updrafts and convergence where the prevailing southerly onshore flow encountered the cool offshore flow nearshore this offshore flow induced convergence given a stable thermodynamic condition in the lowest 1 km in the inflow region was a crucial low level forcing that provided lifting to trigger moist deep convection in this case the line s precipitation tilt eastward was confined primarily to the warmer inflow side rather than feeding the offshore flow to the west of the line no consistent upshear tilt of updrafts throughout the storm layer was observed which is consistent with the presence of a strong westerly shear in the line s environment both of these observations explain a relatively strong weak modification of low level onshore offshore flow by precipitation additionally a combination of surface and doppler radar observations indicates that the leading edge of the offshore flow moved seaward very slowly at 0 7 m s 1 and possessed a frontal character with notable discontinuities in near surface wind and temperature instead of pressure and dewpoint temperature

diurnal forcing and phase locking of gravity waves in the maritime continent abstractan unfiltered zonal hovmoller depiction of rainfall in the maritime continent mc reveals remarkable spatiotemporal continuity of zonally propagating disturbances with a diurnal period wh

an analysis of tropical cyclone formations in the south china sea during the late season abstractthis study examines tropical cyclone tc formations in the south china sea scs associated with the strong northeasterly monsoon during the late season results show that the percentage of all vortices that develop to tc intensity is lower in the late season when compared to that associated with the mei yu front in may and june but the average formation time for the late season cases is significantly shorter than that for the mei yu frontal cases composite analyses show that the formation cases in the late season have larger low level vorticity and upper level divergence as well as higher 700 hpa relative humidity when compared to the nonformation cases another major difference between the formation and the nonformation cases is the low level northeasterlies to the north or upstream of the incipient disturbance which weakens right before the pre tc disturbance reaching 25 kt 13 m s 1 the weakening of the northeasterlies may be important to tc formation because it decreases the vertical

tropical rainfall measuring mission observation and regional model study of precipitation diurnal cycle in the new guinean region 1 the diurnal cycle of precipitation in the new guinean region is studied on the basis of satellite observations from tropical rainfall measuring mission trmm precipitation radar pr measurements and regional atmospheric model simulations the study focuses on the effects of both the land sea breeze and the orographic forcing on the diurnal evolution of precipitation during the rainy season january march in the region the 7 year trmm pr data composite reveals several distinct features of the precipitation diurnal cycle in the region precipitation bands develop in the inland coastal region in the late morning to early afternoon and migrate inland from both northeast and southwest sides of the new guinean island following the inland penetration of the sea breeze fronts a separate convective rainband develops over the central mountain ridge in the early afternoon as a result of the development of the upslope winds due to the elevated surface warming over the mountain in the morning hours this mountain ridge rainband intensifies and becomes the dominant rainband as the coastal rainbands associated with the sea breeze fronts weaken during the late afternoon and the early evening in the midnight to the early morning the rainband over the mountaintop weakens as downslope winds develop and splits into two rainbands propagating away from the mountain ridge one to the north and one to the south and weakens over the lowland some distance away from the coasts meanwhile a coastal rainband develops offshore on each side of the island in the late evening to midnight and remains strong through early morning before it migrates offshore as a result the rainfall rate peaks in the late afternoon to early evening in most land areas except for in the lowland regions between the coastlines and the mountain where the rainfall rate peaks during the midnight while the rainfall rate peaks in the late evening to early morning in most coastal regions offshore the distribution of the diurnal amplitude shows two maxima one over the mountains and the other in the coastal regions offshore convective rainfall rate peaks in the late afternoon while stratiform rainfall rate peaks in the midnight to early morning the latter dominates the large diurnal amplitude over the mountain areas in the early morning the above broad features are simulated reasonably well in a control experiment with a high resolution regional atmospheric model a sensitivity experiment with the terrain removed is conducted to elucidate the role of orographic forcing in the diurnal evolution of both the local circulation and rainfall patterns the results show that the orographic forcing affects the diurnal precipitation through three major processes first the orography increases the moisture convergence at low levels by blocking and deflecting the mean flow second the upslope winds help initiate convection in the afternoon at the mountaintop finally the deep convection over the mountain acts as a source of propagating gravity waves which help initiate rainbands in the coastal regions offshore in the late evening to early morning implication of the results is discussed

mesoscale variation in diabatic heating around sumatra and its modulation with the madden julian oscillation abstractdiabatic heating in the maritime continent region is controlled by a unique blend of mesoscale variability associated with steep topography and complex coastlines and intraseasonal variabil

the 1993 superstorm cold surge frontal structure gap flow and tropical impact in the wake of the eastern united states cyclone of 12 14 march 1993 a cold surge originating over alaska and western canada brought northerlies exceeding 20 m s21 and temperature decreases up to 158c over 24 h into mexico and central america this paper addresses the multiscale aspects of the surge from the planetary scale to the mesoscale focusing on 1 the structure and evolution of the leading edge of the cold surge 2 the reasons for its extraordinary intensity and equatorward extent and 3 the impact of the surge on the tropics specifically on the strength of the trade winds and on the sea surface temperature in the eastern pacific the cold surge was initiated as a developing cyclone over the gulf of mexico and an upstream anticyclone east of the rockies caused an along barrier pressure gradient to form forcing topographically channeled northerlies along the rocky and sierra madre mountains to transport cold air equatorward on the mesoscale the leading edge of the cold surge possessed nonclassical frontal structure for example as the cold surge entered mexico the coldest air and the strongest wind arrived at about 900 hpa before affecting the surface suggestive of a tipped forward leading edge to the surge also satellite imagery and surface observations indicate that the leading edge appeared to be successively regenerated in the warm presurge air the cold surge had characteristics reminiscent of a kelvin wave a tipped forward cold front a pressure jump line a bore and a gravity current but none of these conceptual dynamical models was fully applicable associated with the cold surge gap winds up to 25 m s21 were observed in the gulfs of tehuantepec a tehuantepecer fonseca papagayo and panama owing to the strong cross mountain pressure gradient in the case of the tehuantepecer a rope cloud emanated from the isthmus of tehuantepec and turned anticyclonically consistent with an inertial oscillation on the synoptic and planetary scales the extraordinary equatorward extent of the cold surge was aided by topographic channeling similar to cold air damming by a low latitude upper tropospheric trough and by the lower branch of the secondary circulation associated with a confluent jet entrance region aloft the cold surge also impacted the tropical atmosphere and ocean by contributing to the strengthening of the northeast trade winds over the eastern pacific ocean and by inducing local cooling of the sea surface temperature in the gulfs of tehuantepec and papagayo by about 48 88c