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A case study of an intraseasonal oscillation (ISO) is investigated in the period leading up to its conectively active phase during the Mirai Indian Ocean Cruise for the Study of the MJO-Conveetion Onset (MISMO), which was conducted during boreal autumn 2006. Detailed observations, including apparent heat and moisture analyses, reveal that synoptic-scale variability of heat and moisture sources and sinks associated with the passage of three eastward-propagating cloud systems (EPCSs) was prominent during this period. These systems with periods of ~6 days propagated through the MISMO domain, priming the atmosphere for a convectively active phase of the ISO. The prominent shallow heating during this period may explain the rather slow (8 m [s.sup.-1]) propagation speed for EPCSs. The zonal structure and sign of the frictional convergence show that these EPCSs have common characteristics to the frictional Kelvin mode studied by Ohuchi and Yamasaki. With the analyses of the period-averaged vertical profiles, the EPCSs were identified as the principal mechanism to moisten the atmosphere prior to the ISO convectively active phase. DOI: 10.1175/2009JAS3003.1

Heating profiles calculated from sounding networks and other observations during three Tropical Rainfall Measuring Mission (TRMM) field campaigns [the Kwajalein Experiment (KWAJEX), TRMM Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA), and South China Sea Monsoon Experiment (SCSMEX)] show distinct geographical differences between oceanic, continental, and monsoon regimes. Differing cloud types (both precipitating and nonprecipitating) play an important role in determining the total diabatic heating profile. Variations in the vertical structure of the apparent heat source, [Q.sub.1], can be related to the diurnal cycle, large-scale forcings such as atmospheric waves, and rain thresholds at each location. For example, TRMM-LBA, which occurred in the Brazilian Amazon, had mostly deep convection during the day while KWAJEX, which occurred in the western portion of the Pacific intertropical convergence zone, had more shallow and moderately deep daytime convection. Therefore, the afternoon height of maximum heating was more bottom heavy (i.e., heating below 600 hPa) during KWAJEX compared to TRMM-LBA. More organized convective systems with extensive stratiform rain areas and upper-level cloud decks tended to occur in the early and late morning hours during TRMM-LBA and KWAJEX, respectively, thereby causing [Q.sub.1] profiles to be top heavy (i.e., maxima from 600 to 400 hPa) at those times. SCSMEX, which occurred in the South China Sea during the monsoon season, had top-heavy daytime and nighttime heating profiles suggesting that mesoscale convective systems occurred throughout the diurnal cycle, although more precipitation and upper-level cloud in the afternoon caused the daytime heating maximum to be larger. A tendency toward bottom- and top-heavy heating profile variations is also associated with the different cloud types that occurred before and after the passage of easterly wave troughs during KWAJEX, the easterly and westerly regimes during TRMM-LBA, and the monsoon onset and postonset active periods during SCSMEX. Rain thresholds based on heavy, moderate, and light/no-rain amounts can further differentiate top-heavy heating, bottom-heavy heating, and tropospheric cooling. These budget studies suggest that model calculations and satellite retrievals of [Q.sub.1] must account for a large number of factors in order to accurately determine the vertical structure of diabatic heating associated with tropical cloud systems.

Rawinsonde data used for sounding-array budget computations have random errors, both instrumental errors and errors of representativeness (here called sampling errors). The latter are associated with the fact that radiosondes do not measure large-scale mean winds and state variables, but are contaminated by small-scale variations as well. Data from the western Pacific and the summer monsoon of southeast Asia are used to estimate these random errors, and to propagate them through budget computations to assign error bars to derived quantities. The statistics of sampling errors in directly measured variables are estimated from station pair analysis, in which variance is partitioned into contributions by resolved and unresolved scales. Resolved scales contribute the portion that is contained in averages of adjacent sounding stations and/or adjacent launch times (6-h intervals), while the rest of the total variance is defined as unresolved. Magnitudes of unresolved variability for typical rawinsonde-array spacings are ~0.5 K for temperature; ~5% for relative humidity at low levels, rising to nearly 15% in the middle-upper troposphere; and ~2 m [s.sup.-1] for winds, rising to 3 m [s.sup.-1] in the upper troposphere. These are much larger than random instrumental errors, as estimated from pairs of simultaneous rawinsondes launched very close together. Vertical correlation scales of unresolved variability are 100-200 hPa. Up to 50% of the variance of humidity is unresolved, while for zonal wind the unresolved portion is only a few percent. Spatial and temporal sampling errors become about equal for 6-hourly rawinsondes ~200 km apart. The effects of sampling errors on budget computations are estimated by a perturbed-observation ensemble approach. All computations are repeated 20 times, with random realizations of unresolved variability added to the rawinsonde data entering the analysis. The ensemble standard deviation serves as an estimate of sampling error, which naturally decreases as the results are averaged over larger areas and longer time periods. For example, rainfall estimates on ~500 km scales have sampling errors of ~5 mm [day.sup.-1] in daily means, and ~1 mm [day.sup.-1] in monthly means. The ensemble spread of 120-day time integrations of the vertically averaged moist enthalpy equation with rawinsonde-array-derived advective sources exceeds 20 K, implying that sampling error could be responsible for substantial biases in column models forced with such source terms.

Rawinsonde data collected from the Atlantic Stratocumulus Transition Experiment (ASTEX) were used to investigate the mean and temporal characteristics of large-scale heat and moisture budgets for a 2-week period in June 1992. During this period a large apparent heat sink and an apparent moisture source were observed near inversion base. Analyses from other budget studies show that similar convective signatures occur in a wide variety of regimes when trade wind-type inversions are present. In the lowest kilometer the vertical eddy flux of moist static energy over the ASTEX domain (centered at 33 degrees N with an average sea surface temperature of 19.4 degrees C) is about 60% of that observed in the undisturbed trade wind regime of BOMEX (centered at 15 degrees N with an average sea surface temperature of 28.1 degree C). The apparent heat source, apparent moisture sink, and convective flux of moist static energy over ASTEX were strongly modulated on a synoptic timescale by the passage of fronts and by fluctuations in the subsidence rate associated with changes in the strength and position of the subtropical high. The influence of midlatitude disturbances on convection over ASTEX further distinguishes this region from the trade wind and tropical regimes. Daily budgets are examined for three different convective regimes during ASTEX to determine the mechanisms contributing to the large synoptic variability over this region.

Seven lithologic formations, ranging in age from Oligocene to Pleistocene, were recently penetrated by core holes in southernmost Florida. From bottom to top, they are the early Oligocene Suwannee Limestone; late-early Oligocene-to-Miocene Arcadia Formation, basal Hawthorn Group; late Miocene Peace River Formation, upper Hawthorn Group; newly proposed late Miocene-to-Pliocene Long Key and Stock Island Formations; and Pleistocene Key Largo and Miami Limestones. The rocks of the Suwannee Limestone form a third-order sequence. Although the entire thickness was not penetrated, 96 m of Suwannee core from one well contains at least 50 vertically stacked, exposure-capped limestone cycles, presumably related to rapid eustatic fluctuations while experiencing tropical to subtropical conditions. The Arcadia Formation is a composite sequence containing four high frequency sequences composed of multiple vertically stacked carbonate cycles. Most cycles do not show evidence of subaerial exposure and were deposited under more temperate conditions, relative to the Suwannee Limestone. The Arcadia Formation in southernmost Florida is bounded by regional unconformities representing third-order sequence boundaries. Post-Arcadia transgression produced a major backstepping of sediment accumulation above the upper sequence boundary of the Arcadia Formation. The Peace River Formation, composed of diatomaceous mudstones, has been identified only beneath the Florida peninsula and is not present beneath the Florida Keys. Deposition occurred during marine transgressive to high-stand conditions and a local phosphatization event (recorded in northeast Florida). The transgression is possibly related to a global rise in sea level, which resulted in upwelling of relatively cooler, relatively nutrient-rich water masses onto the Florida Platform. It is proposed that the absence of Peace River sediments beneath the Keys is due to sediment bypass of the upper surface of the Arcadia, a result of sediment sweeping by an ancestral Florida current. During late Miocene to Pliocene time in the Florida Keys, siliciclastics of the Long Key Formation and fine-grained carbonates of the Stock Island Formation prograded toward the southern edge of the Florida Platform and downlapped onto the regional unconformity at the top of the Arcadia. Shallow-marine Pleistocene limestones (Key Largo and Miami Limestones), deposited during tropical to subtropical conditions, drape over accretionary successions of the Long Key and Stock Island Formations.

The Eliassen transverse circulation equation is derived from the set of f-plane, semigeostrophic, slab-symmetric equations with the inclusion of both diabatic heating and ambient shear effects. Numerical integrations of this model in geostrophic coordinates are performed in the context of a typical midlatitude squall line characterized by a leading convective line and a trailing stratiform rain region. Some dynamical insights are provided by these integrations in conjunction with the theoretical framework, which seem to be unavailable by primitive-equation model simulations. A more complete dynamical picture of a squall line circulation system is revealed from this study: a balanced midlevel horizontal vortex coupled with an ageostrophic transverse circulation in the normal-line plane. This configuration suggests an interaction between two distinct dynamical scales, that is, the scales with geostrophic and ageostrophic-like motions, both of which play important roles in mesoscale convective systems. The internal and external physical processes that affect the ageostrophic transverse circulation are further discussed.

Soundings taken from the tropical western Pacific warm pool region during TOGA COARE reveal the common occurrence of temperature and moisture perturbations near the 0 [degrees] C level. The perturbations frequently are characterized by shallow layers of increased stability (or occasionally temperature inversions) and reversals or inflections in the vertical profile of specific humidity. Similar temperature and moisture inversions have been observed elsewhere in the Tropics and midlatitudes but have not received much attention. Isothermal layers are known to exist just below the melting level in stratiform rain regions; however, not all stable layers observed over the warm pool are confined to precipitation systems. The perturbation in the specific humidity profile accounts for the often-observed double-peak structure in the apparent moisture sink [Q.sub.2] in the Tropics. Stratification of the data based on relative humidity criteria indicates that the stable layers near the 0 [degrees] C level generally fall into two main classifications: anomalously cool - moist conditions at and slightly below the 0 [degrees] C level and anomalously warm - dry conditions at and just above. The former occur primarily within or in close proximity to precipitating systems, suggesting they are a result of the direct effects of melting. Soundings in the latter group typically occur outside convective areas. Mechanisms for formation of the warm - dry stable layers are unclear at this time, but advective, radiative, gravity wave, and melting effects may all play some role. In some cases they may simply be remnant melting layers from past convection. There is evidence to indicate that the stable layers near the 0 [degrees] C level affect tropical cloud populations. Convection impinging upon or penetrating the stable layers may detrain significantly near the 0 [degrees] C level, thereby contributing to perturbations in the moisture profile there. Midlevel cloud layers that are commonly observed in the Tropics may be evidence of this detrainment. Another primary finding is the frequent occurrence of a trade wind stable layer over the warm pool. Though not widely recognized, this finding is consistent with the prevalence of trade cumulus clouds in the western Pacific region. The trade inversions often coexist with, but are distinct from, the inversions near the 0 [degrees] C level.

Analyses of atmospheric heat and moisture budgets serve as an effective tool to study convective characteristics over a region and to provide large‐scale forcing fields for various modeling applications. This paper examines two popular methods for computing large‐scale atmospheric budgets: the conventional budget method (CBM) using objectively gridded analyses based primarily on radiosonde data and the constrained variational analysis (CVA) approach which supplements vertical profiles of atmospheric fields with measurements at the top of the atmosphere and at the surface to conserve mass, water, energy, and momentum. Successful budget computations are dependent on accurate sampling and analyses of the thermodynamic state of the atmosphere and the divergence field associated with convection and the large‐scale circulation that influences it. Utilizing analyses generated from data taken during Dynamics of the Madden‐Julian Oscillation (DYNAMO) field campaign conducted over the central Indian Ocean from October to December 2011, we evaluate the merits of these budget approaches and examine their limitations. While many of the shortcomings of the CBM, in particular effects of sampling errors in sounding data, are effectively minimized with CVA, accurate large‐scale diagnostics in CVA are dependent on reliable background fields and rainfall constraints. For the DYNAMO analyses examined, the operational model fields used as the CVA background state provided wind fields that accurately resolved the vertical structure of convection in the vicinity of Gan Island. However, biases in the model thermodynamic fields were somewhat amplified in CVA resulting in a convective environment much weaker than observed. Plain Language Summary: Two popular methods for computing large‐scale atmospheric budgets are examined: the conventional budget method (CBM) using primarily sounding data (i.e., vertical profiles describing the state of the atmosphere) and the constrained variational analysis (CVA) approach which supplements sounding data with measurements at the top of the atmosphere and at the surface to conserve mass, water, energy, and momentum. Successful budget computations are dependent on accurate sampling and analyses of the thermodynamic state of the atmosphere and the wind field associated with convection and the large‐scale circulation that influences it. Utilizing analyses generated from data taken during Dynamics of the Madden‐Julian Oscillation (DYNAMO) field campaign conducted over the central Indian Ocean, we evaluate the merits of these budget approaches and examine their limitations. While many of the shortcomings of the CBM are effectively minimized with CVA, the success of the CVA approach is dependent on reliable background fields and rainfall constraints. Merits and limitations of both methods are summarized. Key Points: Merits and limitations of two methods for computing large‐scale atmospheric budgets are examinedConstrained variational analysis (CVA) method effectively minimizes many of the shortcomings of the conventional budget methodHowever, accurate large‐scale diagnostics in CVA are dependent on reliable background fields and rainfall constraints [ABSTRACT FROM AUTHOR]

In schematic north-south cross sections the trade inversion layer is often depicted as sloping upward as air flows toward the intertropical convergence zone. This conceptual view is consistent with purely thermodynamic boundary-layer models, which predict a deeper boundary layer with increasing sea surface temperature and decreasing large-scale subsidence. The slopes implied by such thermodynamic models and incorporated into schematic diagrams are approximately 2000 m/1000 km. In contrast, observational studies of the inversion structure over the Atlantic and Pacific Oceans reveal a less dramatic slope, on the order of 300 m/1000 km. To address this inconsistency, the authors adopt a somewhat different view of the trade inversion layer. In particular, rather than regarding it as a purely thermodynamic structure, it is regarded as a dynamical structure. By formulating a generalization of the Rossby adjustment problem, the authors investigate the dynamical adjustments of a trade wind inversion layer of variable strength and depth. From the solution of the adjustment problem, there emerges the notion that the subtropics control the inversion structure in the Tropics; that is, the subtropical inversion height is dynamically extended into the Tropics in such a way that there is little variation in the depth of the boundary layer.

Properties of the atmospheric boundary layer (ABL) over the central Indian Ocean are investigated using sounding data obtained during the Dynamics of the MJO (DYNAMO) field campaign in 2011/12. Observations from Gan Island on Addu Atoll, the R/V Revelle, and Malé in the Maldives are used to determine the frequency of well-mixed layers and their mean thermodynamic and wind profiles. Well-mixed boundary layers or mixed layers were observed 68% of the time from the three sites, ranging from ~100-m depth in recovering convective downdraft wakes to ~925 m in undisturbed conditions, with a mean depth of 508 m. At Revelle, the site most representative of the open ocean, the ABL displayed a distinct signal of modulation by the October and November MJOs, with mixed-layer depths gradually increasing through the suppressed phases as the sea surface temperature (SST) increased leading up to the active phases, followed by frequent ABL stabilization and shallow mixed layers in recovering wakes. A distinct diurnal cycle of mixed-layer depths and properties was observed during the MJO suppressed phases in response to a diurnal cycle of the SST under the mostly light-wind, clear-sky conditions. The daytime growth of the mixed layer contributed to an afternoon maximum in cumulus cloud development and rainfall during the suppressed periods by allowing more boundary layer thermals to reach their condensation levels. The variability of the ABL on time scales ranging from convective to diurnal to monthly poses significant challenges for numerical simulations of the MJO and the tropical circulation in general. [ABSTRACT FROM AUTHOR]

Sounding data from Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) have provided a first opportunity to document the variability of the atmospheric mixed layer over the western Pacific warm pool on timescales ranging from diurnal to intraseasonal. Six-hourly sounding data from four sites--the atoll Kapingamarangi and R/Vs Moana Wave, Shiyan 3, and Xiangyanghong 5--are used to determine the mixed layer depth and its thermodynamic properties. Almost three-quarters of the soundings at these four sites exhibited well-mixed structures: nearly constant profiles of potential temperature and specific humidity capped by a ~150-m-deep entrainment zone. The majority of the remaining soundings were modified by precipitation and their associated downdrafts. It is estimated that approximately 40%-50% of the total soundings in COARE were influenced by precipitation downdrafts. The mean mixed layer depth at the four sites was 512 m with large variations on multiple timescales. Mean depths decreased across the warm pool from west to east, consistent with the west-to-east increase in precipitation averaged over the 4-month Intensive Observing Period. Significant modulation of the mixed layer occurred on the timescale of the Madden-Julian oscillation (MJO): the mean depth was 562 m during the undisturbed, light-wind period prior to the strong westerly wind burst (WWB) associated with the December MJO; it decreased to 466 m during the heavy-rain period of the WWB, reflecting numerous, recovering precipitation downdraft wakes; and then increased to 629 m during the late stages of the WWB when precipitation had ended. Dry intrusions over the warm pool caused the mixed layer to deepen at times to 800 m and more. Since the surface buoyancy flux typically did not increase at these times, the deepening is linked to a suppression of shallow cumulus clouds by the dry air (reduced between-cloud subsidence) as well as a general reduction in the overall shower activity and associated precipitation downdrafts. Dry intrusions also acted to enhance radiative cooling in the mixed layer. A diurnal cycle in the mixed layer depth was observed, with maximum amplitude in undisturbed (mostly clear), light-wind conditions. The mixed layer was deepest and warmest in the afternoon in direct response to 1) an afternoon peak in the surface buoyancy flux, which, in turn, arose from the large diurnal cycle in SST (up to 2 [degrees] -3 [degrees] C) on light-wind days, and 2) absorption of solar shortwave radiation. Thus, the atmospheric mixed layer over the warm pool during undisturbed conditions behaves like that over land, albeit with a weaker diurnal cycle amplitude, but sufficient to generate an afternoon maximum in shallow cumulus clouds and precipitation. This pattern is distinct from the typical early morning maximum in rainfall during disturbed conditions over tropical oceans. Diagnosis of the mixed layer net radiative cooling rate during light-wind conditions indicates a large diurnal range, from ~-1.5 K [day.sup.-1] at midday to nearly -3 K [day.sup.-1] at night.

The diurnal cycle of the marine boundary layer over the Atlantic Stratocumulus Transition Experiment (ASTEX) domain is examined during a two-week period of June 1992 in several fields, including: fractional low cloudiness, various parameters that enter into the heat and moisture budgets (e.g., temperature, water vapor mixing ratio, vertical motion), the budgets themselves, radiative heating, and the vertical eddy flux of moist static energy. Results show fractional low cloudiness varies over this region from a maximum of 54% in the predawn hours to a minimum of 39% in the midafternoon. These changes in low cloudiness are accompanied by an opposite trend in the boundary layer moisture, which shows a predawn drying and an afternoon moistening. Large-scale vertical motion also varies diurnally with a peak amplitude of 0.12 cm [s.sup.-1] at 1.8 km, which is a ~20% variation from the mean subsidence rate. Cloud-radiative processes play an important role in determining the diurnal characteristics of the vertical eddy flux of moist static energy, with a peak amplitude in the cloud layer at 1.2 km and a variation at this level from 24 W [m.sup.-2] at 1300 LST to 100 W [m.sup.-2] at 0400 LST. These diurnal changes suggest that the early morning peak in eddy flux results in a drying of the subcloud layer as moisture transport into the cloud layer is enhanced, leading to the observed low-cloud maximum. In contrast, during the daylight hours, solar heating within the cloud leads to a well-mixed cloud layer, a stabilizing of the subcloud layer with respect to the cloud layer, a decoupling of the cloud and subcloud layers, and ultimately, a thinning or reduction of the low clouds. Comparison of the diurnal cycle of summertime low-level divergence and vertical motion from this study with earlier published results from other regions in the North Atlantic shows a complex diurnal pattern with alternating phase in adjacent latitude belts across this region. The sense of these phase changes suggests that the northern branch of the Hadley circulation from roughly 5 [degrees] N to 25 [degrees] N over the eastern Atlantic is pulsing diurnally with enhanced mass flow during the early morning hours.

Atmospheric heat and moisture budgets are used to determine rainfall and radiative heating rates over the western Pacific warm pool during the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE). Results are compared to independent estimates of these quantities from the other sources. Using the COARE bulk flux algorithm to estimate surface evaporation over the intensive flux array (IFA), the IFA moisture budget-derived average rainfall for the 120-day intensive observing period (IOP) is 8.2 mm [day.sup.-1]. This value agrees closely with recent estimates from satellites and the ocean salinity budget. For a smaller area within the IFA containing the rain-mapping domain of the TOGA and Massachusetts Institute of Technology 5-cm radars, the atmospheric budget for the 101-day radar deployment yields 6.8 mm [day.sup.-1], slightly greater than the independent radar rain rate estimate of 5.4 mm [day.sup.-1]. Comparison of budget-derived rainfall with National Centers for Environmental Prediction and European Centre for Medium-Range Weather Forecasts reanalyses indicates that the reanalyses produce excessive precipitation in the northern ITCZ (around 10 [degrees] N) in association with anomalously moist low-level conditions at those latitudes. These anomalous conditions arise from moist-biased VIZ humidity sensors on rawinsondes launched at operational sites there, while outside those latitudes dry-biased Vaisala sensors were almost exclusively used. Computation of the vertically integrated net radiative heating rate as a residual from the heat and moisture budgets reveals a ~1.5 K [day.sup.-1] variation on the timescale of the Madden-Julian oscillation. The implied horizontal variation of is large enough to have significant impacts on the tropical Walker and Hadley circulations. The IFA-IOP mean is -0.41 K [day.sup.-1]. This net cooling rate is less than many previous estimates for the Tropics but is within the range of independent estimates for COARE based on radiation models and observations. This small value may arise from decreased longwave emission to space due to abundant cirrus over the warm pool and, in addition, may reflect some shortwave absorption by cirrus, but not necessarily 'anomalous absorption' as has been recently proposed.

This study examines the westward-propagating convective disturbances with quasi-2-day intervals of occurrence identified over Gan Island in the central Indian Ocean from mid- to late October 2011 during the Dynamics of the Madden-Julian Oscillation (DYNAMO) field campaign. Atmospheric sounding, satellite, and radar data are used to develop a composite of seven such disturbances. Composites and spectral analyses reveal that 1) the quasi-2-day convective events comprise westward-propagating diurnal convective disturbances with phase speeds of 10-12ms-1 whose amplitudes are modulated on a quasi-2-day time scale on a zonal scale of ~1000 km near the longitudes of Gan; 2) the cloud life cycle of quasi-2-day convective disturbances shows a distinct pattern of tropical cloud population evolution--from shallow to deep to stratiform convection; 3) the time scales of mesoscale convective system development and boundary layer modulation play essential roles in determining the periodicity of the quasi-2-day convective events; and 4) in some of the quasi-2-day events there is evidence of counterpropagating (westward and eastward) cloud systems along the lines proposed by Yamada et al. Based on these findings, an interpretation is proposed for the mechanisms for the quasi-2-day disturbances observed during DYNAMO that combines concepts from prior studies of this phenomenon over the western Pacific and Indian Oceans. [ABSTRACT FROM AUTHOR]