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The Dynamical-Statistical-Analog Ensemble Forecast model for landfalling tropical cyclones (TCs) precipitation (DSAEF_LTP) utilises an operational numerical weather prediction (NWP) model for the forecast track, while the precipitation forecast is obtained by finding analog cyclones, and making a precipitation forecast from an ensemble of the analogs. This study addresses TCs that occurred from 2004 to 2019 in Southeast China with 47 TCs as training samples and 18 TCs for independent forecast experiments. Experiments use four model versions. The control experiment DSAEF_LTP_1 includes three factors including TC track, landfall season, and TC intensity to determine analogs. Versions DSAEF_LTP_2, DSAEF_LTP_3, and DSAEF_LTP_4 respectively integrate improved similarity region, improved ensemble method, and improvements in both parameters. Results show that the DSAEF_LTP model with new values of similarity region and ensemble method (DSAEF_LTP_4) performs best in the simulation experiment, while the DSAEF_LTP model with new values only of ensemble method (DSAEF_LTP_3) performs best in the forecast experiment. The reason for the difference between simulation (training sample) and forecast (independent sample) may be that the proportion of TC with typical tracks (southeast to northwest movement or landfall over Southeast China) has changed significantly between samples. Forecast performance is compared with that of three global dynamical models (ECMWF, GRAPES, and GFS) and a regional dynamical model (SMS-WARMS). The DSAEF_LTP model performs better than the dynamical models and tends to produce more false alarms in accumulated forecast precipitation above 250 mm and 100 mm. Compared with TCs without heavy precipitation or typical tracks, TCs with these characteristics are better forecasted by the DSAEF_LTP model. [ABSTRACT FROM AUTHOR]

A hypothesis is proposed that the seasonal evolution of sea surface temperature (SST) is the major forcing to control both the onset and the life cycle of the monsoon. A sensitive coupling of surface heat flux and cumulus convection is the central process and, in the current model, is realized by wind-induced surface-heat exchange. The model adopted is a shallow water analog in dynamics with two vertical levels for thermodynamics. The land forcing effect is neglected as a crucial simplification of the model experiments, along with the absence of the dynamical feedback to the SST in the model. Experiments with steady SST forcing reveal the presence of three regimes of response. Weak SST forcing realizes two unsteady regimes, depending on the latitude of the forcing: (i) the supercluster regime, characterized by equatorially trapped eastward propagating convective coherencies akin to the Madden-Julian waves, and (ii) the monsoon regime, characterized by an intermittent planetary-scale standing convective oscillation at the subtropics. For a large SST forcing, a steady response is found similar to the earlier solutions of Matsuno, Webster, and Gill. Experiments with a seasonally varying SST anomaly simulate both the sudden onset and the active-break cycle of the monsoon. In particular the onset is interpreted as the atmosphere undergoing a sudden switch from one dynamical regime to the other. The two unsteady regimes are seen to be in competition, as in the model they cannot coexist. Implications for the atmospheric monsoon are (i) that the SST forcing away from the equator should precede monsoon onset and (ii) that equatorial intraseasonal convective activity should be less active at the time of year when monsoon activity occurs away from the equator.

Empirical orthogonal function (EOF) analyses are performed of time-height series of zonal and meridional winds and of cumulonimbus heating and drying in the Tropics. The data are from a rawinsonde array in the western Pacific located between the equator and 10 [degrees] S during the intensive observation period of the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE). The EOF analyses are performed by applying a window of 20 days to the data and thus calculating the EOFs of the time development of the vertical structure. The wind time series is found to be well represented by two pairs of EOFs, each representing an oscillation. The first oscillation has a period of approximately 40 days, is predominantly in the zonal wind component, and has a first internal mode vertical structure with westerly anomalies in the lower troposphere corresponding to easterly perturbations in the upper troposphere. This pair describes 48.3% of the variance. A second EOF pair in the wind is a zonal variation that occurs predominantly in the upper troposphere. It has a period of approximately 24 days and describes 13.9% of the variance. The heating-drying series is described by a dominant oscillation of period 40 days representing 41% of the variance. The structure is maximum in the middle troposphere and is associated with the same physical phenomenon as the dominant (u, v) oscillation. The second EOF pair for heating-drying has a period of 13 days, so there is a large time separation in periodiocities for heating-drying compared to that for winds. The second (13 day) oscillation in heating-drying has the same vertical structure as the dominant (40 day) oscillation.

During the 120 days of the TOGA COARE intensive observation period, there was an enhanced network of rawinsonde stations covering a large portion of the equatorial West Pacific. These soundings were of sufficient quality and frequency to permit computation of line integral heat and moisture budgets over a variety of large-scale arrays. In this study an enhanced operational dataset is used to compute rainfall, surface heat, and moisture fluxes, and vertical profiles of diabatic and/or subgrid-scale heating and moistening over these arrays. Time series of daily rainfall computed from heat and moisture budgets are presented over seven arrays, including the intensive flux array, outer sounding array, and large-scale array. Vertical profiles of apparent heat source and apparent moisture sink are analyzed and presented for different arrays and for different rainfall rates. The mean budget-derived rainfall ranged from 4 to 12 mm [day.sup.-1] over the various arrays, with the most rain occurring within the intensive flux array and the least over Papua New Guinea. Correlations between convective indicators, low-level winds, and surface fluxes indicate that convection tends to precede or be coincident with increased surface fluxes in the more active regions south of the equator but not in the less convectively active regions. Convective heating in this region tends to be vertically distributed in a dominant single mode, apparently a characteristic blend of convective and stratiform rain heating, with a broad peak in the midtroposphere around 400-500 mb. This distribution varies surprisingly little from day to day or with rainfall intensity. In contrast, convection over Papua New Guinea differs from the maritime convection. The convection over this large island produces more heating at upper-tropospheric levels than does the surrounding maritime convection. This indicates a fundamental difference between maritime and island rainfall that may well have significant effects on global-scale circulations.

Linear convective instability is revisited to demonstrate the structurally different growth rates of disturbances in balanced and unbalanced models where diabatic heating is parameterized to be proportional to the vertical mass flux, and Ekman-type lower boundary conditions are introduced. The heating parameterization leads to an 'effective static stability,' which is negative when the vertical cumulus mass flux exceeds the total mass flux. This results in large-scale convective overturning. The appropriate horizontal scale is the usual Rossby deformation radius modified by the parameter [square root of [Gamma] - 1], where [Gamma] is the ratio of cumulus to total mass flux. The unbalanced flow instability varies from zero growth ([Sigma] = 0) at finite horizontal scale (corresponding to twice the modified deformation radius L = 2R) to infinitely large values ([Sigma] [approaches] [infinity]) at smallest scales (L [right arrow] 0). The growth of the related balanced model commences at the same scale (L = 2R) but attains infinitely large values on approaching the scale of the modified deformation radius L = R. This short-wave cutoff appears as a result of the changing vertical mass flux-heating profile associated with the Ekman boundary condition. Growth rates, horizontal length scales, and associated mass flux profiles are qualitatively supported by observations. A feature of the solution is its dependence on vertical structure. Specifically, for each imposed vertical structure there are two solutions: one unbalanced corresponding to the cloud scale, and one balanced corresponding to the scale of the modified deformation radius. It is the thesis of this paper that the latter (large scale) solution represents a viable mechanism for the initial growth of either cloud clusters or tropical cyclones in nature.

Seventeen years of 3‐hr, 0.25° resolution, precipitation data from the Tropical Rainfall Measurement Mission (TRMM) multi‐satellite precipitation analysis (TMPA) product are used to develop a global climatology of precipitation in tropical cyclones (TCs). Due to very large SDs for rainfall in each stratification by intensity class or cyclone basin, our methodology concentrates on frequency distributions and percentage representation in different rainfall rate categories. The stratifications reveal that the TC rainfall climatologies are dependent on three inter‐related factors: TC intensity, TC size and TC basin. The interdependence of the three is examined. The distributions of TC intensity classes in the different basins are not a significant contributor to the fact that certain basins (Northwest Pacific, North Atlantic) have higher TC rainfall rates than other basins (Northeast Pacific, South Indian). In contrast to this, the distributions of TC size classes between basins are a significant contributor to why some basins are wetter than others. A climatology is also presented of lifetime accumulated rainfall (LAR) in TCs. The record LAR belongs to hurricane Ivan in 2004, with 300 km3 of rain over the 0–350 km radius, and 432 km3 over 0–500 km. The largest LAR values occur almost exclusively in two cyclone basins: The Northwest Pacific and the North Atlantic. Not unexpectedly, LAR is determined primarily by TC duration, which accounts for around 70% of the variance. Examination of the full 17‐year dataset reveals a decreasing trend in both median and extreme TC rainfall rates in all basins except the Northeast Pacific. However, mechanisms responsible for this decrease are yet to be identified and may be primarily due to the sample size or data inhomogeneities. The difference between the trends and those expected from physical principles is a concern which we hope will be taken up by other investigators. [ABSTRACT FROM AUTHOR]

Recent research has strengthened the understanding of the links between climate and tropical cyclones (TCs) on various timescales. Geological records of past climates have shown century-long variations in TC numbers. While no significant trends have been identified in the Atlantic since the late 19th century, significant observed trends in TC numbers and intensities have occurred in this basin over the past few decades, and trends in other basins are increasingly being identified. However, understanding of the causes of these trends is incomplete, and confidence in these trends continues to be hampered by a lack of consistent observations in some basins. A theoretical basis for maximum TC intensity appears now to be well established, but a climate theory of TC formation remains elusive. Climate models mostly continue to predict future decreases in global TC numbers, projected increases in the intensities of the strongest storms and increased rainfall rates. Sea level rise will likely contribute toward increased storm surge risk. Against the background of global climate change and sea level rise, it is important to carry out quantitative assessments on the potential risk of TC-induced storm surge and flooding to densely populated cities and river deltas. Several climate models are now able to generate a good distribution of both TC numbers and intensities in the current climate. Inconsistent TC projection results emerge from modeling studies due to different downscaling methodologies and warming scenarios, inconsistencies in projected changes of large-scale conditions, and differences in model physics and tracking algorithms. WIREs Clim Change 2016, 7:65-89. doi: 10.1002/wcc.371 For further resources related to this article, please visit the . [ABSTRACT FROM AUTHOR]

The impact of global ENSO on the regional monsoon onset over the Maritime Continent is examined, using satellite-derived scatterometer surface winds over the sea channel from the South China Sea, through the Karimata Strait into the Java Sea. An index of monsoon onset, fracsign, is defined based on a positive dot-product between the monthly wind at each gridpoint and the "basis-wind" or climatological wind at the peak of the relevant monsoon season. Rather than being delayed throughout the Maritime Continent during El Niño years, the monsoon is seen to arrive faster at and remain longer over the western Maritime Continent, and therefore delayed for the eastern Maritime Continent. The wind-based diagnostic can be further decomposed into two components that reflect the monsoon wind strength and the location of the wind convergence zone, respectively. During El Niño years, the monsoon strength post-onset is weaker than normal over the eastern maritime continent. However, there is no ENSO-related differentiation in monsoon strength post-onset over the western Maritime Continent. [ABSTRACT FROM AUTHOR]