scholarly journals Transition between Suppressed and Active Phases of Intraseasonal Oscillations in the Indo-Pacific Warm Pool

2006 ◽  
Vol 19 (21) ◽  
pp. 5519-5530 ◽  
Author(s):  
P. A. Agudelo ◽  
J. A. Curry ◽  
C. D. Hoyos ◽  
P. J. Webster
Keyword(s):  
Large Scale ◽  
Transition Period ◽  
Numerical Models ◽  
Convective Available Potential Energy ◽  
Lower Troposphere ◽  
Diagnostic Study ◽  
Tropical Ocean ◽  
Toga Coare ◽  
Ocean Atmosphere ◽  
Intraseasonal Oscillations

Abstract Intraseasonal oscillations (ISOs) are important large-amplitude and large-scale elements of the tropical Indo-Pacific climate with time scales in the 20–60-day period range, during which time they modulate higher-frequency tropical weather. Despite their importance, the ISO is poorly simulated and predicted by numerical models. A joint diagnostic and modeling study of the ISO is conducted, concentrating on the period between the suppressed and active (referred to as the “transition”) period that is hypothesized to be the defining stage for the development of the intraseasonal mode and the component that is most poorly simulated. The diagnostic study uses data from the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). It is found that during the transition period, the ocean and the atmosphere undergo gradual but large-scale and high-amplitude changes, especially the moistening of the lower troposphere caused jointly by the anomalously warm sea surface temperature arising from minimal cloud and low winds during the suppressed phase and the large-scale subsidence that inhibits the formation of locally deep convection. Using a cloud classification scheme based on microwave and infrared satellite data, it is observed that midtop (cloud with a top in the middle troposphere) nonprecipitating clouds are a direct response of the low-level moisture buildup. To investigate the sensitivity of ISO simulations to the transitional phase, the European Centre for Medium-Range Weather Forecasts (ECMWF) coupled ocean–atmosphere climate model is used. The ECMWF was run serially in predictive ensemble mode (five members) for 30-day periods starting from 1 December 1992 to 30 January 1993, encompassing the ISO occurring in late December. Predictability of the active convective period of the ISO is poor when initialized before the transitional phases of the ISO. However, when initialized with the correct lower-tropospheric moisture field, predictability increases substantially, although the model convective parameterization appears to trigger convection too quickly without allowing an adequate buildup of convective available potential energy during the transition period.

scholarly journals An Initiation Process of Tropical Depression-type Disturbances under the Influence of Upper-level Troughs

2021 ◽  
Author(s):  
Yuya Hamaguchi ◽  
Yukari N. Takayabu
Keyword(s):  
Large Scale ◽  
Convective Available Potential Energy ◽  
Three Dimensional ◽  
Lower Troposphere ◽  
Dimensional Structure ◽  
Convective Heating ◽  
Upper Troposphere ◽  
Tropical Depression ◽  
Upper Level ◽  
Extratropical Forcing

AbstractIn this study, the statistical relationship between tropical upper-tropospheric troughs (TUTTs) and the initiation of summertime tropical-depression type disturbances (TDDs) over the western and central North Pacific is investigated. By applying a spatiotemporal filter to the 34-year record of brightness temperature and using JRA-55 reanalysis products, TDD-event initiations are detected and classified as trough-related (TR) or non-trough-related (non-TR). The conventional understanding is that TDDs originate primarily in the lower-troposphere; our results refine this view by revealing that approximately 30% of TDDs in the 10°N-20°N latitude ranges are generated under the influence of TUTTs. Lead-lag composite analysis of both TR- and non-TR-TDDs clarifies that TR-TDDs occur under relatively dry and less convergent large-scale conditions in the lower-troposphere. This result suggests that TR-TDDs can form in a relatively unfavorable low-level environment. The three-dimensional structure of the wave activity flux reveals southward and downward propagation of wave energy in the upper troposphere that converges at the mid-troposphere around the region where TR-TDDs occur, suggesting the existence of extratropical forcing. Further, the role of dynamic forcing associated with the TUTT on the TR-TDD-initiation is analyzed using the quasi-geostrophic omega equation. The result reveals that moistening in the mid-to-upper troposphere takes place in association with the sustained dynamical ascent at the southeast side of the TUTT, which precedes the occurrence of deep convective heating. Along with a higher convective available potential energy due to the destabilizing effect of TUTTs, the moistening in the mid-to-upper troposphere also helps to prepare the environment favorable to TDDs initiation.

scholarly journals Sand/dust storm processes in Northeast Asia and associated large-scale circulations

2008 ◽  
Vol 8 (1) ◽  
pp. 25-33 ◽  
Author(s):  
Y. Q. Yang ◽  
Q. Hou ◽  
C. H. Zhou ◽  
H. L. Liu ◽  
Y. Q. Wang ◽  
...  
Keyword(s):  
Dust Storm ◽  
General Circulation ◽  
Large Scale ◽  
Transition Period ◽  
Northeast Asia ◽  
Lower Troposphere ◽  
Northern China ◽  
Wind Anomaly ◽  
Cold Air ◽  
Sand Dust

Abstract. This paper introduces a definition of sand/dust storm process as a new standard and idea of sand/dust storm (SDS) groups a number of SDS-events in Northeast Asia. Based on the meteorological data from WMO/GOS network, 2456 Chinese surface stations and NCEP-NCAR reanalysis, the sand/dust storm processes in Northeast Asia in spring 2000–2006 are investigated. And the evolutions of anomalies of general circulation in the troposphere are analyzed by comparing the spring having most and least occurrences of SDS in year 2006 and 2003. Associated with the noticeably increased occurrence of SDS processes in spring 2006, the anomalies in 3-D structure of general circulation especially in the mid-and high latitudes of the Northen Hemisphere (NH) are revealed. The transition period from the winter of 2005 to spring 2006 has witnessed a fast-developed high center over the circumpolar vortex area in the upper troposphere, which pushes the polar vortex more southwards to mid-latitudes with a more extensive area over the east NH. In spring 2006, there are the significant circulation anomalies in the middle troposphere from the Baikal Lake to northern China with a stronger southward wind anomaly over Northeast Asia. Compared with a normal year, stronger meridional wind with a southward wind anomaly also in the lower troposphere prevail over the arid and semiarid regions in Mongolia and northern China during spring 2006. The positive anomalies of surface high pressure registered an abnormal high of 4–10 hPa in the Tamil Peninsular make a stronger cold air source for the repeated cold air outbreak across the desert areas in spring 2006 resulting in the most frequent SDS seasons in the last 10 years in Northeast Asia.

Corrected TOGA COARE Sounding Humidity Data: Impact on Diagnosed Properties of Convection and Climate over the Warm Pool

2003 ◽  
Vol 16 (14) ◽  
pp. 2370-2384 ◽  
Author(s):  
Paul E. Ciesielski ◽  
Richard H. Johnson ◽  
Patrick T. Haertel ◽  
Junhong Wang
Keyword(s):  
Cloud Model ◽  
Convective Available Potential Energy ◽  
Vertical Motion ◽  
Warm Pool ◽  
Radiative Heating ◽  
Tropical Ocean ◽  
Toga Coare ◽  
Beneficial Impact ◽  
Corrected Data ◽  
The Difference

Abstract This study reports on the humidity corrections in the Tropical Ocean Global Atmosphere (TOGA) Coupled Ocean–Atmosphere Response Experiment (COARE) upper-air sounding dataset and their impact on diagnosed properties of convection and climate over the warm pool. During COARE, sounding data were collected from 29 sites with Vaisala-manufactured systems and 13 sites with VIZ-manufactured systems. A recent publication has documented the characteristics of the humidity errors at the Vaisala sites and a procedure to correct them. This study extends that work by describing the nature of the VIZ humidity errors and their correction scheme. The corrections, which are largest in lower-tropospheric levels, generally increase the moisture in the Vaisala sondes and decrease it in the VIZ sondes. Use of the corrected humidity data gives a much different perspective on the characteristics of convection during COARE. For example, application of a simple cloud model shows that the peak in convective mass flux shifts from about 8°N with the uncorrected data to just south of the equator with corrected data, which agrees better with the diagnosed vertical motion and observed rainfall. Also, with uncorrected data the difference in mean convective available potential energy (CAPE) between Vaisala and VIZ sites is over 700 J kg−1; with the correction, both CAPEs are around ∼1300 J kg−1, which is consistent with a generally uniform warm pool SST field. These results suggest that the intensity and location of convection would differ significantly in model simulations with humidity-corrected data, and that the difficulties which the reanalysis products had in reproducing the observed rainfall during COARE may be due to the sonde humidity biases. The humidity-corrected data appear to have a beneficial impact on budget-derived estimates of rainfall and radiative heating rate, such that revised estimates show better agreement with those from independent sources.

scholarly journals Moisture Tendency Equations in a Tropical Atmosphere

2005 ◽  
Vol 62 (5) ◽  
pp. 1601-1613 ◽  
Author(s):  
C. López Carrillo ◽  
D. J. Raymond
Keyword(s):  
Temperature Profile ◽  
Diagnostic Evaluation ◽  
Moisture Convergence ◽  
Tropical Atmosphere ◽  
Moisture Budget ◽  
High Confidence ◽  
Tropical Ocean ◽  
Space And Time ◽  
Toga Coare ◽  
Ocean Atmosphere

Abstract Direct diagnostic evaluation of the moisture tendency in the moisture equation is very difficult in practice because two poorly measured terms, moisture convergence and precipitation, dominate the equation. Using the near constancy in space and time of the tropical temperature profile, a variety of energy and entropy based equations have been employed to obtain indirect estimates of the moisture budget. In this paper rigorous versions of the energy and entropy equations are developed. The strengths and weakness of these two formulations are complementary, allowing the authors to estimate moistening and drying tendencies with high confidence when the two formulations are used together. This study applies the theory to data from Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). The results demonstrate how convection regulates the tropospheric humidity, drying the atmosphere when it becomes too moist, and moistening it when it becomes too dry.

scholarly journals A climatology of tropical wind shear produced by clustering wind profiles from a climate model

2021 ◽  
Author(s):  
Mark R. Muetzelfedt ◽  
Robert S. Plant ◽  
Peter A. Clark ◽  
Alison J. Stirling ◽  
Steven J. Woolnough
Keyword(s):  
Principal Components ◽  
Wind Shear ◽  
Clustering Algorithm ◽  
Climate Model ◽  
Convective Available Potential Energy ◽  
Model Output ◽  
Tropical Ocean ◽  
Toga Coare ◽  
Climate Model Output ◽  
Wind Profiles

Abstract. A procedure for producing a climatology of tropical wind shear from climate-model output is presented. The procedure is designed to find grid columns in the model where the organization of convection may be present. The climate-model output consists of east–west and north–south wind profiles at 20 equally spaced pressure levels from 1000 hPa to 50 hPa, and the Convective Available Potential Energy (CAPE) as diagnosed by the model’s Convection Parametrization Scheme (CPS). The procedure begins by filtering the wind profiles based on their maximum shear, and on a CAPE threshold of 100 J kg−1. The filtered profiles are normalized using the maximum wind speed at each pressure level, and rotated to align the wind at 850 hPa. From each of the filtered profiles, a sample has been produced with 40 dimensions (20 for each wind direction). The number of dimensions is reduced by using Principal Component Analysis (PCA), where the requirement is that 90 % of the variance must be explained by the principal components. This requires keeping the first seven leading principal components. The samples, as represented by their principal components, can then be clustered using the K-Means Clustering Algorithm (KMCA). 10 clusters are chosen to represent the samples, and the median of each cluster defines a Representative Wind Profile (RWP) – a profile that represents the shear conditions of the wind profiles produced by the climate model. The RWPs are analysed, first in terms of their vertical structure, and then in terms of their geographical and temporal distributions. We find that the RWPs have some features often associated with the organization of convection, such as low-level and mid-level shear. Some of the RWPs can be matched with wind profiles taken from case studies of organization of convection, such as squall lines seen in Tropical Ocean Global Atmosphere, Coupled Atmosphere Ocean Research Experiment (TOGA–COARE). The RWPs’ geographical distributions show that each RWP occurs preferentially in certain regions. Six of the RWPs occur preferentially over land, while three occur preferentially over oceans. The temporal distribution of RWPs shows that they occur preferentially at certain times of the year, with the distributions having mainly one or two modes. Their geographical and temporal distributions are compared with those seen in previous studies of organized convection, and some broad and specific similarities are noted. By performing the analysis on climate-model output, we lay the foundations for the development of the representation of shear-induced organization in a CPS. This would use the same methodology to diagnose where the organization of convection occurs, and modify the CPS in an appropriate manner to represent it.

scholarly journals Sensibilidade de conjuntos de nuvens a variações de parâmetros microfísicos: parte I - simulação de controle

2013 ◽  
Vol 28 (1) ◽  
pp. 13-24 ◽  
Author(s):  
André de Sena Pinheiro ◽  
Alexandre Araújo Costa
Keyword(s):  
Atmospheric Modeling ◽  
Ensemble Model ◽  
Regional Atmospheric Modeling System ◽  
Tropical Ocean ◽  
Toga Coare ◽  
Ocean Atmosphere ◽  
Regional Atmospheric Modeling

Este trabalho é o primeiro de uma série de quatro artigos, com o objetivo de analisar como variações em parâmetros microfísicos afetam o ciclo de vida de nuvens de fase mista, para diferentes condições de estabilidade vertical, adotando como ferramenta uma versão de "cloud ensemble model" - CEM do Regional Atmospheric Modeling System (RAMS). São utilizados dados do Período de Obervação Intensiva (Intensive Observing Period - IOP) do Tropical Ocean Global / Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) como forçante para o CEM. Este foi calculado para três regimes, a depender da atividade convectiva: "médio", em que foi considerada a média das variáveis para todo o IOP, "ativo" (convecção mais intensa) e "suprimido" (convecção menos pronunciada). Para cada regime, calculou-se a média das componentes zonal e meridional da velocidade do vento e as forçantes advectivas (horizontal mais vertical) de temperatura potencial e umidade específica. Tais forçantes foram assimiladas pelo CEM em diferentes testes de sensibilidade, descritos nas partes seguintes desta série de artigos. Na parte I, são apresentados os resultados referentes à simulação controle, mostrando como um CEM estabelece uma condição de quase-equilíbrio resultante da resposta da convecção às forçantes de grande escala estacionárias.

scholarly journals Impact of TMI SST on the Simulation of a Heavy Rainfall Episode over Mumbai on 26 July 2005

2008 ◽  
Vol 136 (10) ◽  
pp. 3714-3741 ◽  
Author(s):  
S. K. Deb ◽  
C. M. Kishtawal ◽  
P. K. Pal ◽  
P. C. Joshi
Keyword(s):  
Large Scale ◽  
Numerical Models ◽  
Convective Available Potential Energy ◽  
India Meteorological Department ◽  
Tropical Rainfall Measuring Mission ◽  
Atmospheric Modeling ◽  
Cumulus Parameterization ◽  
Surface Boundary ◽  
Maximum Rainfall ◽  
The Impact

In this study the simulation of a severe rainfall episode over Mumbai on 26 July 2005 has been attempted with two different mesoscale models. The numerical models used in this study are the Brazilian Regional Atmospheric Modeling System (BRAMS) developed originally by Colorado State University and the Advanced Research Weather Research Forecast (WRF-ARW) Model, version 2.0.1, developed at the National Center for Atmospheric Research. The simulations carried out in this study use the Grell–Devenyi Ensemble cumulus parameterization scheme. Apart from using climatological sea surface temperature (SST) for the control simulations, the impact of the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) SST on the simulation of rainfall is evaluated using these two models. The performances of the models are compared by examining the predicted parameters like upper- and lower-level circulations, moisture, temperature, and rainfall. The strength of convective instability is also derived by calculating the convective available potential energy. The intensity of maximum rainfall around Mumbai is significantly improved with TMI SST as the surface boundary condition in both the models. The large-scale circulation features, moisture, and temperature are compared with those in the National Centers for Environmental Prediction analyses. The rainfall prediction is assessed quantitatively by comparing the simulated rainfall with the rainfall from TRMM products and the observed station values reported in Indian Daily Weather Reports from the India Meteorological Department.

scholarly journals Observation of Moisture Tendencies Related to Shallow Convection

2015 ◽  
Vol 72 (2) ◽  
pp. 641-659 ◽  
Author(s):  
H. Bellenger ◽  
K. Yoneyama ◽  
M. Katsumata ◽  
T. Nishizawa ◽  
K. Yasunaga ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Large Scale ◽  
Numerical Models ◽  
Global Climate ◽  
Intraseasonal Variability ◽  
Lower Troposphere ◽  
Shallow Convection ◽  
Initial Attempt ◽  
Convective Clouds ◽  
Key Factor

Abstract Tropospheric moisture is a key factor controlling the global climate and its variability. For instance, moistening of the lower troposphere is necessary to trigger the convective phase of a Madden–Julian oscillation (MJO). However, the relative importance of the processes controlling this moistening has yet to be quantified. Among these processes, the importance of the moistening by shallow convection is still debated. The authors use high-frequency observations of humidity and convection from the Research Vessel (R/V) Mirai that was located in the Indian Ocean ITCZ during the Cooperative Indian Ocean Experiment on Intraseasonal Variability/Dynamics of the MJO (CINDY/DYNAMO) campaign. This study is an initial attempt to directly link shallow convection to moisture variations within the lowest 4 km of the atmosphere from the convective scale to the mesoscale. Within a few tens of minutes and near shallow convection occurrences, moisture anomalies of 0.25–0.5 g kg−1 that correspond to tendencies on the order of 10–20 g kg−1 day−1 between 1 and 4 km are observed and are attributed to shallow convective clouds. On the scale of a few hours, shallow convection is associated with anomalies of 0.5–1 g kg−1 that correspond to tendencies on the order of 1–4 g kg−1 day−1 according to two independent datasets: lidar and soundings. This can be interpreted as the resultant mesoscale effect of the population of shallow convective clouds. Large-scale advective tendencies can be stronger than the moistening by shallow convection; however, the latter is a steady moisture supply whose importance can increase with the time scale. This evaluation of the moistening tendency related to shallow convection is ultimately important to develop and constrain numerical models.

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