Category: Spatial variability of intraseasonal sst

Li, Y. Han, W. Wang, and M. The MISOs induce intraseasonal SST variability primarily through surface heat flux forcing, contributed by both shortwave radiation and turbulent heat flux, and secondarily through mixed layer entrainment. It means that the ocean state of the EAS region during the developing stage favors active two-way air—sea interaction and the formation of the strong first-pulse MISO event.

These results provide compelling evidence for the vital role played by the ocean in the MISO mechanisms and have implications for understanding and forecasting the ISM onset. During boreal summer, the north Indian Ocean is dominated by prevailing southwesterly winds and heavy rainfall Fig. The ISM, as a major component of the Asian monsoon system, has profound impacts on the agriculture, economy, and environment of South and Southeast Asian countries e.

Accurate prediction of the ISM rainfall is of paramount importance for agriculture planning and society adaptation and therefore a major task for climate researchers. The ISM system, however, exhibits strong and complicated variability over a wide range of time scales, which makes its simulation and prediction rather challenging for climate models e.

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One substantial component of the ISM rainfall variability is at the intraseasonal time scale, which typically manifests as fluctuations between active spells with good rainfall and break spells with little rainfall over India Goswami and Ajaya Mohan ; Webster et al. Prolonged or frequent breaks can cause widespread drying over South Asia and lead to substantial agricultural yield reduction.

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The active and break spells are closely associated with the large-scale atmospheric intraseasonal oscillations, referred to as the monsoon intraseasonal oscillations MISOs; Yasunari Some of them are associated with the eastward-propagating Madden—Julian oscillations along the equator e. Many mechanisms have been proposed to understand the MISO dynamics. At the lowest order the MISO is considered as an internal instability mode of the tropical atmosphere e.

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For example, Jiang et al. According to Jiang et al. On the other hand, air—sea interaction has been shown to play an important role in MISO dynamics e. The warm SST to the north of the convection center can destabilize the lower atmosphere and lead to the northward movement of the convection system Kemball-Cook and Wang ; Harrison and Vecchi ; Roxy and Tanimoto The importance of air—sea interaction, especially the SST feedbacks to the atmosphere, in the MISO dynamics has been confirmed by modeling studies Fu et al.

Li et al. The mini warm pool of the Arabian Sea formed in spring is the primary moisture source for the ISM rainfall Ninomiya and Kobayashi Xi et al.

spatial variability of intraseasonal sst

Roxy et al. Intraseasonal SST variability and relevant upper-ocean processes in the Arabian Sea deserve more attention from the climate community. The present study is mainly motivated by three objectives. First, we aim to provide a comprehensive description of the intraseasonal SST and precipitation variability during the ISM, underscoring its unique characteristics in the Arabian Sea.

Given the importance of the initial condition in the extended-range forecast of the ISM Goswami and Gouda ; Abhilash et al. Second, we attempt to gain insights into the upper-ocean processes controlling intraseasonal SST variability in the Arabian Sea.Legaard and Andrew C. We define intraseasonal variability as temporal variation remaining after removal of interannual variability and stationary seasonal cycles. Semivariograms are used to quantify the temporal structure of residual time series.

Empirical orthogonal function EOF analyses of semivariograms calculated across the region isolate dominant scales and corresponding spatial patterns of intraseasonal variability.

Spatial amplitudes and patterns of intraseasonal variance derived from mode 1 suggest dominant forcing of intraseasonal variability through distortion of large scale chlorophyll and SST gradients by mesoscale circulation. Chlorophyll variance is greatest over the shelf and slope, with elevated values closely confined to the Baja shelf and extending farthest from shore off California and the Pacific Northwest. Intraseasonal contributions to total SST variability are strongest near upwelling centers off southern Oregon and northern California, where seasonal contributions are weak.

Intraseasonal variability accounts for the majority of total chlorophyll variance in most inshore areas save for southern Baja, where seasonal cycles dominate. Contributions of higher EOF modes to semivariogram structure indicate the degree to which intraseasonal variability is shifted to shorter timescales in certain areas. Comparisons of satellite-derived SST semivariograms to those calculated from co-located and concurrent buoy SST time series show similar features.

spatial variability of intraseasonal sst

Citation: Legaard, K. ThomasSpatial patterns of intraseasonal variability of chlorophyll and sea surface. Documents: Advanced Search Include Citations. LegaardAndrew C. Citations: 1 - 0 self. Abstract [1] Six years of daily satellite data are used to quantify and map intraseasonal variability of chlorophyll and sea surface temperature SST in the California Current.

Powered by:.Jones, C. Waliser, and C. The Madden—Julian oscillation MJO involves pronounced variations in convection and large-scale circulation throughout the tropical troposphere. In addition, the MJO is also related to dynamic and thermodynamic variability near the surface and the upper ocean. This study uses observational data to characterize the changes in surface heat fluxes and sea surface temperature SST during the life cycle of the MJO. Variations in convective activity are described with outgoing longwave radiation OLR during the period January through September The prevailing conditions in the region of positive Q anomalies favor the development of positive SST anomalies, which lead to variations of enhanced convection.

spatial variability of intraseasonal sst

These conditions induce negative Q anomalies, which favor the formation of negative SST anomalies. The above results suggest a possible feedback between the oscillation and intraseasonal variations in SST and this may be an important mechanism for numerical simulations of the life cycle of the MJO. On intraseasonal timescales 30—60 daysthe Madden—Julian oscillation MJO is the primary mode in the tropical atmosphere Madden and Julian Since its discovery by Madden and Julian over two decades ago, the MJO has continued to be a topic of significant interest due to the wide range of phenomena it interacts with.

These include interaction with the extratropics, which may influence weather forecasts on medium and extended ranges Chen and Alpert ; Ferranti et al. Studies of near-surface parameters and upper ocean have also detected the MJO signature Krishnamurti et al.

Wang and Ruifor example, pointed out that the annual cycle of SST in the Indian Ocean monsoon region can be a determining factor in the spatial and annual variations of the MJO. Furthermore, in a theoretical work, Li and Wang considered the effect of meridional gradients of SST on intraseasonal variations and showed that the northward and southward propagation of intraseasonal modes are sensitive to the spatial variability of SST.

Kessler et al. Their analysis shows that westerly wind bursts following a succession of eastward propagating MJO convective anomalies excite oceanic Kelvin waves that propagate farther east across the basin. Previous studies have provided some insight on the atmosphere—ocean coupling on intraseasonal timescales. The objective of this study is to examine the observed large-scale patterns of surface heat fluxes and SST anomalies during the life cycle of the MJO.

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A thorough understanding of the interaction of the MJO with the surface energy balance is important for a variety of reasons. Because the MJO involves eastward propagating modes, the oscillation has spatial patterns that are asymmetrical in the zonal direction HS The zonal asymmetry of the MJO introduces complex modifications in the components of the surface energy balance. Although this topic has been sparsely addressed in previous observational studies Kawamura ; Krishnamurti et al.International audienceThe SST-precipitation relationship in the intraseasonal variability ISV over the Asian monsoon region is examined using recent high quality satellite data and simulations from a state of the art coupled model, the climate forecast system version 2 CFSv2.

CFSv2 demonstrates high skill in reproducing the spatial distribution of the observed climatological mean summer monsoon precipitation along with its interannual variability, a task which has been a conundrum for many recent climate coupled models. The model also exhibits reasonable skill in simulating coherent northward propagating monsoon intraseasonal anomalies including SST and precipitation, which are generally consistent with observed ISV characteristics.

Results from the observations and the model establish the existence of spatial variability in the atmospheric convective response to SST anomalies, over the Asian monsoon domain on intraseasonal timescales. The intraseasonal SST anomalies result in a similar atmospheric response across the basins, which consists of a destabilization of the bottom of the atmospheric column, as observed from the equivalent potential temperature anomalies near the surface.

However, the presence of a relatively strong surface convergence over the Arabian Sea, due to the presence of a strong zonal gradient in SST, which accelerates the upward motion of the moist air, results in a relatively faster response in terms of the local precipitation anomalies over the Arabian Sea than over the Bay of Bengal and South China Sea.

With respect to the observations, the ocean-atmosphere coupling is well simulated in the model, though with an overestimation of the intraseasonal SST anomalies, leading to an exaggerated SST-precipitation relationship.

A detailed examination points to a systematic bias in the thickness of the mixed layer of the ocean model, which needs to be rectified. A too shallow deep mixed layer enhances suppress the amplitude of the intraseasonal SST anomalies, thereby amplifying lessening the ISV and the active-break phases of the monsoon in the model.

Location of Repository. Preethi, Pascal Terray and R. Suggested articles.Thesis directed by Professor Peter Webster. The South Asian monsoon exhibits pronounced intraseasonal variability on timescales ranging from a few days to more than a month. A principal purpose of this study is to provide a comprehensive analysis of the low-frequency 25 to 80 days monsoon intraseasonal variability and to determine its structure in both space and time.

Large-scale active and break periods of rainfall are associated with the slowly evolving Intraseasonal Oscillation ISO that is characterized during northern summer by an apparent northward propagation of convection emanating from the central equatorial Indian Ocean.

The northern winter ISO is dominated by steady eastward propagation of equatorial convection and lacks significant poleward propagation and therefore is examined in the context of comparison with the summer ISO. A cross-correlation and lagged regression analysis is utilized to investigate the temporal and spatial evolution of convection and large-scale circulation patterns associated with the ISO.

Outgoing longwave radiation OLR filtered to eastward wavenumbers 1 to 3 and periods 25 to 80 days is used as the predictor for two independent regression analyses which focus on the northern summer JJAS and northern winter DJFM periods, respectively.

The evolution of ISO convection and the large-scale circulation in northern summer appears similar in many respects to that of northern winter and can be thought of in terms of propagating equatorial modes. Surface frictional convergence into a Rossby cell that is excited by equatorial ISO convection generates a band of convection that is oriented southeast to northwest and stretches from the equator to about 20 o N.

Viewed along any meridian the mode appears to propagate northward while equatorial convection propagates to the east. The summer ISO is examined in further detail and is found to contain two predominant modes of evolution that occur with approximately the same frequency.

The two modes differ primarily in how the equatorial Indian Ocean convection develops.

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The first mode exhibits an initially stationary development of low-frequency equatorial Indian Ocean convection 23 events while the second mode evolves as a steady eastward propagation of convection 27 events.

Both modes are characterized by northward propagation onto the Indian subcontinent subsequent to the development of strong convection at around 90o E. In all cases, northward propagation does not occur in the absence of eventual eastward propagation of convection along the equator. Interannual variations of summertime ISO activity are investigated.

Interannual variations in ISO activity are found to be related to year-to-year changes in the number of discrete events rather than changes in the characteristic period. Seasons characterized by strong and numerous ISOs exhibit significantly more low precipitation days and consequently deficient seasonal rainfall totals than seasons characterized by little or no ISO activity.

The summertime ISO activity does exhibit a reasonably strong inverse relationship with South Asian monsoon strength. Over the year period examined here, the relationship between South Asian monsoon strength and ISO activity is stronger than its well documented relationship with ENSO.

The year-to-year variations of ISO activity also exhibit a clear biennial timescale suggesting that the tropospheric biennial oscillation TBO may play a role in determining ISO activity although the physical mechanism is not readily apparent.

A second dominant mode of intraseasonal variability is made up of synoptic-scale westward propagating convective disturbances with timescales between 5 and 10 days.

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During the active ISO phase over India, westward propagating synoptic-scale wave activity is above normal.Thanks for helping us catch any problems with articles on DeepDyve. We'll do our best to fix them. Check all that apply - Please note that only the first page is available if you have not selected a reading option after clicking "Read Article".

Include any more information that will help us locate the issue and fix it faster for you. The SST-precipitation relationship in the intraseasonal variability ISV over the Asian monsoon region is examined using recent high quality satellite data and simulations from a state of the art coupled model, the climate forecast system version 2 CFSv2. CFSv2 demonstrates high skill in reproducing the spatial distribution of the observed climatological mean summer monsoon precipitation along with its interannual variability, a task which has been a conundrum for many recent climate coupled models.

The model also exhibits reasonable skill in simulating coherent northward propagating monsoon intraseasonal anomalies including SST and precipitation, which are generally consistent with observed ISV characteristics.

Results from the observations and the model establish the existence of spatial variability in the atmospheric convective response to SST anomalies, over the Asian monsoon domain on intraseasonal timescales.

The intraseasonal SST anomalies result in a similar atmospheric response across the basins, which consists of a destabilization of the bottom of the atmospheric column, as observed from the equivalent potential temperature anomalies near the surface.

However, the presence of a relatively strong surface convergence over the Arabian Sea, due to the presence of a strong zonal gradient in SST, which accelerates the upward motion of the moist air, results in a relatively faster response in terms of the local precipitation anomalies over the Arabian Sea than over the Bay of Bengal and South China Sea. With respect to the observations, the ocean—atmosphere coupling is well simulated in the model, though with an overestimation of the intraseasonal SST anomalies, leading to an exaggerated SST-precipitation relationship.

A detailed examination points to a systematic bias in the thickness of the mixed layer of the ocean model, which needs to be rectified. A too shallow deep mixed layer enhances suppress the amplitude of the intraseasonal SST anomalies, thereby amplifying lessening the ISV and the active-break phases of the monsoon in the model. Climate Dynamics — Springer Journals. Enjoy affordable access to over 18 million articles from more than 15, peer-reviewed journals.

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You can change your cookie settings through your browser. Open Advanced Search. DeepDyve requires Javascript to function.Six years of daily satellite data are used to quantify and map intraseasonal variability of chlorophyll and sea surface temperature SST in the California Current. We define intraseasonal variability as temporal variation remaining after removal of interannual variability and stationary seasonal cycles.

spatial variability of intraseasonal sst

Semivariograms are used to quantify the temporal structure of residual time series. Empirical orthogonal function EOF analyses of semivariograms calculated across the region isolate dominant scales and corresponding spatial patterns of intraseasonal variability. Spatial amplitudes and patterns of intraseasonal variance derived from mode 1 suggest dominant forcing of intraseasonal variability through distortion of large scale chlorophyll and SST gradients by mesoscale circulation.

Chlorophyll variance is greatest over the shelf and slope, with elevated values closely confined to the Baja shelf and extending farthest from shore off California and the Pacific Northwest. Intraseasonal contributions to total SST variability are strongest near upwelling centers off southern Oregon and northern California, where seasonal contributions are weak. Intraseasonal variability accounts for the majority of total chlorophyll variance in most inshore areas save for southern Baja, where seasonal cycles dominate.

Contributions of higher EOF modes to semivariogram structure indicate the degree to which intraseasonal variability is shifted to shorter timescales in certain areas. Comparisons of satellite-derived SST semivariograms to those calculated from co-located and concurrent buoy SST time series show similar features.

Legaard, K. Marine Sciences Faculty Scholarship. Journal of Geophysical Research-Oceans. Advanced Search. Rebecca Van Beneden. Peter Jumars. Lee Karp-Boss. Neal Pettigrew. Home My Account Accessibility Statement. Skip to main content.

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Document Type Article. Authors K. Repository Citation Legaard, K. Version publisher's version of the published document.


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