An investigation into the mechanisms of changes in mid-latitude mean sea level pressure as greenhouse gases are increased

The surface climate response to 11-yr solar forcing during northern winter is first reestimated by applying a multiple linear regression (MLR) statistical model to Hadley Centre sea level pressure (SLP) and sea surface temperature (SST) data over the 1880–2009 period. In addition to a significant positive SLP response in the North Pacific found in previous studies, a positive SST response is obtained across the midlatitude North Pacific. Negative but insignificant SLP responses are obtained in the Arctic. The derived SLP response at zero lag therefore resembles a positive phase of the Arctic Oscillation (AO). Evaluation of the SLP and SST responses as a function of phase lag indicates that the response evolves from a negative AO-like mode a few years before solar maximum to a positive AO-like mode at and following solar maximum. For comparison, a similar MLR analysis is applied to model SLP and SST data from a series of simulations using an atmosphere–ocean general circulation model with a well-resolved stratosphere. The simulations differed only in the assumed solar cycle variation of stratospheric ozone. It is found that the simulation that assumed an ozone variation estimated from satellite data produces solar SLP and SST responses that are most consistent with the observational results, especially during a selected centennial period. In particular, a positive SLP response anomaly is obtained in the northeastern Pacific and a corresponding positive SST response anomaly extends across the midlatitude North Pacific. The model response versus phase lag also evolves from a mainly negative AO-like response before solar maximum to a mainly positive AO response at and following solar maximum.

Changes in the thermal conditions of the ocean surface, the interface for air‐sea exchange, are critical for understanding global climate and environmental change. Here we explore the evolution of sea surface temperature (SST) and the meridional SST gradient (STG) at orbital timescales since 4 million years ago (Ma), along with interactions between SSTs, the cryosphere, and the global carbon cycle. We observe orbital eccentricity and obliquity influences on SST evolution and infer that SST changes may have played a key role in atmospheric CO2 and cryosphere changes through key climate transitions in the past 4 Ma. We find a major equator‐to‐pole STG increase in the Northern Hemisphere (NH) close to the initiation of major NH glaciation (at ∼2.7 Ma). In addition, we find substantial increases in the obliquity sensitivity (Sobl) of NH STG at ∼2.7 Ma and in Southern Hemisphere (SH) STG at ∼1 Ma, which may be responses to important expansions of NH and SH ice sheets, respectively. Phase analysis shows that SST changes typically lead global ice volume changes throughout the last 4 Ma. SST changes also lead atmospheric CO2 changes since ∼1.5 Ma, which indicates that SST changes either drove, or directly reflect, processes that changed ocean‐atmosphere carbon exchange and, thus, atmospheric CO2 concentrations. Overall, our study emphasizes that SST changes were a critical component of climate change throughout the last 4 Ma.

<p>The Pliocene - Pleistocene period (3.6-1.8 Ma) was a significant global cooling time, from very warm, equable climates to high-amplitude glacial-interglacial cycles. The origin of glaciers in the Northern Hemisphere, and the mechanisms by which glacial cycles have expanded since the late Pliocene, remain a subject of ongoing discussion. The studies of the Pliocene orbital scale climate evolution mainly are focused on marine sediments and loess-paleosoil sequences, however, there are few records of continental lacustrine facies during this period. Here we present a 37.6 m high-resolution Sanmen lacustrine sequences during the Pliocene-Pleistocene transition period that indicates the astronomically controlling East Asian climate transition and the Sanmen paloelake evolution. The Rb/Sr series evolution was divided into two parts for astronomical analysis based on the obvious changes observed in curve shape and Evolutionary spectral analysis through the section: 7.4-19 and 19-45 m. Based on evaluation of average accumulation rates from paleomagnetic results, the dominated ~99-cm cycles in the 7.4 to 19 m intervals represent ~41 kyr obliquity cycles. The 19 to 45 m intervals show obvious cycles at ~232-cm, interpreting as ~100 kyr eccentricity. Astronomical tuning combined with paleomagnetic results has been used to establish the 3.83-2.32 Ma high-precision astronomical scale. Rb/Sr series reveals that ~100 kyr eccentricity was the dominant control on lake expansion for Sanmen paleolake evolutionary before 2.75 Ma, after that, dominant obliquity control. Based on re-established the meridional sea surface temperature (SST) gradient between polar Atlantic borehole ODP 982 and the equatorial Atlantic borehole ODP 662, results show that the meridional sea surface temperature gradients increased significantly at 2.75 Ma, with cyclicity changing from the dominant ~140 kyr and ~95 kyr cycles to ~41 kyr at 2.75 Ma, and is coeval with our Rb/Sr record in the Weihe Basin. Crossspectral analysis show that the Rb/Sr and meridional SST gradient are strongly coherent and almost in-phase at these primary orbital periods in the past between 3.83-2.32 Ma. Thus, we conclude that the reorganization of the East Asian climate system at ~2.75 Ma, which coincided with the expansion of Arctic ice sheet, was a response to a dramatic cooling of the global climate and obliquity-driven changes in meridional SST gradients.</p>

Using daily National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) (1948–2009) and European Centre for Medium-Range Weather Forecasts (ECMWF) ReAnalyses (ERA)-40 (1958–2001) reanalysis mean sea level pressure (MSLP) data, the frequencies in the extremes of low/high MSLP days were computed with the 10th and 90th percentiles during the summer monsoon season (June–September) over 11 zones of India, the Arabian Sea, the Bay of Bengal and all-India as a whole. We observed that the trends in the frequencies of high (low) MSLP days are increasing (decreasing), indicating a increase/decrease in anticyclonic/cyclonic activities, respectively, which affect the monsoon performance over the Indian region. The decreasing (increasing) tendency of the frequency of the low (high) MSLP days suggests a consistency between the extreme MSLP and its associated rainfall activities. The frequency of the high MSLP days over India is highly correlated negatively with the Indian summer monsoon rainfall (ISMR). The linear trends in the frequencies of the extreme low/high MSLP days for different zones and all-India are found to be highly significant (at the 0.1% level and above). After 1978, the trends in the series of low/high MSLP days are found to be more towards decreasing/increasing tendencies, respectively, whereas the frequencies of low MSLP days are much higher than those of high MSLP days during the late 1970s. The same characteristics were also evidenced from the analysis based on ECMWF ERA-40 data for the period 1958–2001. The possible causes of this may be El Niño events, greenhouse gases (GHGs), unprecedented surface warming and also tropospheric cooling trends during recent decades over the northern hemisphere as well as over the Indian region and major volcanic eruptions that occurred during the period 1978–2009.

تغییرپذیری زمانی و مکانیشدت پرفشار سیبری ( SHI)،در دوره تشدیدگرمایش جهانی موضوع پژوهش پیش رو می‌باشد. در این راستا، از داده‌های ماهانه SLP (NCEP/NCAR Reanalysis 1)جهت استخراج شاخص SHI به عنوان بیشترین مقدار فشار در قلمرو مکانی آناستفاده شده است.با تحلیلِداده‌های آنومالی دمای سطح زمین (مرکز ملی داده‌های اقلیمی )، دو دوره متمایز قبل از سال 1973 و بعد از این سال تشخیص داده شد. در نهایت معنادار بودن تغییرات زمانی و مکانی SHI طی دو دوره مورد مطالعه، با آزمون‌های مقایسه‌ای مورد بحث و نتیجه گیری قرار گرفتند.با استخراج SHI و موقعیت مکانی مراکزِ آن در ماه‌های دسامبر، ژانویه و فوریه،مشخص شد که در دوره بعد از سال 1973(تشدیدگرمایش جهانی)، SHI تضعیف شده و دامنه تغییرات سالانه آن نسبت به دوره قبل، کاهش محسوسی داشته است که بیشتر تحت تاثیر کاهش مقادیر حداکثرSHI بوده است.همچنین مشخص شد که در این دوره، مراکز SHI به سمت 50°N و 90°E جابجا شده‌اند افزون بر آن، هم فشار5/1020 و هم فشار1034هکتوپاسکال به سمت غرب انتقال یافته‌اند، کاهش مساحت قابل ملاحظه‌ای در هم‌فشار 1034 هکتوپاسکال طی دوره تشدید گرمایش جهانی مشاهده شده است که با توجه به کاهش مقادیر حداکثر SHI قابل توجیه است.

This study focuses on the interplay between mean sea level pressure (MSLP), sea surface temperature (SST), and wind and cloudiness anomalies over the Indian Ocean in seasonal composite sequences prior to, during, and after strong, near-global El Niño and La Niña episodes. It then examines MSLP and SST anomalies in the 2–2.5-year quasi-biennial (QB) and 2.5–7-year low-frequency (LF) bands that carry the bulk of the raw ENSO signal. Finally, these fields were examined in conjunction with patterns of correlations between rainfall and joint spatiotemporal empirical orthogonal function (EOF) time series band pass filtered in the QB and LF bands. The seasonal composites indicate that the El Niño-1 (La Niña-1) pattern tends to display a more robust and coherent (weaker and less organized) structure during the evolution towards the mature stage of the event. The reverse tends to be apparent in the cessation period after the peak phase of an event, when El Niño events tend to collapse quite quickly. Climatic variables over the Indian Ocean Basin linked to El Niño and La Niña events show responses varying from simultaneous, to about one season's lag. In general, SSTs tend to evolve in response to changes in cloud cover and wind strength over both the north and south Indian Ocean. There are also strong indications that the ascending (descending) branch of the Walker circulation is found over the African continent (central Indian Ocean) during La Niña phases, and that the opposite configuration occurs in El Niño events. These alternations are linked to distinct warm–cool (cool–warm) patterns in the north–south SST dipole over the western Indian Ocean region during the El Niño (La Niña) events. An examination of MSLP and SST anomaly patterns in the QB and LF bands shows that signals are more consistent during El Niño-1 and El Niño sequences than they are during La Niña-1 and La Niña sequences. The QB band has a tendency to display the opposite anomaly patterns to that seen on the LF band during the early stages of event onset, and later stage of event cessation, during both El Niño–Southern Oscillation (ENSO) phases. El Niño events tend to be reinforced by signals on both bands up to their mature phase, but are then seen to erode rapidly, as a result of the presence of distinct La Niña anomalies on the QB band after their peak phase. During La Niña events, the opposite is observed during their cessation phase. Both QB and LF bands often display SST dipole anomalies that are not clearly evident in the raw composites alone. An eastern Indian Ocean SST dipole shows a tendency to occur during the onset phase of particular El Niño or La Niña episodes, especially during the austral autumn–winter (boreal spring–summer) and, when linked to tropical-temperate cloud bands, can influence Australian rainfall patterns. Analyses of seasonal correlations between rainfall and joint MSLP and SST EOF time series on QB and LF bands and their dynamical relationship with MSLP and SST anomalies during El Niño and La Niña events, show that the interplay between atmospheric circulation and SST anomalies dictates the observed rainfall response. Instances where either, or both, QB and LF bands are the prime influence on observed rainfall regimes are evident. This ability to discriminate the finer structure of physical relationships, correlations and patterns provides a deeper insight into Indian Ocean responses to ENSO phases. Copyright © 2000 Royal Meteorological Society

This study focuses on the interplay between mean sea level pressure (MSLP), sea surface temperature (SST), and wind and cloudiness anomalies over the Indian Ocean in seasonal composite sequences prior to, during, and after strong, near-global El Niño and La Niña episodes. It then examines MSLP and SST anomalies in the 2–2.5-year quasi-biennial (QB) and 2.5–7-year low-frequency (LF) bands that carry the bulk of the raw ENSO signal. Finally, these fields were examined in conjunction with patterns of correlations between rainfall and joint spatiotemporal empirical orthogonal function (EOF) time series band pass filtered in the QB and LF bands. The seasonal composites indicate that the El Niño-1 (La Niña-1) pattern tends to display a more robust and coherent (weaker and less organized) structure during the evolution towards the mature stage of the event. The reverse tends to be apparent in the cessation period after the peak phase of an event, when El Niño events tend to collapse quite quickly. Climatic variables over the Indian Ocean Basin linked to El Niño and La Niña events show responses varying from simultaneous, to about one season's lag. In general, SSTs tend to evolve in response to changes in cloud cover and wind strength over both the north and south Indian Ocean. There are also strong indications that the ascending (descending) branch of the Walker circulation is found over the African continent (central Indian Ocean) during La Niña phases, and that the opposite configuration occurs in El Niño events. These alternations are linked to distinct warm–cool (cool–warm) patterns in the north–south SST dipole over the western Indian Ocean region during the El Niño (La Niña) events. An examination of MSLP and SST anomaly patterns in the QB and LF bands shows that signals are more consistent during El Niño-1 and El Niño sequences than they are during La Niña-1 and La Niña sequences. The QB band has a tendency to display the opposite anomaly patterns to that seen on the LF band during the early stages of event onset, and later stage of event cessation, during both El Niño–Southern Oscillation (ENSO) phases. El Niño events tend to be reinforced by signals on both bands up to their mature phase, but are then seen to erode rapidly, as a result of the presence of distinct La Niña anomalies on the QB band after their peak phase. During La Niña events, the opposite is observed during their cessation phase. Both QB and LF bands often display SST dipole anomalies that are not clearly evident in the raw composites alone. An eastern Indian Ocean SST dipole shows a tendency to occur during the onset phase of particular El Niño or La Niña episodes, especially during the austral autumn–winter (boreal spring–summer) and, when linked to tropical-temperate cloud bands, can influence Australian rainfall patterns. Analyses of seasonal correlations between rainfall and joint MSLP and SST EOF time series on QB and LF bands and their dynamical relationship with MSLP and SST anomalies during El Niño and La Niña events, show that the interplay between atmospheric circulation and SST anomalies dictates the observed rainfall response. Instances where either, or both, QB and LF bands are the prime influence on observed rainfall regimes are evident. This ability to discriminate the finer structure of physical relationships, correlations and patterns provides a deeper insight into Indian Ocean responses to ENSO phases. Copyright © 2000 Royal Meteorological Society

Trends in the ocean–atmosphere conditions of the North Atlantic under global warming, manifested since the second half of the 20th century and intensified in the early 21st century, are identified, and their relationship with storm activity is examined. Using data from the Climate Reanalyzer platform, the spatiotemporal variability of sea surface temperature, near-surface air temperature, the thermal contrast between the ocean and the atmosphere (defined as the difference between sea surface temperature and near-surface air temperature), mean sea level pressure, and wind fields at 250 hPa, which characterize the position and intensity of the jet stream, was analyzed. Relative to the 1961–1990 climate baseline, sea surface temperature anomalies during 2021–2024 indicate widespread warming across the North Atlantic, with maximum values along the Gulf Stream and the North Atlantic Current. In contrast, anomalies relative to the 1991–2020 baseline are weaker and more spatially heterogeneous, with a persistent region of reduced warming in the subpolar North Atlantic. Seasonal analysis reveals springtime maxima along the Gulf Stream, a northward displacement of warm anomalies in summer, and predominantly weak or negative anomalies in autumn and winter. Long-term records (1940–2024) indicate accelerated warming since the 1990s, with near-surface air temperature increasing more rapidly than sea surface temperature, leading to a reduction in the ocean–atmosphere thermal contrast, particularly during winter. Wintertime (2021–2024) pressure fields exhibit negative mean sea level pressure anomalies over the central subpolar North Atlantic and higher pressure along the basin periphery, suggesting a concentration and partial reorganization of the extratropical storm track. Corresponding 250-hPa wind anomalies indicate localized jet strengthening and a northward displacement of the jet axis.

Spatio-temporal long-term evaluations of the mean sea level pressure, sea level change, and sea surface temperature over two enclosed seas

In a previous study, an intra-annual relationship of observed precipitation, manifested by negative correlations between domain-averaged spring and autumn precipitation of the same year, was found in two domains covering France and Central Europe for the period 1972–1990 (Hirschi et al., J Geophys Res 112(D22109), 2007). Here, this link and its temporal evolution over France during the twentieth century is further investigated and related to the atmospheric circulation and North Atlantic/Mediterranean sea surface temperature (SST) patterns. Observational datasets of precipitation, mean sea level pressure (MSLP), atmospheric teleconnection patterns, and SST, as well as various global and regional climate model simulations are analyzed. The investigation of observed precipitation by means of a running correlation with a 30-year time window for the period 1901–present reveals a decreasing trend in the spring-to-autumn correlations, which become significantly negative in the second half of the twentieth century. These negative correlations are connected with similar spring-to-autumn correlations in observed MSLP, and with negatively correlated spring East Atlantic (EA) and autumn Scandinavian (SCA) teleconnection pattern indices. Maximum covariance analyses of SST with these atmospheric variables indicate that at least part of the identified spring-to-autumn link is mediated through SST, as spring precipitation and MSLP are connected with the same autumn SST pattern as are autumn precipitation, MSLP and the SCA pattern index. Except for ERA-40 driven regional climate models from the EU-FP6 project ENSEMBLES, the analyzed regional and global climate models, including Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) simulations, do not capture this observed variability in precipitation. This is associated with the failure of most models in simulating the observed correlations between spring and autumn MSLP. While the causes for the identified relationship cannot be fully established its timing suggests a possible link with increased aerosol loading in the global dimming period.

Currently, the mechanisms for Pacific Decadal Oscillation (PDO) are still disputed, and in particular the atmosphere response to the ocean in the mid-latitude remains a key uncertainty. In this study, we investigate two potential feedbacks—a local positive and a delayed negative—for the PDO based on a long-term control simulation using the ECHAM5/MPI-OM coupled model, which is selected because of reproduces well the variability of PDO. The positive feedback is as follows. In the PDO positive phase, the meridional sea surface temperature (SST) gradient is intensified and this strengthens the lower level atmospheric baroclinicity in the mid-latitudes, leading to the enhancement of Aleutian low and zonal wind. These atmospheric changes reinforce the meridional SST temperature gradient through the divergence of ocean surface currents. The increased heat flux loss over the anomalously warm water and decreased heat flux loss over the anomalously cold water in turn reinforce the lower atmospheric meridional temperature gradient, baroclinicity and atmospheric circulation anomalies, forming a local positive feedback for the PDO. The delayed negative feedback arises, because the intensified meridional SST gradient also generates an anticyclonic wind stress in the central North Pacific, warming the upper ocean by Ekman convergence. The warm upper ocean anomalies then propagate westward and are transported to the mid-latitudes in the western North Pacific by the western boundary current. This finally reduces the meridional SST gradient, 18 years after the peak PDO phase. These results demonstrate the significant contributions of the meridional SST gradient to the PDO’s evolution.

We compute the atmospheric heat transport in a realistic atmospheric general circulation modelunder five different configurations of implied heat transport in the ocean. The implied oceanicheat transport is varied by changing the meridional gradient of sea surface temperature (SST).Climatological SSTs are employed for the control run. The other runs differ in that a zonallysymmetric component is added to or subtracted from the climatological SST field. The meridionalstructure of the variation in SST gradient is based on the observed change in zonallyaveraged SST over the last century. The SST trend has maxima of about 1 K at high latitudesof both hemispheres. Elsewhere, the change in SST over the last century is fairly uniform atabout 0.5 K. We find that in the annual mean, the atmosphere adjusts so that the total meridionalheat transport (by atmosphere and ocean) is rather insensitive to the change in zonally averaged SST. Interannual variability in the annual mean heat transport is minor in each of these cases. There is a large degree of compensation even between the different components of atmosphericheat transport such that changes in latent heat transport usually go hand in hand with changesin dry static energy transport of an opposite sign. The radiative flux at the top of the atmosphereis affected the most by the change in SST in the tropics, where the shortwave component showsa strong negative feedback and the longwave component shows a weak positive feedback. Concentrating on the winter season in the Northern Hemisphere, we find that when we decreasethe meridional SST gradient (i.e., warm the sea surface at high latitudes the most), the stationarywaves accomplish more of the poleward heat transport than before. When we increase themeridional SST gradient, the heat flux due to both transient and stationary waves increases, although not by nearly as much as most eddy parameterization schemes would predict. Thewinter season in the Southern Hemisphere shows a substantial increase in heat transport bytransient waves when the meridional SST gradient is increased. Their maximum heat transportis greater and extends over a wider band of latitudes than in the control case. Because theSouthern Hemisphere is mostly covered by ocean, the stationary waves are weak and play aminor roôle in atmospheric heat transport.

Understanding natural atmospheric decadal variability is an important element of climate research, and here we investigate the geographic and seasonal diversity in the balance between its competing sources. Data are provided by an ensemble of multi-decadal atmospheric general circulation model experiments, forced by observed sea surface temperatures (SSTs), and verified against observations. First, the nature of internal atmospheric variability is studied. By assessing its spectral character, we refute the idea that internal modes may persist or oscillate on multi-annual time-scales, either through mechanisms purely internal to the atmosphere, or via coupling to the land surface; instead, they behave as a white noise process. Second, and more importantly, the role of oceanic forcing, relative to internal variability, is investigated by extending the ‘analysis of variance’ technique to the frequency domain. Significance testing and confidence intervals are also discussed. In the tropics, atmospheric decadal variability is usually dominated by oceanic forcing, although for some regions less so than at interannual time-scales. A moderate oceanic impact is also found for some extratropical regions in some seasons. Verification against observed mean sea-level pressure (MSLP) data suggests that many of these influences are realistic, although some model errors are also revealed. In other mid- and high-latitude regions, local simulated decadal variability is dominated by random processes, i.e. the integrated effects of chaotic weather systems. Third, we focus on the mechanisms of decadal variability in two specific regions (where the model is well behaved). Over the tropical Pacific, the relative impact of SSTs on decadal MSLP is strongly seasonal such that it peaks in September to November (SON). This is explained by noting that the model atmosphere is responsive to SSTs a little farther west in SON than it is in other seasons, and here it picks up relatively more decadal power from the ocean (the western Pacific being less dominated by ENSO time-scales), causing atmospheric ‘signal-to-noise ratios’ to be enhanced at decadal timescales in SON. Over southern North America, a strong SST impact is found in summer and autumn, resulting in an upward trend of MSLP over recent decades. We suggest this is caused by decadal SST variability in the Caribbean (and to some extent the tropical northeast Pacific in summer), which induces anomalous convective heating over these regions and hence the wider MSLP response.

Sea surface temperature history of the low latitude western Pacific during the last 5.3 million years

Map of the natural zones of the ocean: Okeanologiya 1961. 1 (5) : 941–943