Sea-level Pressure Distribution Research Articles

Current and projected hydroclimatic changes in the Baltic and Arctic sea basins in the territories of Belarus and Russia

The article presents an assessment of current changes in air temperature, precipitation, snow and river runoff in the Baltic and Arctic Seas basins in the territories of Belarus and Russia. It is shown that the observed positive air temperature trends during the winter season are associated with the sea level pressure distribution in the North Atlantic and NAO indices. In summer, the temperature growth is correlated strongly with the Atlantic multi-decadal oscillation. Changes in the precipitation regime are synchronized with an increase in the sea level pressure in the baroclinic active zones of the Atlantic Ocean, which led to the precipitation increase in Europe since the second half of the 20th century. Interdecadal precipitation fluctuations in the study region are associated with the dynamics of the circumpolar vortex and Arctic oscillation (AO) indices. In winter, a precipitation increase is observed in the negative AO phase and is caused by an increase in the frequency of southern cyclones. In summer, when the AO phase is negative, the cyclonic activity decreases, and the precipitation growth is associated with convective processes in the atmosphere. Snow precipitation and snow water equivalent are decreasing during recent decades due the air temperature significant growth. That led to the spring floods height decreasing in the region. In the next 30 years, a decrease in the winter air temperature in the Baltic Sea basin and its increase in the Arctic Sea are expected. In summer, the air temperature increase will slow down on the descending AMO branch in the coming decades. In the precipitation regime, the growth of seasonal and daily total precipitation is expected.

Prediction of Track of Super Cyclone Amphan using WRF-ARW Model

An attempt has been made to study the prediction of the track of Super Cyclone (SuC) Amphan that formed on 13 May over Southeast Bay of Bengal (BoB) and made landfall to West Bengal-Bangladesh Coast on 20 May 2020 using Advanced Research WRF (ARW) dynamics of Weather Research and Forecasting (WRF) model. Model integration has been carried out using two-way interactive nesting domains with resolutions of 27 km for domain 1 and 9 km for domain 2 respectively covering the Bay of Bengal. Simulations are performed at an interval of 6 hours with ICs using the National Centre for Environmental Prediction (NCEP) global forecast system (GFS) 0.25° analysis and forecasts. To understand the applicability of the model in predicting the track along with landfall position and landfall time, nine real-time numerical forecasts have been carried out with model simulation starting at 00 UTC of 13 May, 14 May, 15 May, 16 May, 17 May, 18 May, 19 May, 20 May and 21 May 2020. The experiments with initial time on 16 May, 17 May, 18 May, 19 May, and 20 May 2020 have produced the best performance for the track and intensity prediction which are comparable to those provided by Bangladesh Meteorological Department (BMD) and Regional Specialized Meteorological Centre (RSMC). The tracks are produced based on the distribution of sea level pressure and vorticity. The model shows that the track prediction accuracy increases as the lead time decreases with the updated ICs. The results obtained from the model are in good agreement with the reported data. The experiment of SuCAmphan produced better track and intensity predictions with lead-time of 144, 120, 96, 48, and 24 hours. The results demonstrate that the model is capable to produce the track of SuCAmphan with reasonable accuracy. The Dhaka University Journal of Earth and Environmental Sciences, Vol. 10(2), 2021, P 35-42

Trends and variability in polar sea ice, global atmospheric circulations, and baroclinicity.

We analyze the polar sea ice distribution and the global sea level pressure (SLP) and baroclinicity distributions over the "satellite" period of 1979-2020. In the Arctic, there are statistically significant sea ice extent (SIE) decreases in all calendar months, and the annual mean has lost 2.22 million km2 over the four decades. The Antarctic SIE, in marked contrast, increased up to 2014, then commenced a remarkable retreat (the annual mean ice extent decreased by 2.03 million km2 in the 3 years to 2017), and subsequently increased to near its long-term average value in 2020. The shifts in seasonal-mean SLP patterns are consistent with a warming planet. At the synoptic scale, we diagnose the changes in the baroclinicity, the mechanism by which cyclones, fronts, and other weather systems are generated. Through a novel presentation, we give an overview of the relative roles of changes in the vertical shear and static stability in influencing the global trends in baroclinicity. In both the Arctic and Antarctic regions, baroclinicity is shown to have increased in each season (with the sole exception of the Arctic in summer). This increase, coupled with midlatitude decreases in baroclinicity, results in poleward shifts of the storm tracks.

How could a difference of 0.5°C in global warming modify the mean and extreme climate conditions around Antarctica?

AbstractThis paper quantifies the potential benefit of limiting the global warming to 1.5°C above the preindustrial level on the high‐latitude climate of the Southern Hemisphere compared to 2.0°C and above. A set of Coupled Model Intercomparison Project Phase 5 global climate model experiments is used in order to determine the mean projected changes in surface air temperature, sea level pressure, surface winds and sea ice distribution over and around Antarctica. Alongside, changes in selected variables related to extremes (such as the annual number of extremely cold mornings and extremely cold days) are also quantified as a function of the Representative Concentration Pathway (RCP) considered reaching the given warming threshold. Physical mechanisms for the projected variations in sea ice are proposed, including surface air temperature, changes in low‐level air temperature advection and meridional winds. Results show that there would be significant differences in the atmospheric and sea ice variable changes depending on the warming threshold and RCP considered, and that indeed keeping the global warming under 1.5°C could have a noticeable impact particularly on the distribution of sea ice over the Southern Ocean.

Impact of the astronomical lunar 18.6-yr tidal cycle on El-Ni\xf1o and Southern Oscillation

Even though El-Niño and Southern Oscillation (ENSO) has a tremendous impact on global climate and society, its long-term forecast remains difficult. In this study, we discovered a statistically significant relationship between ENSO timing and the 18.6-year period lunar tidal cycle in the mature-phase (December–February) ENSO time-series during 1867–2015 and extending back to 1706 with proxy data. It was found that El-Niño tended to occur in the 1st, 10th, and 13th years after the maximum diurnal tide in the 18.6-yr cycle, and La-Niña tended to occur in the 3rd, 12th, and 16th years. These tendencies were also confirmed by corresponding sea-surface temperature (SST) and sea-level pressure (SLP) distributions; particularly Pacific SST and SLP spatial patterns in the third La-Niña and the tenth El-Niño year well resemble those of Pacific Decadal Oscillation (PDO). These findings contribute to understanding and forecasting long-term ENSO variability.

Response of Tropical Cyclone Activity and Structure to Global Warming in a High-Resolution Global Nonhydrostatic Model

Future changes in tropical cyclone (TC) activity and structure are investigated using the outputs of a 14-km mesh climate simulation. A set of 30-yr simulations was performed under present-day and warmer climate conditions using a nonhydrostatic icosahedral atmospheric model with explicitly calculated convection. The model projected that the global frequency of TCs is reduced by 22.7%, the ratio of intense TCs is increased by 6.6%, and the precipitation rate within 100 km of the TC center increased by 11.8% under warmer climate conditions. These tendencies are consistent with previous studies using a hydrostatic global model with cumulus parameterization. The responses of vertical and horizontal structures to global warming are investigated for TCs with the same intensity categories. For TCs whose minimum sea level pressure (SLP) reaches less than 980 hPa, the model predicted that tangential wind increases in the outside region of the eyewall. Increases in the tangential wind are related to the elevation of the tropopause caused by global warming. The tropopause rise induces an upward extension of the eyewall, resulting in an increase in latent heating in the upper layers of the inclined eyewall. Thus, SLP is reduced underneath the warmed eyewall regions through hydrostatic adjustment. The altered distribution of SLP enhances tangential winds in the outward region of the eyewall cloud. Hence, this study shows that the horizontal scale of TCs defined by a radius of 12 m s−1 surface wind is projected to increase compared with the same intensity categories for SLP less than 980 hPa.

AMSR2 all-sky radiance assimilation and its impact on the analysis and forecast of Hurricane Sandy with a limited-area data assimilation system

A method to assimilate all-sky radiances from the Advanced Microwave Scanning Radiometer 2 (AMSR2) was developed within the Weather Research and Forecasting (WRF) model's data assimilation (WRFDA) system. The four essential elements are: (1) extending the community radiative transform model's (CRTM) interface to include hydrometeor profiles; (2) using total water Qt as the moisture control variable; (3) using a warm-rain physics scheme for partitioning the Qt increment into individual increments of water vapour, cloud liquid water and rain; and (4) adopting a symmetric observation error model for all-sky radiance assimilation.Compared to a benchmark experiment with no AMSR2 data, the impact of assimilating clear-sky or all-sky AMSR2 radiances on the analysis and forecast of Hurricane Sandy (2012) was assessed through analysis/forecast cycling experiments using WRF and WRFDA's three-dimensional variational (3DVAR) data assimilation scheme. With more cloud/precipitation-affected data being assimilated around tropical cyclone (TC) core areas in the all-sky AMSR2 assimilation experiment, better analyses were obtained in terms of the TC's central sea level pressure (CSLP), warm-core structure and cloud distribution. Substantial (>20 %) error reduction in track and CSLP forecasts was achieved from both clear-sky and all-sky AMSR2 assimilation experiments, and this improvement was consistent from the analysis time to 72-h forecasts. Moreover, the all-sky assimilation experiment consistently yielded better track and CSLP forecasts than the clear-sky did for all forecast lead times, due to a better analysis in the TC core areas. Positive forecast impact from assimilating AMSR2 radiances is also seen when verified against the European Center for Medium-Range Weather Forecasts (ECMWF) analysis and the Stage IV precipitation analysis, with an overall larger positive impact from the all-sky assimilation experiment.

Interdecadal variability of El Niño onset and its impact on monsoon systems over areas encircling the Pacific Ocean

Based on previous study by Xu and Chan (J Clim 14:418–433, 2001), two types of El Nino distinguished by the onset time, a Spring (SP) type and a Summer (SU) type, have been investigated from 1871 through 2011. As can be classified by the spatial patterns of sea surface temperature anomaly into the Warm Pool (WP) and Cold Tongue (CT) El Nino, the temporal features of the CT are dominated by the SP events whereas the SU events mostly display the spatial pattern of WP or Mixed events. The approximate 140-year data analysis shows that the frequency of SP events tends to increase in the most recent 30 years (1980–2009) while the SU events show very strong activity in the beginning of the twentieth century (1900–1929), which are closely associated with the decadal changes in oceanic and atmospheric background conditions. The air-sea processes indicate that the pattern of sea surface temperature (SST) gradient between tropical and extratropical Pacific Ocean on decadal time scales is related to the sea level pressure distribution, which tends to produce wind anomalies. The wind anomalies in turn affect the SST anomalies on inter-annual time scales over the equatorial areas and finally result in the early onset of El Nino in SP time or late onset of El Nino in SU time. A spring onset El Nino favors a Kelvin wave that propagates across the basin and a summer onset favors a Kelvin wave that does not traverse the basin or the related effects are not strong enough. The early or late onset of El Nino significantly impacts the precipitation distribution correlated with the monsoon systems including the Asian–Australian monsoon and North–South American monsoon. The El Nino–monsoon relationship is modulated by decadal changes in atmospheric and oceanic background conditions. The precipitation in the monsoonal area circling the Pacific Ocean exhibits characteristic quasi-biennial variations that are closely associated with the onset time of El Nino events, especially with the early onset of El Nino. For the Spring (SP) type, drought is observed over the central China, Australia, southwestern North America and northern South America in boreal summer, but the opposite pattern appears in the subsequent summer of the following year.

Interdecadal increase of haze in winter over North China and the Huang-huai Area and the weakening of the East Asia Winter Monsoon

The relationship between the interdecadal increase of haze in winter over North China and the Huang-huai area (HW-NCHH) and the weakening of the East Asia Winter Monsoon (EAWM) was investigated. The trend of the HW-NCHH showed significant interdecadal variation with a slow increase from 1961 to 1970, rapid increase from 1971 to 1985, and slight decrease thereafter. The HW-NCHH trend was influenced considerably but not monotonically by the emission of pollution. Based on an 11-year running mean, the correlation coefficient between the HW-NCHH and EAWM was -0.77, above the 95% confidence level. Therefore, the EAWM should be considered a factor that has important influence on the HW-NCHH over the decadal scale. Compared with the climatic state from 1961 to 1970, the EAWM was clearly weaker from 1986 to 2010 and the horizontal and vertical circulations adverse to pollution diffusion. The distribution of sea level pressure was typical of the positive phase of the Arctic Oscillation, and thus cold air was restricted to the Arctic. The surface wind and humidity both presented negative anomalies over the NCHH area, which favored the production of haze. The meridional circulation in the high latitudes was weak and zonal circulation occupied the NCHH area, which prevented the advection of cold air southward to disperse the particulate matter in the NCHH area. Meanwhile, vertical diffusion was inhibited by an anomalous high pressure and thermal inversion potential over the NCHH area, such that the particulate matter gathered within a shallow layer, which exacerbated the concentration of pollution.

Dynamical downscaling of CMIP5 global circulation models over CORDEX-Africa with COSMO-CLM: evaluation over the present climate and analysis of the added value

In this work we present the results of the application of the consortium for small-scale modeling (COSMO) regional climate model (COSMO-CLM, hereafter, CCLM) over Africa in the context of the coordinated regional climate downscaling experiment. An ensemble of climate change projections has been created by downscaling the simulations of four global climate models (GCM), namely: MPI-ESM-LR, HadGEM2-ES, CNRM-CM5, and EC-Earth. Here we compare the results of CCLM to those of the driving GCMs over the present climate, in order to investigate whether RCMs are effectively able to add value, at regional scale, to the performances of GCMs. It is found that, in general, the geographical distribution of mean sea level pressure, surface temperature and seasonal precipitation is strongly affected by the boundary conditions (i.e. driving GCMs), and seasonal statistics are not always improved by the downscaling. However, CCLM is generally able to better represent the annual cycle of precipitation, in particular over Southern Africa and the West Africa monsoon (WAM) area. By performing a singular spectrum analysis it is found that CCLM is able to reproduce satisfactorily the annual and sub-annual principal components of the precipitation time series over the Guinea Gulf, whereas the GCMs are in general not able to simulate the bimodal distribution due to the passage of the WAM and show a unimodal precipitation annual cycle. Furthermore, it is shown that CCLM is able to better reproduce the probability distribution function of precipitation and some impact-relevant indices such as the number of consecutive wet and dry days, and the frequency of heavy rain events.

東アジア地域における海面気圧分布パターンの客観分類

将来の地域気候予測に用いる統計ダウンスケーリング手法に利用するため，東アジア地域における海面気圧分布パターンの客観分類を行い，寒候期を対象として，平均分布型，出現の卓越季節，従来手法による分類結果などを参照し，得られた各パターンの特徴を明らかにした．本手法は，分布パターンを主成分スコアという客観指標に置き換え，主成分空間内でクラスター分析によりこれを分類するものである．対象領域における30年間(1979～2008年: 10958日)の午前9時の海面気圧分布パターン分類を行った結果，寒候期のパターンは強い冬型(3グループ)，弱い冬型(3)，低気圧型(1)，移動性高気圧型(2)，移動性高気圧・低気圧型(2)，その他(1)の12のグループに分類された．各グループの継続性，グループ間の移行特性(特定のグループから特定のグループへの移行しやすさ，しにくさ)について，確率を用いて定量的に明らかにした．

Seasonal and inter-annual variations of the primary types of the Arctic sea-ice drifting patterns

Monthly mean sea ice motion vectors and monthly mean sea level pressure (SLP) for the period of 1979—2006 are investigated to understand the spatial and temporal changes of Arctic sea-ice drift. According to the distinct differences in monthly mean ice velocity field as well as in the distribution of SLP, there are four primary types in the Arctic Ocean: Beaufort Gyre+ Transpolar Drift, Anticyclonic Drift, Cyclonic Drift and Double Gyre Drift. These four types account for 81% of the total, and reveal distinct seasonal variations. The Cyclonic Drift with a large-scale anticlockwise ice motion pattern trends to prevail in summer while the Anticyclonic Drift with an opposite pattern trends to prevail in winter and spring. The prevailing seasons for the Beaufort Gyre+Transpolar Drift are spring and autumn, while the Double Gyre Drift trends to prevail in winter, especially in February. The annual occurring times of the Anticyclonic Drift and the Cyclonic Drift are closely correlated with the yearly mean Arctic Oscillation (AO) index, with a correlation coefficient of -0.54 and 0.54 (both significant with the confident level of 99%), respectively. When the AO index stays in a high positive (negative) condition, the sea-ice motion in the Arctic Ocean demonstrates a more anticlockwise (clockwise) drifting pattern as a whole. When the AO index stays in a neutral condition, the sea-ice motion becomes much more complicated and more transitional types trend to take place.

Dynamics of future seasonal temperature trends and extremes in Europe: a multi-model analysis from CMIP3

European surface temperatures have increased during the past decades. According to climate projections, this warming is expected to continue in future years under enhanced radiative forcings. In addition to the mean increase, changes in temperature variability are likely to occur, with more frequent extreme seasons such as those recently observed in the past decade (e.g. summer 2003, autumn 2006). Yet, most of the processes driving such long-term tendencies remain unidentified and unexplored. A particularly important issue is how changes in the atmospheric dynamics over the North-Atlantic and Europe (NAE) contribute to trends in both mean and extreme temperatures. The high occurrence of the positive phase of the North Atlantic Oscillation (NAO) in the 1980s–1990s suggested that the European warming could result from a re-organization in the main structures of the NAE dynamics. However, the 2000s have rather revealed an inconsistency between atmospheric circulation conditions and European temperatures. Here we investigate the relationship between sea-level pressure (SLP) and 2-m temperature (T2m) using a flow-analogues method applied over both observations and future projections. We use 13 models of the Third phase of the Coupled Model Intercomparison Project (CMIP3) over 1961–2000, 2046–2065 and 2081–2100, from which we extract seasonal subensembles with respect to their representation of observed SLP-T2m seasonal relationships. First we show that the distribution of SLP does not undergo major changes in future climate according to these seasonal model-ensembles, albeit a general decline of the variability is observed for all seasons. Then, using the flow-analogues, we conclude that the projected European warming appears disconnected from changes in the NAE dynamics. Only in winter a slight shift towards positive NAO conditions could partially contribute to the future temperature increase. Finally, a focus over unusually warm/cold seasons reveals that future temperature extremes should likely to be associated with similar atmospheric circulations as observed during recent ones.

Different characteristics of cold day and cold surge frequency over East Asia in a global warming situation

[1] This study investigates the changes in winter cold extreme events over East Asia in the present and future climates. Two distinct terms to indicate cold extreme events are analyzed: “cold day,” which describes a temperature below a certain threshold value (e.g., simply cold weather), and “cold surge,” which describes an abrupt temperature drop (e.g., relatively colder weather than a previous day). We analyze both observations and long-term climate simulations from 13 atmospheric and oceanic coupled global climate models (CGCMs). The geographical distribution of sea level pressure corresponding to a cold day (cold surge) is represented by a dipole (wave train) feature. Although cold day and cold surge show similar patterns of surface air temperature, they are induced by the out-of-phase sea level pressures. From the results of our analysis of a series of future projections for the mid and late twenty-first century using the 13 CGCMs, cold day occurrences clearly decrease with an increasing mean temperature (a correlation coefficient of −0.49), but the correlation between cold surge occurrences and the mean temperature is insignificant (a correlation coefficient of 0.08), which is supported by the same results in recent observation periods (1980–2006). Thus, it is anticipated that cold surge occurrences will remain frequent even in future warmer climate. This deduction is based on the future projections in which the change in the day-to-day temperature variability is insignificant, although the mean temperature shows significant increase. The present results suggest that living things in the future, having acclimatized to a warmer climate, would suffer the strong impact of cold surges, and hence the issue of vulnerability to cold surges should be treated seriously in the future.

Simulated pre-industrial climate in Bergen Climate Model (version 2): model description and large-scale circulation features

Abstract. The Bergen Climate Model (BCM) is a fully-coupled atmosphere-ocean-sea-ice model that provides state-of-the-art computer simulations of the Earth's past, present, and future climate. Here, a pre-industrial multi-century simulation with an updated version of BCM is described and compared to observational data. The model is run without any form of flux adjustments and is stable for several centuries. The simulated climate reproduces the general large-scale circulation in the atmosphere reasonably well, except for a positive bias in the high latitude sea level pressure distribution. Also, by introducing an updated turbulence scheme in the atmosphere model a persistent cold bias has been eliminated. For the ocean part, the model drifts in sea surface temperatures and salinities are considerably reduced compared to earlier versions of BCM. Improved conservation properties in the ocean model have contributed to this. Furthermore, by choosing a reference pressure at 2000 m and including thermobaric effects in the ocean model, a more realistic meridional overturning circulation is simulated in the Atlantic Ocean. The simulated sea-ice extent in the Northern Hemisphere is in general agreement with observational data except for summer where the extent is somewhat underestimated. In the Southern Hemisphere, large negative biases are found in the simulated sea-ice extent. This is partly related to problems with the mixed layer parametrization, causing the mixed layer in the Southern Ocean to be too deep, which in turn makes it hard to maintain a realistic sea-ice cover here. However, despite some problematic issues, the pre-industrial control simulation presented here should still be appropriate for climate change studies requiring multi-century simulations.

Outflow of Arctic Ocean Sea Ice into the Greenland and Barents Seas: 1979–2007

Abstract Twenty-nine years of Arctic sea ice outflow into the Greenland and Barents Seas are summarized. Outflow is computed at three passages: Fram Strait, between Svalbard and Franz Josef Land (S–FJL), and between Franz Josef Land and Severnaya Zemlya (FJL–SZ). Ice drift at the flux gates has been reprocessed using a consistent and updated time series of passive microwave brightness temperature and ice concentration (IC) fields. Over the record, the mean annual area outflow at the Fram Strait is 706(113) × 103 km2; it was highest in 1994/95 (1002 × 103 km2) when the North Atlantic Oscillation (NAO) index was near its 29-yr peak. The strength of the “Transpolar Drift Stream” (TDS) was high during the late 1980s through the mid-1990s. There is no statistically significant trend in the Fram Strait area flux. Even though there is a positive trend in the gradient of cross-strait sea level pressure, the outflow has not increased because of a negative trend in IC. Seasonally, the area outflow during recent summers (in 2005 and 2007) has been higher (> 2σ from the mean) than average, contributing to the decline of summer ice coverage. Without updated ice thickness estimates, the best estimate of mean annual volume flux (between 1991 and 1999) stands at ∼2200 km3 yr−1 (∼0.07 Sv: Sv ≡ 106 m3 s−1). Net annual outflow at the S–FJL passage is 37(39) × 103 km2; the large outflow of multiyear ice in 2002–03, marked by an area and volume outflow of 141 × 103 km2 and ∼300 km3, was unusual over the record. At the FJL–SZ passage, there is a mean annual inflow of 103(93) × 103 km2 of seasonal ice into the Arctic. While the recent pattern of winter Arctic circulation and sea level pressure (SLP) has nearly reverted to its conditions typical of the 1980s, the summer has not. Compared to the 1980s, the recent summer SLP distributions show much lower SLPs (2–3 hPa) over much of the Arctic. Overall, there is a strengthening of the summer TDS. Examination of the exchanges between the Pacific and Atlantic sectors shows a long-term trend that favors the summer advection of sea ice toward the Atlantic associated with a shift in the mean summer circulation patterns.

Antarctic Sea-ice velocity as derived from SSM/I imagery

AbstractSea-ice velocities derived from remotely Sensed microwave imagery of the Special Sensor Microwave/Imager (SSM/I) have been analyzed for changes over time in Antarctic Sea-ice velocity, for the period 1988–2004. Year-to-year variability in mean Antarctic annual SSM/I-derived ice Speed is Small (17 year Standard deviation (SD) = 0.008 ms–1), with greater interannual variability in the zonal (eastward positive) velocity components (17 year SD = 0.016ms–1). Seasonally, minimum ice Speed is encountered during Summer, when nearly all Antarctic Sea ice is within the marginal ice zone. Ice motion peaks during winter and Spring, due to high velocities encountered in the outer pack of the Seasonal Sea-ice zone. The correlation (R2= 0.47) between winter Southern Annular Mode (SAM) and mean winter ice Speed highlights the importance of atmospheric forcing on Sea-ice dynamics. The Spatial pattern of the correlation of the Standardized SAM index with the June–November ice Speed exhibits a wave-3 pattern, which matches the Sea-level pressure distribution. Sea-ice Speed in the upstream regions of quasi-stationary centres of low Sea-level pressure is likely to increase (decrease) during high (low) SAMyears, and the opposite for Sea-ice Speed in the downstream regions of the centres.

Impact of the Advanced Microwave Sounding Unit Measurements on Hurricane Prediction

Abstract Due to the lack of meteorological observations over the tropical oceans, almost all the current hurricane models require bogusing of a vortex into the large-scale analysis of the model initial state. In this study, an algorithm to construct hurricane vortices is developed using the Advanced Microwave Sounding Unit (AMSU-A) data. Under rain-free atmospheric conditions, the temperature profile could be retrieved with a root-mean-square error of 1.5°C. Under heavy rainfall conditions, measurements from channels 3–5 are removed in retrieving temperatures. An application of this algorithm to Hurricane Bonnie (1998) shows well the warm-core eye and strong thermal gradients across the eyewall. The rotational and divergent winds are obtained by solving the nonlinear balance and omega equations using the large-scale analysis as the lateral boundary conditions. In doing so, the sea level pressure distribution is empirically specified, and the geopotential heights are calculated from the retrieved temperatu...

Recent changes in Arctic Ocean sea ice motion associated with the North Atlantic Oscillation

Examination of a new ice motion dataset of the Arctic Ocean over a recent eighteen year period (1978–1996) reveals patterns of variability that can be linked directly to the North Atlantic Oscillation. The intensity of the Icelandic Low, one of its centers of action, modulates the sea level pressure distribution over a broad region of the Arctic Ocean and the Greenland‐Iceland‐Norwegian and Barents Seas. Over the winters of 1988 through 1995, the Oscillation has remained in its positive phase contributing to coherent large‐scale changes in the intensity and character of ice transport in the Arctic Ocean. The significant changes include: the weakening of the Beaufort Gyre; the increase in ice export through the Fram Strait; the increase in ice import from the Barents/Kara Seas; the enhanced eastward transport of sea ice from the Laptev Sea; the weakening of the Transpolar Drift Stream; and, the reduction in ice extent in the Nordic Seas. All of these changes affect the regional and total sea ice mass balance of the Arctic Ocean.

The association between the north Indian Ocean and summer monsoon rainfall over India

Utilizing the marine meteorological data of the period 1961-81, the sea level pressure (SLP) and sea surface temperature (SST) distributions have been obtained on a 5° grid-mesh over the north Indian Ocean area bounded by 0°- 25°N, 50°- l00°E for each individual year. It has been found that the SLP and SST fields for the month of May provide predictive indications of subsequent summer monsoon rainfall over India. Significant negative correlations have been found between the mean SLPs of May over the latitudinal belts 5°-10°, 10°- 15°, 15°-20° and 20°-25°N of Arabian Sea and Bay of Bengal and all India rainfall departures of succeeding summer monsoon season. The mean SST gradient over the Arabian Sea between 7.5°- 17 .5°N during May has been found to have significant positive correlation with all India rainfall of subsequent monsoon. The study suggests that certain functions of SLP and SST of May over the north Indian Ocean can prove to be useful predictors for subsequent summer monsoon rainfall over India.