Variations In Outgoing Longwave Radiation Research Articles

Pre-earthquake Atmospheric and Ionospheric Anomalies before Taiwan Earthquakes (M 6.1 and M 6.4) on February (4th and 6th), 2018

Satellite measurements are becoming popular among the scientific community to identify earthquake precursors since its spatial coverage is more and round the clock measurements are possible. In this paper, we analyzed Total Electron Content (TEC), Outgoing Longwave Radiation (OLR), Sea Level Pressure (SLP), Surface Latent Heat flux (SLHF) and Sea Surface Temperature(SST) to identify any abnormal anomalies before Taiwan earthquakes which occurred on 4th February 2018 (M = 6.1, depth = 12 km) and 6th February 2018 (M = 6.4, depth = 17 km). The GPS data of International GNSS Service(IGS) stations (TWTF and CKSV) which operated 90 and 200 km away from the epicenter of the earthquake on 6th February 2018 respectively, were used for calculation of VTEC. The locations of these stations are within the preparatory zone of these earthquakes. The global parameters such as Dst, Kp, and IMF are also analyzed for the corresponding period of VTEC. We noticed the raise of temporal variations of 5–8 TECU before few days of the present earthquakes. The VTEC and other parameters such as SLP, SST, SLHF, and OLR were analyzed using the “Sliding Interquartile range method” during the period of 09th Jan to 10th Feb 2018 (33 days) to identify the abnormal signal due to these earthquakes. Strong positive anomalies occurred one day before the earthquake of 4th February and 1st, 3rd and 5th day before the Taiwan earthquake of 6th February 2018 with strong anomalous nature with an absolute amplitude of 5–8 TECU.The Cross wavelet analysis between Kp and TEC is carried out to study the impact of global geomagnetic activity on TEC during the seismic event and we found a negligible influence of global geomagnetic activity. The good raise of SLP on the day of the earthquake on 6th February 2018 have been noticed with the raise of 300 mb, the SLHF anomalies are observed at the interface of the earth’s surface and atmosphere. Moreover, anomalous variations in air temperature and OLR were observed 2 days before the occurrence of the earthquake on 6th February 2018. Well co-ordinated scrutiny of various parameters such as TEC, SLHF, and OLR indicates that they can be used as promising precursors to the impending devastating earthquakes with reasonable accuracy.

Satellite monitoring for Outgoing Longwave Radiation and Water Vapor during 2003 - 2016 in Iraq

This study explored the use of satellite data to monitor Outgoing Longwave Radiation (OLR) and Water Vapor (H2O) in Iraq. The retrieved monthly data obtained from Atmospheric Infrared Sounder (AIRS), included on the EOS Aqua satellite, from January 2003 to December 2016 are employed. In order to better assess these two parameters distribution, the spatiotemporal and long term trends analysis are provided for five stations dispersed across Iraq; Mosul, Sulaimaniyah, Rutba, Baghdad and Basra. The OLR and H2O monthly distribution shows important spatiotemporal variations values over study area, with a maximum in summer and minimum in winter. The higher OLR values of monthly average for study period occurred (370, 364) w/m2 in July and August at Rutba, and the lowest values of monthly average occurred were (232 w/m2) in January over Mosul and Sulaimaniyah. The higher H2O values (6.34 g/kg) observed in July and August over Baghdad and the lowest values of monthly average was (3.30 g/kg) in January and December over Mosul and Rutba. The long term trends analysis reveals decreasing trend in surface-OLR (0.0022 to 0.0026) w/m2 per year. The H2O vapor trend analyses have positive trend ranged from (0.005 to 0.015) g/kg per year. The satellite observation efficiently shows the spatial and temporal variations of OLR and H2O. This study sheds new light on the processes and analysis of both parameters emission over Iraq.

Contributing Factors to Spatiotemporal Variations of Outgoing Longwave Radiation (OLR) in the Tropics

Abstract Factors governing spatiotemporal variations of the daily outgoing longwave radiation (OLR) are studied using 35-yr (1979–2013) data records by employing multiple linear regression, wavelet transforms, and bandpass filtering methods. From the regression coefficients of nine predictors and the explained variances, we found that the largest contributions to OLR variability are associated with the Madden–Julian oscillation and El Niño–Southern Oscillation (ENSO). The ENSO signatures on OLR show dipole patterns over the Maritime Continent (MC) and Pacific regions with an extension to the Atlantic. Subsequently, the third significant contribution of the Indian Ocean dipole is confined to the Indian Ocean and Africa. Then, the solar cycle and stratospheric aerosols show mainly negative correlations, while a positive linear trend is observed mainly in the Northern Hemisphere. Lastly, factors associated with the stratospheric quasi-biennial oscillation (QBO) are the least significant contributor to OLR. In terms of oscillatory signals, time–longitude variations of the annual cycle (AC) show pairs of contrasting phases that characterize monsoon systems, in which the MC and Pacific regions are found to be in the same phase group. The most consistent AC signals are found to correspond with North and South American monsoons that respectively exhibit weakening and strengthening trends. Wavelet spectra and filtered OLR signals in intraseasonal oscillation, QBO, and ENSO frequency bands show an interdependent relationship that largely varies with time scale and longitudes.

Spatial and Temporal Distributions of Outgoing Longwave Radiation over Iraq: 2007 – 2016

The Outgoing Longwave Radiation (OLR), represents the total radiation emitted to the space by earth atmosphere system, is a critical component of the Earth’s radiation budget. Observations of OLR retrieved from Atmospheric Infrared Sounder (AIRS) on the EOS/Aqua platform during 2007-2016 show a strong, plume-like enhancement of OLR over central and southern-west parts of Iraq during June - September. Maximum values occurred in the southern region (365.27 watt/m2), were attributed to the hot, geographic nature and long sunny days. A greater draws down of the OLR occurred over pristine mountains environment at northern region in February (220.37 watt/m2). The monthly analysis shows the seasonal variations in the OLR values fluctuated between wet and dry seasons. The OLR value in dry season was higher than its values in wet season, and the mean standard deviation was (294.5 + 78.5 Watt/m2) over considered stations; Baghdad, Mosul, Rutba, Nasiriya and Basra for study period. The reductions of OLR values at northern area above latitude 34°, especially at mountains, through the study period due low emissivity and moist ground (low temperatures), and more cloudy sky days. Seasonal of OLR distributions shows variations in its values with high in summer, low in winter, and moderate in spring and autumn. The industrial and residential areas showed high OLR value, and low at rural and vegetated areas. The AIRS observation efficiently shows the spatial and temporal variations of OLR for the considered study area. This study sheds new light on the processes and analysis of the OLR emission over Iraq.

Observation of surface and atmospheric parameters using “NOAA 18” satellite: a study on earthquakes of Sumatra and Nicobar Is regions for the year 2014 (M ≥ 6.0)

Analysing pre-earthquake signals using satellite technology are getting importance among the scientific community, since round-the-clock survey for the wider region is possible compared to ground-based monitoring techniques. Several scientists are involved in various satellites and ground-based technologies to decode the complex physical mechanism of the earthquake process since 1980. They involved in measuring anomalous variations using space-based methodologies like EM signals, SAR interferometry, GPS for ionospheric sounding, satellite gravimetry, atmospheric sounding, Outgoing Longwave Radiation (OLR), radon gas and seismo-tectonic clouds. In this paper, the authors have considered surface latent heat flux (SLHF) and OLR satellite data for detailed analysis of earthquakes took place during the year 2014 in Sumatra and Nicobar Is regions. At the surface and atmospheric interface, the anomalous variations in SLHF were observed prior to the occurrence of the earthquake. Similarly, anomalous variations in OLR have been observed 3–30 days prior to the big earthquakes and it is measured above the cloud level. From the analysis, the author has found that variations in the SLHF and OLR flux can be utilized as efficient tools to identify the impending big earthquakes. SLHF and OLR variation level can give us a clue about the probable magnitude of earthquakes and also about earthquake preparation zones. Hence, by correlating the above-mentioned parameters, it is potential to key out the impending earthquakes with reasonable accuracy.

Diurnal variations of outgoing long wave radiation (OLR) vis a vis 4 January, 2016 Manipur earthquake (Mw: 6.7): An earthquake precursor?

Daily and diurnal variations of OLR from INSAT 3D and Kalpana satellites have been studied during 25 December, 2015 to 5 January, 2016 over the epicentral region of the Manipur earthquake of 4 January, 2016 (Mw 6.7) and other regions within the view of these satellites. The surface temperatures recorded at Imphal around 30 km from epicentre of this earthquake were also examined. It is found that OLR remained low prior to the occurrence of Manipur earthquake while much larger rise occurred over several other regions where no significant seismic activity was reported. The results corroborate inferences reported in earlier studies that OLR or temperature changes are related to meteorological causes and its sole identification as earthquake precursor may be misleading due to poor constraints.

Observation of pre-earthquake thermal signatures using geostationary satellites: implications for earthquake forecasting

For the past several decades, scientists have been exploring the possibilities of decoding the complex physical mechanism of the earthquake process using satellites and ground-based technologies. In recent years, use of satellite-based technologies has been preferred, since monitoring a broader region and round-the-clock surveillance is possible using geostationary satellites. Using sensors mounted on satellites, it is possible to observe anomalous thermal variations in both the atmosphere and the ground. Measurement of anomalous variations in outgoing longwave radiation (OLR) is one such technology used to identify earthquake preparation zones. Anomalous variations in OLR have been observed in the vicinity of the epicenter, 3 to 30 days prior to impending earthquakes. We have analyzed the OLR scenario for earthquakes with magnitude greater than 7.0 that occurred during April 2016. Analysis has been done to find the relationship between OLR flux variations and the magnitude of the earthquakes. From the analysis, we have found that the recurrence frequency of OLR anomaly and cumulative energy flux of OLR can give us vital clues about the probable magnitude of impending earthquakes.

Variability of Madden Julian Oscillations (MJO) observed over southern India using radiosonde observations

In the present work, characteristics of 30–50 day oscillations (referred to as the MJO) in tropospheric and lower stratospheric wind and temperature have been studied using long-term high resolution radiosonde observations at a tropical station, Gadanki (13.5°N, 79.2°E) for the period 2006–2012. Wind and temperature perturbations showed clear features of the MJO with higher amplitudes between 10 and 18km altitude. Interestingly, the MJO signal is confined vertically to different altitudes in different seasons. Variability in the perturbations of wind and temperature similar to that of outgoing long-wave radiation (OLR) with a few cases showing an out of phase relation. The amplitudes of these oscillations are larger in the winter and pre-monsoon seasons than in the monsoon season where the largest amplitudes are confined below the Tropical Easterly Jet (~16km). There also exists a large inter-annual variability in the MJO. Spatio-temporal variability of OLR not only showed the features of the MJO but also northward and eastward propagation in the monsoons and winter seasons, respectively, in a few cases. It is found that convection leads the MJO in the zonal wind by 8–12 days in all the seasons except in winter. One intriguing result observed is the vitiation of the MJO pattern by the presence of strong wind shears during monsoon season. We expect this study would be helpful in representing the MJO features in the vertical in the general circulation models (GCMs) which is still a major challenge.

The Walker circulation, diabatic heating, and outgoing longwave radiation

AbstractFor the tropical atmosphere on planetary scales, it is common to model the circulation using strong damping. Here with new data analysis techniques, evidence suggests that damping can actually be neglected. Specifically, near the equator, the east‐west overturning circulation is in agreement with the undamped wave response to atmospheric heating. To estimate the heating, satellite observations of outgoing longwave radiation (OLR) are used. Frequently, OLR is used as a heuristic indicator of cloudiness. Here the results further suggest that OLR variations are actually proportional to diabatic heating variations, with a proportionality constant of 18 W m−2 (K d−1)−1. While the agreement holds best over long time averages of years or decades, it also holds over shorter periods of one season or 1 month. Consequently, it is suggested that the strength of the Walker circulation—and its evolution in time—could be estimated using satellite data.

A Modified Multivariate Madden–Julian Oscillation Index Using Velocity Potential

Abstract A new Madden–Julian oscillation (MJO) index is developed from a combined empirical orthogonal function (EOF) analysis of meridionally averaged 200-hPa velocity potential (VP200), 200-hPa zonal wind (U200), and 850-hPa zonal wind (U850). Like the Wheeler–Hendon Real-time Multivariate MJO (RMM) index, which was developed in the same way except using outgoing longwave radiation (OLR) data instead of VP200, daily data are projected onto the leading pair of EOFs to produce the two-component index. This new index is called the velocity potential MJO (VPM) indices and its properties are quantitatively compared to RMM. Compared to the RMM index, the VPM index detects larger-amplitude MJO-associated signals during boreal summer. This includes a slightly stronger and more coherent modulation of Atlantic tropical cyclones. This result is attributed to the fact that velocity potential preferentially emphasizes the planetary-scale aspects of the divergent circulation, thereby spreading the convectively driven component of the MJO’s signal across the entire globe. VP200 thus deemphasizes the convective signal of the MJO over the Indian Ocean warm pool, where the OLR variability associated with the MJO is concentrated, and enhances the signal over the relatively drier longitudes of the equatorial Pacific and Atlantic. This work provides a useful framework for systematic analysis of the strengths and weaknesses of different MJO indices.

On the Longwave Climate Feedbacks

Abstract This paper mainly addresses two issues that concern the longwave climate feedbacks. First, it is recognized that the radiative forcing of greenhouse gases, as measured by their impact on the outgoing longwave radiation (OLR), may vary across different climate models even when the concentrations of these gases are identically prescribed. This forcing variation contributes to the discrepancy in these models' projections of surface warming. A method is proposed to account for this effect in diagnosing the sensitivity and feedbacks in the models. Second, it is shown that the stratosphere is an important factor that affects the OLR in transient climate change. Stratospheric water vapor and temperature changes may both act as a positive feedback mechanism during global warming and cannot be fully accounted as a “stratospheric adjustment” of radiative forcing. Neglecting these two issues may cause a bias in the longwave cloud feedback diagnosed as a residual term in the decomposition of OLR variations. There is no consensus among the climate models on the sign of the longwave cloud feedback after accounting for both issues.

Ionospheric disturbances with the time of occurrence, magnitude and location of the earthquake (M6.5) near the Indian subcontinent

The present study purports the analysis of total electron content (TEC, which is one of the major ionosphere anomalies during the earthquake), sea surface temperature (SST) and outgoing long-wave radiation (OLR) during the earthquake event recorded on 10 March 2013 (M = 6.5). Global assimilative ionosphere modelled output TEC values have been used for this present study; the clear signature of TEC during the recorded earthquake has been noticed (i.e. increase in TEC 60–70 TECU during the event). The correlation between the magnitude and location of earthquake with TEC is around 0.9, and the least correlation between SST and OLR is due to concerned atmospheric effects; we tried to study the variations of SST and OLR prior during and after the event from Kalpana satellite image products archived by IMD.

A comparative analysis of intraseasonal atmospheric variability in OLR and 1DD GPCP rainfall data over Central Africa

The spatial and temporal structures of the leading modes of intraseasonal atmospheric variability over Central Africa using outgoing longwave radiation (OLR) and one-degree daily Global Precipitation Climatology Project (1DD GPCP) data are compared. A spectral analysis indicates that in the two datasets, the intraseasonal variability is dominated by 20–70-day period bands with center near 40–50 days. Results from empirical orthogonal function (EOF) analysis have shown that three main spatial structures characterize the leading modes of 20–70-day intraseasonal oscillations (ISO), but they differ in the two data by the amount of variance explained by each mode. For both time series, the power spectra of all the three principal components peak around 40–50 days, indicating Madden–Julian oscillation (MJO) signal. Moreover, the cross correlation computed among the principal components indicates that there exists a relatively high positive correlation between the EOFs of similar spatial loadings. For the two datasets, an index of MJO strength was built by averaging the 30–50-day power for each day and each EOF mode. A plot of the two indices revealed a coherent onset, peak, and decay of ISO activity but with different amplitudes. The correlation coefficients computed between the ISO indices corresponding to each mode revealed that they are highly correlated, especially for the annual mean time series where the correlation coefficient reaches up to 0.88 for the Tanzanian mode. Overall, the analysis showed that the leading modes are similar, but the 1DD GPCP loadings have better spatial localization, when compared with those of OLR datasets.

Investigating Variability of Outgoing Longwave Radiation over Peninsular Malaysia Using Wavelet Transform

Abstract The present study analyzes and quantifies the spatial–temporal variability of outgoing longwave radiation (OLR) over peninsular Malaysia using the continuous wavelet transform (CWT) from 2003 to 2010. The goal is to understand the long-term variability of OLR over Malaysia in terms of time–frequency variations in relation to the monsoon period and other weather phenomena. The study regions selected were the west coast, east coast, and southern part of peninsular Malaysia. The OLR variation characteristics in time and space derived from wavelet transform were found to be distinctly different in these three regions. In these three regions, OLR showed significant periodicities dominated by the annual cycle, followed by a semiannual cycle. The west coast of peninsular Malaysia has a lower annual component compared to the other regions because of the rain-sheltering effect by the mountain range that blocked the heavy rainfall from northeast monsoon winds. Besides that, the results show that the wet and dry spells coincide with local monsoon and intermonsoon periods. Meanwhile, the results also revealed that the semiannual variation is statistically significant during 2004–06. The strong semiannual variation is coincident with several droughts that resulted from the strong El Niño events in 2004–06. In addition, the phase plot of wavelet coefficients shows that the variations at various scales are in phase, which coincided with the sudden variations of OLR, indicating heavy flood occurrences in the southern part of peninsular Malaysia. The results show that CWT is a powerful tool for analysis of phenomena involving multiscale interactions that exhibit localization in both time and frequency.

Impact of Sun-Synchronous Diurnal Sampling on Tropical TOA Flux Interannual Variability and Trends

AbstractSatellite observations of the earth’s radiation budget (ERB) are a critical component of the climate observing system. Recent observations have been made from sun-synchronous orbits, which provide excellent spatial coverage with global measurements twice daily but do not resolve the full diurnal cycle. Previous investigations show that significant errors can occur in time-averaged energy budgets from sun-synchronous orbits if diurnal variations are ignored. However, the impact of incomplete diurnal sampling on top-of-atmosphere (TOA) flux variability and trends has received less attention. A total of 68 months of 3-hourly tropical outgoing longwave radiation (OLR) and reflected shortwave radiation (RSW) fluxes from the Clouds and the Earth’s Radiant Energy System (CERES) synoptic (SYN) data product is used to examine the impact of incomplete diurnal sampling on TOA flux variability. Tropical OLR and RSW interannual variability and trends derived from sun-synchronous time sampling consistent with the Terra satellite from 2000 to 2005 show no statistically significant differences at the 95% confidence level with those obtained at 3-hourly time sampling at both 1° × 1° and 10° × 10° regional scales, as well as for tropical means. Monthly, 3-hourly OLR composite anomalies are decomposed into diurnally uniform and diurnal cycle shape change contributions to explain the impact of sampling on observed TOA flux variability. Diurnally uniform contributions to OLR variability account for more than 80% of interannual OLR variability at 1° × 1° spatial scales. Diurnal cycle shape variations are most important in equatorial land regions, contributing up to 50% to OLR variability over Africa. At spatial scales of 10° × 10° or larger, OLR variance contributions from diurnal cycle shape changes remain smaller than 20%.

Variability of Monthly Diurnal Cycle Composites of TOA Radiative Fluxes in the Tropics

Abstract Earth system variability is generated by a number of different sources and time scales. Understanding sources of atmospheric variability is critical to reducing the uncertainty in climate models and to understanding the impacts of sampling on observational datasets. The diurnal cycle is a fundamental variability evident in many geophysical variables—including top-of-the-atmosphere (TOA) radiative fluxes. This study considers aspects of the TOA flux diurnal cycle not previously analyzed: namely, deseasonalized variations in the monthly diurnal cycle composites, termed monthly diurnal cycle variability. Significant variability in the monthly diurnal cycle composites is found in both outgoing longwave radiation (OLR) and reflected shortwave (RSW). OLR and RSW monthly diurnal cycle variability exhibits a regional structure that follows traditional, climatological diurnal cycle categorization by prevailing cloud and surface types. The results attribute monthly TOA flux diurnal cycle variability to variations in the diurnal cloud evolution, which is sensitive to monthly atmospheric dynamic- and thermodynamic-state anomalies. The results also suggest that monthly diurnal cycle variability can amplify or buffer monthly TOA flux anomalies, depending on the region. Considering the impact of monthly diurnal cycle variability on monthly TOA flux anomalies, the results suggest that monthly TOA flux diurnal cycle variability must be considered when constructing a TOA flux dataset from sun-synchronous orbit. The magnitude of monthly diurnal composite variability in OLR and RSW is regionally dependent—1–7 W m−2 and 10%–80% relative to interannual TOA flux variability. The largest (4–7 W m−2; 40%–80%) and smallest (1–3 W m−2; 10%–30%) TOA flux uncertainties occur in convective and nonconvective regions, respectively, over both land and ocean.

Mechanisms of ozone enhancement during stratospheric intrusion coupled with convection over upper troposphere equatorial Africa

The possible cause and sources of enhanced ozone at upper tropospheric equatorial Africa, observed by cruise Measurements of OZone by Airbus In Service Aircraft (MOZAIC) during the Northern Hemisphere winter in 1996 and 1997 on flight routes from Johannesburg to Vienna, are investigated. Two enhanced ozone events over upper tropospheric equatorial Africa are identified from MOZAIC observations on April 6, 1996 and March 27, 1997. High resolution ECMWF reanalysis GOME ozone has exhibited enhancement as well during these periods suggesting that the two events are not isolated small scale events but part of a larger scale process. As a result, the source and mechanisms of ozone increase over the region are further analysed using reanalysis data from ECMWF, outgoing long wave radiation (OLR) from NOAA and Meteosat images from NASA, International Satellite Cloud Climatology Project. Equivalent latitude computed from potential vorticity has shown that massive mid- and high-latitude stratospheric ozone rich airmass is funnelled into lower latitude troposphere through troughs extending from large amplitude planetary waves towards equator. The Space-time Fourier decomposition of meridionally averaged zonal wind has revealed that these planetary wave activities are linked to waves with zonal wavenumber 1–2, which prevail during Northern Hemisphere winter. Additional analysis to understand the mechanisms of ozone enhancement was made using Multitaper Method–Singular Value Decomposition (MTM–SVD) spectral approach. The analysis confirms that ozone enhancement over the region is dependent on the relative position of positive PV and direction of wind anomalies. The high relative humidity measured simultaneously with ozone onboard MOZAIC, Meteosat imageries and circulation during the events have shown presence of deep convection. The coherent variation of OLR and ozone found over 8-day temporal cycle determined from MTM–SVD has indicated existence of OLR negative forcing in the upper troposphere and positive forcing in the lower stratosphere. These results show coupling of PV intrusion and deep convection over continental equatorial Africa in the same manner as the climatologically preferred intrusion over mid-ocean in eastern pacific. Moreover, the results enrich previous understanding with purely observational high resolution MOZAIC and ERA-Interim datasets, and statistical method.

Tropical Outgoing Longwave Radiation and Longwave Cloud Forcing Diurnal Cycles from CERES

Abstract The diurnal cycle is a fundamental earth system variability driven by daily variations in solar insolation. Understanding diurnal variability is important for characterizing top-of-atmosphere and surface energy budgets. Climatological and seasonal first diurnal cycle harmonics of outgoing longwave radiation (OLR) and longwave cloud forcing (LWCF) are investigated using the Clouds and the Earth’s Radiant Energy System (CERES) synoptic 3-hourly data. A comparison with previous studies indicates generally similar results. However, the results indicate that the CERES OLR diurnal cycle amplitudes are 10%–20% larger in desert regions than previous analyses. This difference results from the temporal interpolation technique overestimating the daily maximum OLR. OLR diurnal cycle amplitudes in other tropical regions agree with previous work. Results show that the diurnal maximum and minimum OLR variability contributes equally to the total OLR variance over ocean; however, over land the diurnal maximum OLR variance contributes at least 50% more to the total OLR variability than the minimum OLR. The differences in maximum and minimum daily OLR variability are largely due to differences in surface temperature standard deviations at these times, about 5–6 and 3–4 K, respectively. The OLR variance at diurnal maximum and minimum is also influenced by negative and positive correlations, respectively, between LWCF and clear-sky OLR. The anticorrelation between LWCF and clear-sky OLR at diurnal OLR maximum indicates smaller cloud fractions at warmer surface temperatures. The relationship between LWCF and clear-sky OLR at diurnal minimum OLR appears to result from a preference for deep convection, more high clouds, and larger LWCF values to occur with warmer surface temperatures driving a narrower diurnal minimum OLR distribution.

Implications for the low latitude cloud formations from solar activity and the quasi-biennial oscillation

We examined the effect of the 11-year solar cycle and quasi-biennial oscillation (QBO) on the ∼27-day solar rotational period detected in tropical convective cloud activity. We analyzed the data of outgoing longwave radiation (OLR) for AD1979–2004, dividing into four different cases by the combination of high and low solar activities in terms of the 11-year variation, and easterly and westerly stratospheric winds associated with QBO. As a result, ∼27-day variation has been most significantly detected in high solar activity period around the Indo-Pacific Warm Pool. Based on correlation analysis, we find that solar rotation signal can explain 10–20% of OLR variability around the tropical warm pool region during the high solar activity period. The spatial distribution has been, however, apparently different according to the phases of QBO. It is suggested that the 11-year solar cycle and stratospheric QBO have a possibility to cause large-scale oceanic dipole phenomena.

Quasi-biennial oscillation signals in outgoing long-wave radiation of the equator

In the present paper, the authors use wavelet transform technique to study time-series of outgoing long-wave radiation (OLR) anomaly at the equator during 1979–2005. The results show that quasi-biennial oscillation (QBO) signals exist in the OLR variation and the QBO cycle has remarkable temporal variability in its amplitude and phase. The periodic length of the QBO fluctuation is about 2.2-year before 1986. After that time, the length mainly changes from about 2.4- to 2.6-year. Analyzing the anomaly data set of 850 MB trade wind index (TWI) at west Pacific during this period, we have found that the obvious time-variations characteristics of the QBO cycle also exist in the TWI change at west Pacific and are in good consistence with that of the OLR change. The quasi-biennial fluctuation of the TWI change can explain that of the OLR change to a large extent.