Michael S. Halpert

Quantifying Southern Oscillation-precipitation relationships

Abstract A series of earlier studies has identified regions of the world in which precipitation appears to have a consistent relationship with the Southern Oscillation (SO). In this paper, the authors attempt to quantify this relationship based on shifts in the statistical distribution of precipitation amounts with emphasis on shifts in the median, which are associated with the warm (low SO index) and cold (high SO index) phases of the SO. This paper is partially an attempt to provide long-range forecasters with some guidance in making seasonal and multiseasonal predictions. Observed SO-related shifts in the median precipitation amounts, expressed as percentiles with respect to “climatological” conditions, can he used as a simple indication of the “typical” SO response for a given region. In general, the authors find that for many of the large areas identified in previous studies, median precipitation amounts shift on the order of 20 percentile points, that is, from the median to either the 30th percentil...

Surface Temperature Patterns Associated with the Southern Oscillation

Abstract The “typical” global and large-scale regional temperature patterns associated with the low (warm) and high (cold) phases of the Southern Oscillation (SO) are investigated. A total of 12 separate regions were found to have consistent temperature patterns associated with low phase of the SO, while 11 areas were found to have temperature patterns associated with the high phase. Of these areas, 9 have expected temperature patterns during both phases of the SO. In the tropics, temperature anomalies are of the same sign as the SO-related sea surface temperature (SST) anomaly in all land regions except for one area in the west Pacific. Three extratropical responses to the low phase of the SO are found over North America and one is found in Japan. High SO-temperature patterns were found in the extratropies for Japan, western Europe, and northwestern North America. The identified temperature responses are more consistent in tropical regions than in the extratropies. The SO can influence the estimation of ...

Observed tropospheric biennial variability and its relationship to the southern oscillation

Abstract Tropospheric biennial variability in several components of the Southern Oscillation (SO) is defined and described through analysis of observational data from the Comprehensive Ocean-Atmosphere Data Set (COADS), as well as through investigation of several SO index time series. The analysis suggests that the temporal behavior of the SO can be described in terms of three components: 1) a pervasive biennial pulse, which appears to be strong in both the Indian Ocean and the west Pacific surface zonal winds as well as in several SO indices, 2) the annual cycle, which tends to set the phase of biennial variability for the major SO excursions, and 3) a low-frequency, or residual, variability, which may be associated with temporal scales between large SO episodes. This study also supports recent papers in suggesting that complete models of the SO must include the Indian Ocean basin.

Observing and Predicting the 2015/16 El Niño

AbstractThe El Nino of 2015/16 was among the strongest El Nino events observed since 1950 and took place almost two decades after the previous major event in 1997/98. Here, perspectives of the event are shared by scientists from three national meteorological or climate services that issue regular operational updates on the status and prediction of El Nino–Southern Oscillation (ENSO). Public advisories on the unfolding El Nino were issued in the first half of 2015. This was followed by significant growth in sea surface temperature (SST) anomalies, a peak during November 2015–January 2016, subsequent decay, and its demise during May 2016. The life cycle and magnitude of the 2015/16 El Nino was well predicted by most models used by national meteorological services, in contrast to the generally overexuberant model predictions made the previous year. The evolution of multiple atmospheric and oceanic measures demonstrates the rich complexity of ENSO, as a coupled ocean–atmosphere phenomenon with pronounced glob...

Modulation of Southern Oscillation-Northern Hemisphere Mid-Winter Climate Relationships by the QBO

Abstract A possible relationship between the phase of the Quasi-Biennial Oscillation (QBO) and the effect of the Southern Oscillation (SO) on the January-February climate in the Northern Hemisphere is examined. Findings suggest a preference for the tropical/Northern Hemisphere (TNH) circulation pattern in response to anomalies in the SO in east QBO phase years, and for the Pacific/North American (PNA) pattern in west QBO phase years. This extends previous findings relating the strength of the TNH pattern to tropical Pacific sea surface temperature during ENSO episodes. This differentiation has fairly clear-cut implications for the January-February United States surface temperature anomaly pattern when a low (high) SO episode is in progress. The TNH emphasizes warmth (cold) in the Great Lakes/western Midwest; whereas the PNA induces a generally higher amplitude pattern, emphasizing cold (warmth) in the Southeast and warmth (cold) in the western third of the country. The SO-climate relationships appear appr...

The day-to-day monitoring of the 2011 severe drought in China

Dry/wet condition has a large interannual variability. Decision-makers need to know the onset, duration, and intensity of drought, and require droughts be monitored at a daily to weekly scale. However, previous tools cannot monitor drought well at this short timescale. The Palmer Drought Severity Index has been found dissatisfactory in monitoring because of its complexity and numerous limitations. The Standardized Precipitation Index (SPI) always asks for a timescale, and precipitation is averaged over the period of the scale. Because of this, the SPI cannot be used for short scales, e.g., several days, and what it tells is the overall drought situation of the period. The weighted average of precipitation (WAP) developed by Lu (Geophys Res Lett 36:L12707, 2009) overcomes the deficiency of the SPI; it does not require a timescale, and can provide the drought (and flood) extent of each day. Therefore, the WAP can monitor drought at scales from daily to weekly, monthly, and any longer scale, and is really “flexible and versatile for all timescales”. In this study, the standardized WAP (SWAP) is used to monitor the 2011 drought over China. Drought swept the country during the year from north to south and from east to west. In spring, a once-in-a-fifty-year drought occurred over the Yangtze River basin and the southern region, causing serious shortage of drinking water for people and livestock, as well as tremendous losses in agriculture and the shipping industry. Results show that the SWAP, with its monthly mean plots, can well reproduce the seasonal shift of the 2011 drought across the country. The animation of daily plots demonstrates that the SWAP would have been able to monitor the day-to-day variation of the spring drought around the Yangtze River basin. It can provide the details of the drought, such as when the drought emerged over the region, how long it maintained there (though drought area may move back and forth with extension and contraction of the area), and when the drought relieved over the basin.

An Analysis of CPC’s Operational 0.5-Month Lead Seasonal Outlooks

AbstractAn analysis and verification of 15 years of Climate Prediction Center (CPC) operational seasonal surface temperature and precipitation climate outlooks over the United States is presented for the shortest and most commonly used lead time of 0.5 months. The analysis is intended to inform users of the characteristics and skill of the outlooks, and inform the forecast producers of specific biases or weaknesses to help guide development of improved forecast tools and procedures. The forecast assessments include both categorical and probabilistic verification diagnostics and their seasonalities, and encompass both temporal and spatial variations in forecast skill. A reliability analysis assesses the correspondence between the forecast probabilities and their corresponding observed relative frequencies. Attribution of skill to specific physical sources is discussed. ENSO and long-term trends are shown to be the two dominant sources of seasonal forecast skill. Higher average skill is found for temperatur...

1992 Brings return to moderate global temperatures

Natural events, such as the Mt. Pinatubo eruption in the Philippines and the El Nino/Southern Oscillation (ENSO) episode in the tropical Pacific Ocean, had major impacts on the global climate in 1992. These phenomena were associated with a return to more moderate global temperatures during 1992 after several years of record or near-record high temperatures. During the first part of the year, the 1991–1992 ENSO episode contributed to above normal temperatures in the Northern Hemisphere, while cooling during the latter part of the year was associated with the aerosol cloud produced by the June 1991 eruption of Mt. Pinatubo. By the spring of 1992, the stratospheric aerosol cloud had extended from the tropics well into both hemispheres. In this report, global surface temperature anomalies are defined as departures from the 1961–1990 base period means. As the aerosol cloud spread throughout the Northern Hemisphere during a time of increasing solar radiation, the surface temperature anomalies responded by becoming less positive over much of the hemisphere. This relative cooling helped to make 1992 the coolest year since 1986. Temperatures also were dramatically cooler throughout the troposphere.

Climate monitoring using an AVHRR-based vegetation index

Abstract A normalized difference vegetation index (NDVI) has been produced and archived on a 1° latitude by 1° longitude grid between 55° S and 75° N. There are many sources of data errors in the NDVI including cloud contamination, scan angle biases, changes in solar zenith angle, and sensor degradation. Week-to-week variability is primarily caused by cloud contamination and scan angle biases and can be minimized by temporally filtering the data. Orbital drift and sensor degradation introduces interannual variability into the dataset. These trends make the usefulness of a long-term climatology uncertain and limit the usefulness of the NDVI. Elimination of these problems should produce an index that can be used for climate monitoring.

The Global Climate of June–August 1991: Tropical Pacific Warm Episode Conditions Evolve; New Base Period Means Established

Tropical Pacific atmospheric and oceanic indices continued to indicate early stages of an ENSO episode. The increase in convection during August 1991 confirmed a continued development of the 1991-92 warm episode in the equatorial Pacific. Circulation anomalies, persistent in the Northern Hemisphere, were associated with well above normal surface temperatures and below normal precipitations. In the southern Hemisphere, the primary circulation anomaly, a blocking anticyclone, dissipated during July. 9 refs., 31 figs., 1 tab.