By Frank Bosse and Fritz Vahrenholt
In February 2016 our sun’s activity was, as in almost every month of the current cycle, well below the average. The observed SSN (SunSpotNumber) was 57.2. The average of the cycles 1 … 23 for this month is 80.8, thus the observed activity was 71% of the average value in the current 24th cycle.
Fig.1: The current activity of the cycle 24 (SC 24, red) compared to the average activity of the cycles 1 … 23 (blue) and cycle 5 (SC5, black).
A comparison of the cycles to each other:
Fig.2: The activity of the cycles 1 … 24. The values are generated with the addition of the monthly anomalies (the differences between the observed SSN values and the average value, as they are drawn in blue in Fig. 1)
In total only 57% of the SSN of the average cycle was observed during cycle 24. Most likely, the cycle will be one of the three weakest since observations began in 1749, and will be close to the Dalton Minima cycles (ca. 1790-1830, SC 5 … 7).
What is the likely continuation after the SC24? Previously (most recently here ) we indicated that the first clue for the nature of the next cycle is the strength of the polar fields of the Sun at the minimum of sunspot activity prior to the start of the cycle. Although we have not yet reached this point, we will nevertheless already take a preparatory look at these fields. We have processed the data that we obtained from here up to the end of February 2016. We used of the smoothed data (in the series with the “f” for low-pass filter) because the unfiltered data are too much affected by short-term variations.
Figure 3: The smoothed series of polar fields of the sun, the average (black) from the northern hemisphere (Nf, blue) and inverted southern hemisphere (-SF, red).
The polar fields of the sun oscillate out of phase with the spot cycle: at the maximum of these, the polar fields see a polarity reversal (zero crossing) and vice versa. Especially the fields of the NH grow significantly slower after the SSN Maximum in 2013 than measured after the reversals since the mid-70s. The SH (red in Figure 3), however, behaves quite normally and pushes the average (black in Figure 3) upwards.
The next figure looks at the differences between the two hemispheres:
Figure 4: The hemispherical differences of the polar fields of the sun. Positive values indicate stronger fields of NH, negative ones stronger fields of the SH.
It is obvious that different field strengths are not unusual. However, it should be noted that throughout the cycle since 2008 the fields of the SH were stronger than those of the NH (except during the reversal in 2013) and we currently record the largest difference in the fields since 1976, the beginning of the available data. Several papers deal with such a phenomenon, i.e. Munoz-Jaramillo et al. (2013) and Ashish Goe et al. (2007) . They link an asymmetry of the polar fields to a hemispheric decoupling of the solar dynamo. The latter paper also discusses the idea that a strong asymmetry of the solar dynamo might have been one of the causes of the Maunder Minimum (a period of very low solar activity 1715 to 1645). A closer look at the different field strengths of the polar fields therefore seems to make sense. We are curious of the behavior during the next one to two years, after this time the fields should already be at their maximum and the prediction of the next cycle should be quite possible.
Broken temperature records
The global temperature in February announced by GISS was 1.35 °C above the average from 1951 to 1980. This is an impressive record, 0.8 ° C (!) warmer than in February 2014. What is behind such a large jump in a relatively short time? One of the reasons is of course the current El Nino. Another element is the Indo-Pacific Warm Pool (IPWP). It extends from 90° East to 180° East and 20° South to 20° North:
Fig. 5: The IPWP (turquoise highlighted). Source: “Google Earth”
This sea area receives heated water of the tropical Pacific from South / Central America, driven by the trade winds under neutral conditions of ENSO (El Nino Southern Oscillation) and during La Nina situations. We explained it here in more detail. Largescale, the globally highest ocean temperatures occur in this IPWP area, about 28.5°C. The heat that comes from the entire tropical Pacific is stored down to 500m water depth. The following figure shows how temperatures in this depth range developed since 2004:
Fig. 6: The vertical temperature distribution of IPWP (dbar = m water depth). Figure base on “Argo Global Marine Atlas”.
Clearly recognizable: Small El Nino 2004/2005 (blue = cooler), the La Nina 2008 caused a warming of IPWP, the El Nino 2009/2010 cooled, the La Nina 2011-2012 brought back the heat. Since 2014 a marked cooling occurs over the entire depth interval. For the discussion of the current global heat pulse, we concentrate on the period after January 2013.
Fig. 7: The temperatures of IPWP to 500m water depth (blue) since 2013, and the history of global temperatures (GISS, red) respectively to December 2015. (Data: GISS, Argo)
The average temperature of the IPWP has decreased by about 1°C since spring of 2013. Since the beginning of the Argo measurements in 2004, it has never been cooler than today. Note that this refers to a huge water mass of about 16 million cubic kilometers. For comparison: The energy that has been released from here corresponds to the amount that the whole earth receives from the sun by the solar radiation flux during a 4 days period. This huge amount of energy increases the global surface temperature which leads to increased radiation of a good part of the heat into space. An El Nino in the end therefore generates a heat loss of the system earth. The current pulse of warming is partly a consequence of this natural process. The recent temperature records therefore are more related to the natural ENSO cycle than to global warming of probably about 0.01° C / year by the effect of moderate greenhouse gases, when allowing for a reduced CO2 climate sensitivity.