Home / Weather / At the 1998 Obvious Step-Up in UAH Land-minus-Ocean Decrease Tropospheric Temperatures

At the 1998 Obvious Step-Up in UAH Land-minus-Ocean Decrease Tropospheric Temperatures

Reposted from Dr Roy Spencer’s Weblog

November seventh, 2019 through Roy W. Spencer, Ph. D.

A follower of our UAH international decrease tropospheric temperature (LT) dataset named “JJ” emailed me asking about what could be thought to be a spurious function within the dataset.

The function is most simply noticed should you plot the per thirty days international time collection of Land-minus-Ocean (hereafter “L-O”) temperature anomalies. The end result turns out to turn a step-up of about zero.16 deg. C in Might of 1998.

Fig. 1. Distinction between the UAH decrease tropospheric (LT) land and ocean temperature anomalies between January 1979 and August 2019, appearing an obvious step-up within the distinction happening in Might 1998. The dashed traces display the common values earlier than and after that date, whilst the curve is a fifth order polynomial are compatible to the knowledge.

The yr 1998 is essential for our dataset as a result of this is when the primary (NOAA-15) Complex Microwave Sounding Unit (AMSU) got here on-line, which initiated the transition from the older Microwave Sounding Gadgets (MSU, the closing of which used to be at the NOAA-14 satellite tv for pc).

AMSU didn’t have precisely the similar channel frequency variety because the MSU, so the nominal layers of the ambience sensed had been somewhat other. Most significantly, the AMSU channel five has a weighting serve as that senses relatively extra of the skin and decrease troposphere than MSU channel 2. If one didn’t account for this truth, the AMSU’s better floor sensitivity would produce upper temperatures over land and decrease temperatures over the sea (after a global-average intercalibration between MSU and AMSU used to be carried out). [The reason why is that these channel frequencies are not sensitive to changes in sea surface temperature, because the microwave emissivity decreases as SST increases. The effect is small, but measurable.]

However since those are through-nadir scanners, every view attitude relative to the native vertical measures a somewhat other layer anyway, which permits us to compare the AMSU and MSU measurements. Once we advanced Model 6 of the dataset, we discovered that the 50-60 GHz oxygen absorption concept used to search out the view attitude from AMSU5 that perfect fits MSU2, the ensuing temperature anomalies over land had been nonetheless too heat relative to the oceans. This intended that we needed to carry out an empirical (data-dependent) somewhat than theoretical matching of the AMSU and MSU view angles.

The best way we gauged the fit between MSU and AMSU is how the temperature anomaly patterns transition throughout coastlines: we required that there must be little discernible trade in that development. Sooner than our optimized matching, the land anomalies had been noticeable hotter than the sea anomalies as options crossed coastlines. However after optimization in our Model 6 dataset, right here’s the LT anomaly map for closing month (October 2019), which presentations no proof for land-vs-ocean artifacts.

UAH-global-LT-land-minus-ocean-2

Fig. 2. October 2019 LT temperature anomalies relative to the 1981-2010 common annual cycle. Observe the anomalies have a easy transition between land and ocean, as can be anticipated for deep-layer tropospheric temperatures (however no longer essentially floor temperatures).

However, changes like those are by no means highest. So, the query stays: Is there a spurious trade within the L-O temperature distinction happening in 1998?

Proof that the L-O trade in 1998 is actual

There are a couple of traces of proof that counsel the Might 1998 step-up in L-O temperatures is actual.

First, if the impact used to be because of the advent of AMSU in 1998, it will have befell in August, no longer in Might (Three months earler). Additionally, the impact must were slow since for nearly four years after August 1998 the LT dataset is part MSU (NOAA-14) and part AMSU (NOAA-15), and then it becaume 100% AMSU.

However a extra vital piece of proof is the impact of El Nino and L. a. Nina on L-O. Right through El Nino, the sea airmasses heat greater than the land airmasses (particularly within the tropics), in order that L-O has a tendency to be extra detrimental. Up till the 1997-98 tremendous El Nino a duration of better El Nino task existed, and then a shift to extra L. a. Nina task befell. (That is most probably additionally what triggered the prolonged international warming ‘hiatus’ after that El Nino tournament.)

I statistically regressed the L-O values in Fig. 1 towards Three-month operating averages of the Multivariate ENSO Index (MEI), and got rid of that estimate of the ENSO affect from the knowledge. The ensuing ENSO-adjusted time collection in proven in Fig. Three.

Fig. Three. As in Fig. 1, however with the common affect of El Nino and L. a. Nina (ENSO) subtracted out. Observe the proof for a “destroy” in 1998 is way weaker.

Observe the step-up in mid-1998 is way much less obtrusive, and the fifth order polynomial are compatible to the knowledge is smoother with a extra slow transition in L-O over the 41-year satellite tv for pc report.

However that’s no longer the one factor happening all the way through this era that is affecting the L-O values. There have been two primary volcanic eruptions (El Chichon in early 1982, and particularly Pinatubo in mid-1991) that triggered extra cooling over land than ocean, inflicting quickly enhanced detrimental values in L-O. Since those occasions don’t seem to be as simply correlated with an index like MEI is with ENSO, I merely got rid of the knowledge from 1982-83 and 1992-93 in Fig. Three and replotted the ends up in Fig. four.

Fig. four. As in Fig. Three, however with the knowledge influenced through primary volcanoes El Chichon and Pinatubo got rid of.

Now we see that the fifth order polynomial are compatible to the knowledge comes slightly just about the linear development (dashed grey line), which implies that the step-up in 1998 in L-O used to be actual, and comparable most commonly to a metamorphosis in ENSO task earlier than as opposed to after the 1997-98 tremendous El Nino, and with the most important volcanic eruptions in 1982 and 1991 contributing to the reputedly spurious function.

The rest upward development in L-O is solely the land airmasses warming quicker than the sea, as can be anticipated for any warming development, whether or not herbal or human-caused.

There stays what could be a spurious function all the way through 1980-81 in Fig. four, which might possibly be associated with our advert hoc correction for MSU channel Three go with the flow all the way through that point. This, on the other hand, must have little affect at the land and ocean developments as evidenced through the fad line are compatible (dashed grey line) in Fig. four.

Reposted from Dr Roy Spencer’s Weblog

November seventh, 2019 through Roy W. Spencer, Ph. D.

A follower of our UAH international decrease tropospheric temperature (LT) dataset named “JJ” emailed me asking about what could be thought to be a spurious function within the dataset.

The function is most simply noticed should you plot the per thirty days international time collection of Land-minus-Ocean (hereafter “L-O”) temperature anomalies. The end result turns out to turn a step-up of about zero.16 deg. C in Might of 1998.

Fig. 1. Distinction between the UAH decrease tropospheric (LT) land and ocean temperature anomalies between January 1979 and August 2019, appearing an obvious step-up within the distinction happening in Might 1998. The dashed traces display the common values earlier than and after that date, whilst the curve is a fifth order polynomial are compatible to the knowledge.

The yr 1998 is essential for our dataset as a result of this is when the primary (NOAA-15) Complex Microwave Sounding Unit (AMSU) got here on-line, which initiated the transition from the older Microwave Sounding Gadgets (MSU, the closing of which used to be at the NOAA-14 satellite tv for pc).

AMSU didn’t have precisely the similar channel frequency variety because the MSU, so the nominal layers of the ambience sensed had been somewhat other. Most significantly, the AMSU channel five has a weighting serve as that senses relatively extra of the skin and decrease troposphere than MSU channel 2. If one didn’t account for this truth, the AMSU’s better floor sensitivity would produce upper temperatures over land and decrease temperatures over the sea (after a global-average intercalibration between MSU and AMSU used to be carried out). [The reason why is that these channel frequencies are not sensitive to changes in sea surface temperature, because the microwave emissivity decreases as SST increases. The effect is small, but measurable.]

However since those are through-nadir scanners, every view attitude relative to the native vertical measures a somewhat other layer anyway, which permits us to compare the AMSU and MSU measurements. Once we advanced Model 6 of the dataset, we discovered that the 50-60 GHz oxygen absorption concept used to search out the view attitude from AMSU5 that perfect fits MSU2, the ensuing temperature anomalies over land had been nonetheless too heat relative to the oceans. This intended that we needed to carry out an empirical (data-dependent) somewhat than theoretical matching of the AMSU and MSU view angles.

The best way we gauged the fit between MSU and AMSU is how the temperature anomaly patterns transition throughout coastlines: we required that there must be little discernible trade in that development. Sooner than our optimized matching, the land anomalies had been noticeable hotter than the sea anomalies as options crossed coastlines. However after optimization in our Model 6 dataset, right here’s the LT anomaly map for closing month (October 2019), which presentations no proof for land-vs-ocean artifacts.

UAH-global-LT-land-minus-ocean-2

Fig. 2. October 2019 LT temperature anomalies relative to the 1981-2010 common annual cycle. Observe the anomalies have a easy transition between land and ocean, as can be anticipated for deep-layer tropospheric temperatures (however no longer essentially floor temperatures).

However, changes like those are by no means highest. So, the query stays: Is there a spurious trade within the L-O temperature distinction happening in 1998?

Proof that the L-O trade in 1998 is actual

There are a couple of traces of proof that counsel the Might 1998 step-up in L-O temperatures is actual.

First, if the impact used to be because of the advent of AMSU in 1998, it will have befell in August, no longer in Might (Three months earler). Additionally, the impact must were slow since for nearly four years after August 1998 the LT dataset is part MSU (NOAA-14) and part AMSU (NOAA-15), and then it becaume 100% AMSU.

However a extra vital piece of proof is the impact of El Nino and L. a. Nina on L-O. Right through El Nino, the sea airmasses heat greater than the land airmasses (particularly within the tropics), in order that L-O has a tendency to be extra detrimental. Up till the 1997-98 tremendous El Nino a duration of better El Nino task existed, and then a shift to extra L. a. Nina task befell. (That is most probably additionally what triggered the prolonged international warming ‘hiatus’ after that El Nino tournament.)

I statistically regressed the L-O values in Fig. 1 towards Three-month operating averages of the Multivariate ENSO Index (MEI), and got rid of that estimate of the ENSO affect from the knowledge. The ensuing ENSO-adjusted time collection in proven in Fig. Three.

Fig. Three. As in Fig. 1, however with the common affect of El Nino and L. a. Nina (ENSO) subtracted out. Observe the proof for a “destroy” in 1998 is way weaker.

Observe the step-up in mid-1998 is way much less obtrusive, and the fifth order polynomial are compatible to the knowledge is smoother with a extra slow transition in L-O over the 41-year satellite tv for pc report.

However that’s no longer the one factor happening all the way through this era that is affecting the L-O values. There have been two primary volcanic eruptions (El Chichon in early 1982, and particularly Pinatubo in mid-1991) that triggered extra cooling over land than ocean, inflicting quickly enhanced detrimental values in L-O. Since those occasions don’t seem to be as simply correlated with an index like MEI is with ENSO, I merely got rid of the knowledge from 1982-83 and 1992-93 in Fig. Three and replotted the ends up in Fig. four.

Fig. four. As in Fig. Three, however with the knowledge influenced through primary volcanoes El Chichon and Pinatubo got rid of.

Now we see that the fifth order polynomial are compatible to the knowledge comes slightly just about the linear development (dashed grey line), which implies that the step-up in 1998 in L-O used to be actual, and comparable most commonly to a metamorphosis in ENSO task earlier than as opposed to after the 1997-98 tremendous El Nino, and with the most important volcanic eruptions in 1982 and 1991 contributing to the reputedly spurious function.

The rest upward development in L-O is solely the land airmasses warming quicker than the sea, as can be anticipated for any warming development, whether or not herbal or human-caused.

There stays what could be a spurious function all the way through 1980-81 in Fig. four, which might possibly be associated with our advert hoc correction for MSU channel Three go with the flow all the way through that point. This, on the other hand, must have little affect at the land and ocean developments as evidenced through the fad line are compatible (dashed grey line) in Fig. four.

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